Booting the Linux/ppc kernel without Open Firmware
--------------------------------------------------
(c) 2005 Benjamin Herrenschmidt <benh at kernel.crashing.org>,
IBM Corp.
(c) 2005 Becky Bruce <becky.bruce at freescale.com>,
Freescale Semiconductor, FSL SOC and 32-bit additions
(c) 2006 MontaVista Software, Inc.
Flash chip node definition
Table of Contents
=================
I - Introduction
1) Entry point for arch/powerpc
2) Board support
II - The DT block format
1) Header
2) Device tree generalities
3) Device tree "structure" block
4) Device tree "strings" block
III - Required content of the device tree
1) Note about cells and address representation
2) Note about "compatible" properties
3) Note about "name" properties
4) Note about node and property names and character set
5) Required nodes and properties
a) The root node
b) The /cpus node
c) The /cpus/* nodes
d) the /memory node(s)
e) The /chosen node
f) the /soc<SOCname> node
IV - "dtc", the device tree compiler
V - Recommendations for a bootloader
VI - System-on-a-chip devices and nodes
1) Defining child nodes of an SOC
2) Representing devices without a current OF specification
a) PHY nodes
b) Interrupt controllers
c) 4xx/Axon EMAC ethernet nodes
d) Xilinx IP cores
e) USB EHCI controllers
f) MDIO on GPIOs
g) SPI busses
VII - Marvell Discovery mv64[345]6x System Controller chips
1) The /system-controller node
2) Child nodes of /system-controller
a) Marvell Discovery MDIO bus
b) Marvell Discovery ethernet controller
c) Marvell Discovery PHY nodes
d) Marvell Discovery SDMA nodes
e) Marvell Discovery BRG nodes
f) Marvell Discovery CUNIT nodes
g) Marvell Discovery MPSCROUTING nodes
h) Marvell Discovery MPSCINTR nodes
i) Marvell Discovery MPSC nodes
j) Marvell Discovery Watch Dog Timer nodes
k) Marvell Discovery I2C nodes
l) Marvell Discovery PIC (Programmable Interrupt Controller) nodes
m) Marvell Discovery MPP (Multipurpose Pins) multiplexing nodes
n) Marvell Discovery GPP (General Purpose Pins) nodes
o) Marvell Discovery PCI host bridge node
p) Marvell Discovery CPU Error nodes
q) Marvell Discovery SRAM Controller nodes
r) Marvell Discovery PCI Error Handler nodes
s) Marvell Discovery Memory Controller nodes
VIII - Specifying interrupt information for devices
1) interrupts property
2) interrupt-parent property
3) OpenPIC Interrupt Controllers
4) ISA Interrupt Controllers
IX - Specifying GPIO information for devices
1) gpios property
2) gpio-controller nodes
X - Specifying device power management information (sleep property)
Appendix A - Sample SOC node for MPC8540
Revision Information
====================
May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet.
May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or
clarifies the fact that a lot of things are
optional, the kernel only requires a very
small device tree, though it is encouraged
to provide an as complete one as possible.
May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM
- Misc fixes
- Define version 3 and new format version 16
for the DT block (version 16 needs kernel
patches, will be fwd separately).
String block now has a size, and full path
is replaced by unit name for more
compactness.
linux,phandle is made optional, only nodes
that are referenced by other nodes need it.
"name" property is now automatically
deduced from the unit name
June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and
OF_DT_END_NODE in structure definition.
- Change version 16 format to always align
property data to 4 bytes. Since tokens are
already aligned, that means no specific
required alignment between property size
and property data. The old style variable
alignment would make it impossible to do
"simple" insertion of properties using
memmove (thanks Milton for
noticing). Updated kernel patch as well
- Correct a few more alignment constraints
- Add a chapter about the device-tree
compiler and the textural representation of
the tree that can be "compiled" by dtc.
November 21, 2005: Rev 0.5
- Additions/generalizations for 32-bit
- Changed to reflect the new arch/powerpc
structure
- Added chapter VI
ToDo:
- Add some definitions of interrupt tree (simple/complex)
- Add some definitions for PCI host bridges
- Add some common address format examples
- Add definitions for standard properties and "compatible"
names for cells that are not already defined by the existing
OF spec.
- Compare FSL SOC use of PCI to standard and make sure no new
node definition required.
- Add more information about node definitions for SOC devices
that currently have no standard, like the FSL CPM.
I - Introduction
================
During the recent development of the Linux/ppc64 kernel, and more
specifically, the addition of new platform types outside of the old
IBM pSeries/iSeries pair, it was decided to enforce some strict rules
regarding the kernel entry and bootloader <-> kernel interfaces, in
order to avoid the degeneration that had become the ppc32 kernel entry
point and the way a new platform should be added to the kernel. The
legacy iSeries platform breaks those rules as it predates this scheme,
but no new board support will be accepted in the main tree that
doesn't follows them properly. In addition, since the advent of the
arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit
platforms and 32-bit platforms which move into arch/powerpc will be
required to use these rules as well.
The main requirement that will be defined in more detail below is
the presence of a device-tree whose format is defined after Open
Firmware specification. However, in order to make life easier
to embedded board vendors, the kernel doesn't require the device-tree
to represent every device in the system and only requires some nodes
and properties to be present. This will be described in detail in
section III, but, for example, the kernel does not require you to
create a node for every PCI device in the system. It is a requirement
to have a node for PCI host bridges in order to provide interrupt
routing informations and memory/IO ranges, among others. It is also
recommended to define nodes for on chip devices and other busses that
don't specifically fit in an existing OF specification. This creates a
great flexibility in the way the kernel can then probe those and match
drivers to device, without having to hard code all sorts of tables. It
also makes it more flexible for board vendors to do minor hardware
upgrades without significantly impacting the kernel code or cluttering
it with special cases.
1) Entry point for arch/powerpc
-------------------------------
There is one and one single entry point to the kernel, at the start
of the kernel image. That entry point supports two calling
conventions:
a) Boot from Open Firmware. If your firmware is compatible
with Open Firmware (IEEE 1275) or provides an OF compatible
client interface API (support for "interpret" callback of
forth words isn't required), you can enter the kernel with:
r5 : OF callback pointer as defined by IEEE 1275
bindings to powerpc. Only the 32-bit client interface
is currently supported
r3, r4 : address & length of an initrd if any or 0
The MMU is either on or off; the kernel will run the
trampoline located in arch/powerpc/kernel/prom_init.c to
extract the device-tree and other information from open
firmware and build a flattened device-tree as described
in b). prom_init() will then re-enter the kernel using
the second method. This trampoline code runs in the
context of the firmware, which is supposed to handle all
exceptions during that time.
b) Direct entry with a flattened device-tree block. This entry
point is called by a) after the OF trampoline and can also be
called directly by a bootloader that does not support the Open
Firmware client interface. It is also used by "kexec" to
implement "hot" booting of a new kernel from a previous
running one. This method is what I will describe in more
details in this document, as method a) is simply standard Open
Firmware, and thus should be implemented according to the
various standard documents defining it and its binding to the
PowerPC platform. The entry point definition then becomes:
r3 : physical pointer to the device-tree block
(defined in chapter II) in RAM
r4 : physical pointer to the kernel itself. This is
used by the assembly code to properly disable the MMU
in case you are entering the kernel with MMU enabled
and a non-1:1 mapping.
r5 : NULL (as to differentiate with method a)
Note about SMP entry: Either your firmware puts your other
CPUs in some sleep loop or spin loop in ROM where you can get
them out via a soft reset or some other means, in which case
you don't need to care, or you'll have to enter the kernel
with all CPUs. The way to do that with method b) will be
described in a later revision of this document.
2) Board support
----------------
64-bit kernels:
Board supports (platforms) are not exclusive config options. An
arbitrary set of board supports can be built in a single kernel
image. The kernel will "know" what set of functions to use for a
given platform based on the content of the device-tree. Thus, you
should:
a) add your platform support as a _boolean_ option in
arch/powerpc/Kconfig, following the example of PPC_PSERIES,
PPC_PMAC and PPC_MAPLE. The later is probably a good
example of a board support to start from.
b) create your main platform file as
"arch/powerpc/platforms/myplatform/myboard_setup.c" and add it
to the Makefile under the condition of your CONFIG_
option. This file will define a structure of type "ppc_md"
containing the various callbacks that the generic code will
use to get to your platform specific code
c) Add a reference to your "ppc_md" structure in the
"machines" table in arch/powerpc/kernel/setup_64.c if you are
a 64-bit platform.
d) request and get assigned a platform number (see PLATFORM_*
constants in arch/powerpc/include/asm/processor.h
32-bit embedded kernels:
Currently, board support is essentially an exclusive config option.
The kernel is configured for a single platform. Part of the reason
for this is to keep kernels on embedded systems small and efficient;
part of this is due to the fact the code is already that way. In the
future, a kernel may support multiple platforms, but only if the
platforms feature the same core architecture. A single kernel build
cannot support both configurations with Book E and configurations
with classic Powerpc architectures.
32-bit embedded platforms that are moved into arch/powerpc using a
flattened device tree should adopt the merged tree practice of
setting ppc_md up dynamically, even though the kernel is currently
built with support for only a single platform at a time. This allows
unification of the setup code, and will make it easier to go to a
multiple-platform-support model in the future.
NOTE: I believe the above will be true once Ben's done with the merge
of the boot sequences.... someone speak up if this is wrong!
To add a 32-bit embedded platform support, follow the instructions
for 64-bit platforms above, with the exception that the Kconfig
option should be set up such that the kernel builds exclusively for
the platform selected. The processor type for the platform should
enable another config option to select the specific board
supported.
NOTE: If Ben doesn't merge the setup files, may need to change this to
point to setup_32.c
I will describe later the boot process and various callbacks that
your platform should implement.
II - The DT block format
========================
This chapter defines the actual format of the flattened device-tree
passed to the kernel. The actual content of it and kernel requirements
are described later. You can find example of code manipulating that
format in various places, including arch/powerpc/kernel/prom_init.c
which will generate a flattened device-tree from the Open Firmware
representation, or the fs2dt utility which is part of the kexec tools
which will generate one from a filesystem representation. It is
expected that a bootloader like uboot provides a bit more support,
that will be discussed later as well.
Note: The block has to be in main memory. It has to be accessible in
both real mode and virtual mode with no mapping other than main
memory. If you are writing a simple flash bootloader, it should copy
the block to RAM before passing it to the kernel.
1) Header
---------
The kernel is entered with r3 pointing to an area of memory that is
roughly described in arch/powerpc/include/asm/prom.h by the structure
boot_param_header:
struct boot_param_header {
u32 magic; /* magic word OF_DT_HEADER */
u32 totalsize; /* total size of DT block */
u32 off_dt_struct; /* offset to structure */
u32 off_dt_strings; /* offset to strings */
u32 off_mem_rsvmap; /* offset to memory reserve map
*/
u32 version; /* format version */
u32 last_comp_version; /* last compatible version */
/* version 2 fields below */
u32 boot_cpuid_phys; /* Which physical CPU id we're
booting on */
/* version 3 fields below */
u32 size_dt_strings; /* size of the strings block */
/* version 17 fields below */
u32 size_dt_struct; /* size of the DT structure block */
};
Along with the constants:
/* Definitions used by the flattened device tree */
#define OF_DT_HEADER 0xd00dfeed /* 4: version,
4: total size */
#define OF_DT_BEGIN_NODE 0x1 /* Start node: full name
*/
#define OF_DT_END_NODE 0x2 /* End node */
#define OF_DT_PROP 0x3 /* Property: name off,
size, content */
#define OF_DT_END 0x9
All values in this header are in big endian format, the various
fields in this header are defined more precisely below. All
"offset" values are in bytes from the start of the header; that is
from the value of r3.
- magic
This is a magic value that "marks" the beginning of the
device-tree block header. It contains the value 0xd00dfeed and is
defined by the constant OF_DT_HEADER
- totalsize
This is the total size of the DT block including the header. The
"DT" block should enclose all data structures defined in this
chapter (who are pointed to by offsets in this header). That is,
the device-tree structure, strings, and the memory reserve map.
- off_dt_struct
This is an offset from the beginning of the header to the start
of the "structure" part the device tree. (see 2) device tree)
- off_dt_strings
This is an offset from the beginning of the header to the start
of the "strings" part of the device-tree
- off_mem_rsvmap
This is an offset from the beginning of the header to the start
of the reserved memory map. This map is a list of pairs of 64-
bit integers. Each pair is a physical address and a size. The
list is terminated by an entry of size 0. This map provides the
kernel with a list of physical memory areas that are "reserved"
and thus not to be used for memory allocations, especially during
early initialization. The kernel needs to allocate memory during
boot for things like un-flattening the device-tree, allocating an
MMU hash table, etc... Those allocations must be done in such a
way to avoid overriding critical things like, on Open Firmware
capable machines, the RTAS instance, or on some pSeries, the TCE
tables used for the iommu. Typically, the reserve map should
contain _at least_ this DT block itself (header,total_size). If
you are passing an initrd to the kernel, you should reserve it as
well. You do not need to reserve the kernel image itself. The map
should be 64-bit aligned.
- version
This is the version of this structure. Version 1 stops
here. Version 2 adds an additional field boot_cpuid_phys.
Version 3 adds the size of the strings block, allowing the kernel
to reallocate it easily at boot and free up the unused flattened
structure after expansion. Version 16 introduces a new more
"compact" format for the tree itself that is however not backward
compatible. Version 17 adds an additional field, size_dt_struct,
allowing it to be reallocated or moved more easily (this is
particularly useful for bootloaders which need to make
adjustments to a device tree based on probed information). You
should always generate a structure of the highest version defined
at the time of your implementation. Currently that is version 17,
unless you explicitly aim at being backward compatible.
- last_comp_version
Last compatible version. This indicates down to what version of
the DT block you are backward compatible. For example, version 2
is backward compatible with version 1 (that is, a kernel build
for version 1 will be able to boot with a version 2 format). You
should put a 1 in this field if you generate a device tree of
version 1 to 3, or 16 if you generate a tree of version 16 or 17
using the new unit name format.
- boot_cpuid_phys
This field only exist on version 2 headers. It indicate which
physical CPU ID is calling the kernel entry point. This is used,
among others, by kexec. If you are on an SMP system, this value
should match the content of the "reg" property of the CPU node in
the device-tree corresponding to the CPU calling the kernel entry
point (see further chapters for more informations on the required
device-tree contents)
- size_dt_strings
This field only exists on version 3 and later headers. It
gives the size of the "strings" section of the device tree (which
starts at the offset given by off_dt_strings).
- size_dt_struct
This field only exists on version 17 and later headers. It gives
the size of the "structure" section of the device tree (which
starts at the offset given by off_dt_struct).
So the typical layout of a DT block (though the various parts don't
need to be in that order) looks like this (addresses go from top to
bottom):
------------------------------
r3 -> | struct boot_param_header |
------------------------------
| (alignment gap) (*) |
------------------------------
| memory reserve map |
------------------------------
| (alignment gap) |
------------------------------
| |
| device-tree structure |
| |
------------------------------
| (alignment gap) |
------------------------------
| |
| device-tree strings |
| |
-----> ------------------------------
|
|
--- (r3 + totalsize)
(*) The alignment gaps are not necessarily present; their presence
and size are dependent on the various alignment requirements of
the individual data blocks.
2) Device tree generalities
---------------------------
This device-tree itself is separated in two different blocks, a
structure block and a strings block. Both need to be aligned to a 4
byte boundary.
First, let's quickly describe the device-tree concept before detailing
the storage format. This chapter does _not_ describe the detail of the
required types of nodes & properties for the kernel, this is done
later in chapter III.
The device-tree layout is strongly inherited from the definition of
the Open Firmware IEEE 1275 device-tree. It's basically a tree of
nodes, each node having two or more named properties. A property can
have a value or not.
It is a tree, so each node has one and only one parent except for the
root node who has no parent.
A node has 2 names. The actual node name is generally contained in a
property of type "name" in the node property list whose value is a
zero terminated string and is mandatory for version 1 to 3 of the
format definition (as it is in Open Firmware). Version 16 makes it
optional as it can generate it from the unit name defined below.
There is also a "unit name" that is used to differentiate nodes with
the same name at the same level, it is usually made of the node
names, the "@" sign, and a "unit address", which definition is
specific to the bus type the node sits on.
The unit name doesn't exist as a property per-se but is included in
the device-tree structure. It is typically used to represent "path" in
the device-tree. More details about the actual format of these will be
below.
The kernel powerpc generic code does not make any formal use of the
unit address (though some board support code may do) so the only real
requirement here for the unit address is to ensure uniqueness of
the node unit name at a given level of the tree. Nodes with no notion
of address and no possible sibling of the same name (like /memory or
/cpus) may omit the unit address in the context of this specification,
or use the "@0" default unit address. The unit name is used to define
a node "full path", which is the concatenation of all parent node
unit names separated with "/".
The root node doesn't have a defined name, and isn't required to have
a name property either if you are using version 3 or earlier of the
format. It also has no unit address (no @ symbol followed by a unit
address). The root node unit name is thus an empty string. The full
path to the root node is "/".
Every node which actually represents an actual device (that is, a node
which isn't only a virtual "container" for more nodes, like "/cpus"
is) is also required to have a "device_type" property indicating the
type of node .
Finally, every node that can be referenced from a property in another
node is required to have a "linux,phandle" property. Real open
firmware implementations provide a unique "phandle" value for every
node that the "prom_init()" trampoline code turns into
"linux,phandle" properties. However, this is made optional if the
flattened device tree is used directly. An example of a node
referencing another node via "phandle" is when laying out the
interrupt tree which will be described in a further version of this
document.
This "linux, phandle" property is a 32-bit value that uniquely
identifies a node. You are free to use whatever values or system of
values, internal pointers, or whatever to generate these, the only
requirement is that every node for which you provide that property has
a unique value for it.
Here is an example of a simple device-tree. In this example, an "o"
designates a node followed by the node unit name. Properties are
presented with their name followed by their content. "content"
represents an ASCII string (zero terminated) value, while <content>
represents a 32-bit hexadecimal value. The various nodes in this
example will be discussed in a later chapter. At this point, it is
only meant to give you a idea of what a device-tree looks like. I have
purposefully kept the "name" and "linux,phandle" properties which
aren't necessary in order to give you a better idea of what the tree
looks like in practice.
/ o device-tree
|- name = "device-tree"
|- model = "MyBoardName"
|- compatible = "MyBoardFamilyName"
|- #address-cells = <2>
|- #size-cells = <2>
|- linux,phandle = <0>
|
o cpus
| | - name = "cpus"
| | - linux,phandle = <1>
| | - #address-cells = <1>
| | - #size-cells = <0>
| |
| o PowerPC,970@0
| |- name = "PowerPC,970"
| |- device_type = "cpu"
| |- reg = <0>
| |- clock-frequency = <5f5e1000>
| |- 64-bit
| |- linux,phandle = <2>
|
o memory@0
| |- name = "memory"
| |- device_type = "memory"
| |- reg = <00000000 00000000 00000000 20000000>
| |- linux,phandle = <3>
|
o chosen
|- name = "chosen"
|- bootargs = "root=/dev/sda2"
|- linux,phandle = <4>
This tree is almost a minimal tree. It pretty much contains the
minimal set of required nodes and properties to boot a linux kernel;
that is, some basic model informations at the root, the CPUs, and the
physical memory layout. It also includes misc information passed
through /chosen, like in this example, the platform type (mandatory)
and the kernel command line arguments (optional).
The /cpus/PowerPC,970@0/64-bit property is an example of a
property without a value. All other properties have a value. The
significance of the #address-cells and #size-cells properties will be
explained in chapter IV which defines precisely the required nodes and
properties and their content.
3) Device tree "structure" block
The structure of the device tree is a linearized tree structure. The
"OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE"
ends that node definition. Child nodes are simply defined before
"OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32
bit value. The tree has to be "finished" with a OF_DT_END token
Here's the basic structure of a single node:
* token OF_DT_BEGIN_NODE (that is 0x00000001)
* for version 1 to 3, this is the node full path as a zero
terminated string, starting with "/". For version 16 and later,
this is the node unit name only (or an empty string for the
root node)
* [align gap to next 4 bytes boundary]
* for each property:
* token OF_DT_PROP (that is 0x00000003)
* 32-bit value of property value size in bytes (or 0 if no
value)
* 32-bit value of offset in string block of property name
* property value data if any
* [align gap to next 4 bytes boundary]
* [child nodes if any]
* token OF_DT_END_NODE (that is 0x00000002)
So the node content can be summarized as a start token, a full path,
a list of properties, a list of child nodes, and an end token. Every
child node is a full node structure itself as defined above.
NOTE: The above definition requires that all property definitions for
a particular node MUST precede any subnode definitions for that node.
Although the structure would not be ambiguous if properties and
subnodes were intermingled, the kernel parser requires that the
properties come first (up until at least 2.6.22). Any tools
manipulating a flattened tree must take care to preserve this
constraint.
4) Device tree "strings" block
In order to save space, property names, which are generally redundant,
are stored separately in the "strings" block. This block is simply the
whole bunch of zero terminated strings for all property names
concatenated together. The device-tree property definitions in the
structure block will contain offset values from the beginning of the
strings block.
III - Required content of the device tree
=========================================
WARNING: All "linux,*" properties defined in this document apply only
to a flattened device-tree. If your platform uses a real
implementation of Open Firmware or an implementation compatible with
the Open Firmware client interface, those properties will be created
by the trampoline code in the kernel's prom_init() file. For example,
that's where you'll have to add code to detect your board model and
set the platform number. However, when using the flattened device-tree
entry point, there is no prom_init() pass, and thus you have to
provide those properties yourself.
1) Note about cells and address representation
----------------------------------------------
The general rule is documented in the various Open Firmware
documentations. If you choose to describe a bus with the device-tree
and there exist an OF bus binding, then you should follow the
specification. However, the kernel does not require every single
device or bus to be described by the device tree.
In general, the format of an address for a device is defined by the
parent bus type, based on the #address-cells and #size-cells
properties. Note that the parent's parent definitions of #address-cells
and #size-cells are not inherited so every node with children must specify
them. The kernel requires the root node to have those properties defining
addresses format for devices directly mapped on the processor bus.
Those 2 properties define 'cells' for representing an address and a
size. A "cell" is a 32-bit number. For example, if both contain 2
like the example tree given above, then an address and a size are both
composed of 2 cells, and each is a 64-bit number (cells are
concatenated and expected to be in big endian format). Another example
is the way Apple firmware defines them, with 2 cells for an address
and one cell for a size. Most 32-bit implementations should define
#address-cells and #size-cells to 1, which represents a 32-bit value.
Some 32-bit processors allow for physical addresses greater than 32
bits; these processors should define #address-cells as 2.
"reg" properties are always a tuple of the type "address size" where
the number of cells of address and size is specified by the bus
#address-cells and #size-cells. When a bus supports various address
spaces and other flags relative to a given address allocation (like
prefetchable, etc...) those flags are usually added to the top level
bits of the physical address. For example, a PCI physical address is
made of 3 cells, the bottom two containing the actual address itself
while the top cell contains address space indication, flags, and pci
bus & device numbers.
For busses that support dynamic allocation, it's the accepted practice
to then not provide the address in "reg" (keep it 0) though while
providing a flag indicating the address is dynamically allocated, and
then, to provide a separate "assigned-addresses" property that
contains the fully allocated addresses. See the PCI OF bindings for
details.
In general, a simple bus with no address space bits and no dynamic
allocation is preferred if it reflects your hardware, as the existing
kernel address parsing functions will work out of the box. If you
define a bus type with a more complex address format, including things
like address space bits, you'll have to add a bus translator to the
prom_parse.c file of the recent kernels for your bus type.
The "reg" property only defines addresses and sizes (if #size-cells is
non-0) within a given bus. In order to translate addresses upward
(that is into parent bus addresses, and possibly into CPU physical
addresses), all busses must contain a "ranges" property. If the
"ranges" property is missing at a given level, it's assumed that
translation isn't possible, i.e., the registers are not visible on the
parent bus. The format of the "ranges" property for a bus is a list
of:
bus address, parent bus address, size
"bus address" is in the format of the bus this bus node is defining,
that is, for a PCI bridge, it would be a PCI address. Thus, (bus
address, size) defines a range of addresses for child devices. "parent
bus address" is in the format of the parent bus of this bus. For
example, for a PCI host controller, that would be a CPU address. For a
PCI<->ISA bridge, that would be a PCI address. It defines the base
address in the parent bus where the beginning of that range is mapped.
For a new 64-bit powerpc board, I recommend either the 2/2 format or
Apple's 2/1 format which is slightly more compact since sizes usually
fit in a single 32-bit word. New 32-bit powerpc boards should use a
1/1 format, unless the processor supports physical addresses greater
than 32-bits, in which case a 2/1 format is recommended.
Alternatively, the "ranges" property may be empty, indicating that the
registers are visible on the parent bus using an identity mapping
translation. In other words, the parent bus address space is the same
as the child bus address space.
2) Note about "compatible" properties
-------------------------------------
These properties are optional, but recommended in devices and the root
node. The format of a "compatible" property is a list of concatenated
zero terminated strings. They allow a device to express its
compatibility with a family of similar devices, in some cases,
allowing a single driver to match against several devices regardless
of their actual names.
3) Note about "name" properties
-------------------------------
While earlier users of Open Firmware like OldWorld macintoshes tended
to use the actual device name for the "name" property, it's nowadays
considered a good practice to use a name that is closer to the device
class (often equal to device_type). For example, nowadays, ethernet
controllers are named "ethernet", an additional "model" property
defining precisely the chip type/model, and "compatible" property
defining the family in case a single driver can driver more than one
of these chips. However, the kernel doesn't generally put any
restriction on the "name" property; it is simply considered good
practice to follow the standard and its evolutions as closely as
possible.
Note also that the new format version 16 makes the "name" property
optional. If it's absent for a node, then the node's unit name is then
used to reconstruct the name. That is, the part of the unit name
before the "@" sign is used (or the entire unit name if no "@" sign
is present).
4) Note about node and property names and character set
-------------------------------------------------------
While open firmware provides more flexible usage of 8859-1, this
specification enforces more strict rules. Nodes and properties should
be comprised only of ASCII characters 'a' to 'z', '0' to
'9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally
allow uppercase characters 'A' to 'Z' (property names should be
lowercase. The fact that vendors like Apple don't respect this rule is
irrelevant here). Additionally, node and property names should always
begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node
names).
The maximum number of characters for both nodes and property names
is 31. In the case of node names, this is only the leftmost part of
a unit name (the pure "name" property), it doesn't include the unit
address which can extend beyond that limit.
5) Required nodes and properties
--------------------------------
These are all that are currently required. However, it is strongly
recommended that you expose PCI host bridges as documented in the
PCI binding to open firmware, and your interrupt tree as documented
in OF interrupt tree specification.
a) The root node
The root node requires some properties to be present:
- model : this is your board name/model
- #address-cells : address representation for "root" devices
- #size-cells: the size representation for "root" devices
- device_type : This property shouldn't be necessary. However, if
you decide to create a device_type for your root node, make sure it
is _not_ "chrp" unless your platform is a pSeries or PAPR compliant
one for 64-bit, or a CHRP-type machine for 32-bit as this will
matched by the kernel this way.
Additionally, some recommended properties are:
- compatible : the board "family" generally finds its way here,
for example, if you have 2 board models with a similar layout,
that typically get driven by the same platform code in the
kernel, you would use a different "model" property but put a
value in "compatible". The kernel doesn't directly use that
value but it is generally useful.
The root node is also generally where you add additional properties
specific to your board like the serial number if any, that sort of
thing. It is recommended that if you add any "custom" property whose
name may clash with standard defined ones, you prefix them with your
vendor name and a comma.
b) The /cpus node
This node is the parent of all individual CPU nodes. It doesn't
have any specific requirements, though it's generally good practice
to have at least:
#address-cells = <00000001>
#size-cells = <00000000>
This defines that the "address" for a CPU is a single cell, and has
no meaningful size. This is not necessary but the kernel will assume
that format when reading the "reg" properties of a CPU node, see
below
c) The /cpus/* nodes
So under /cpus, you are supposed to create a node for every CPU on
the machine. There is no specific restriction on the name of the
CPU, though It's common practice to call it PowerPC,<name>. For
example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX.
Required properties:
- device_type : has to be "cpu"
- reg : This is the physical CPU number, it's a single 32-bit cell
and is also used as-is as the unit number for constructing the
unit name in the full path. For example, with 2 CPUs, you would
have the full path:
/cpus/PowerPC,970FX@0
/cpus/PowerPC,970FX@1
(unit addresses do not require leading zeroes)
- d-cache-block-size : one cell, L1 data cache block size in bytes (*)
- i-cache-block-size : one cell, L1 instruction cache block size in
bytes
- d-cache-size : one cell, size of L1 data cache in bytes
- i-cache-size : one cell, size of L1 instruction cache in bytes
(*) The cache "block" size is the size on which the cache management
instructions operate. Historically, this document used the cache
"line" size here which is incorrect. The kernel will prefer the cache
block size and will fallback to cache line size for backward
compatibility.
Recommended properties:
- timebase-frequency : a cell indicating the frequency of the
timebase in Hz. This is not directly used by the generic code,
but you are welcome to copy/paste the pSeries code for setting
the kernel timebase/decrementer calibration based on this
value.
- clock-frequency : a cell indicating the CPU core clock frequency
in Hz. A new property will be defined for 64-bit values, but if
your frequency is < 4Ghz, one cell is enough. Here as well as
for the above, the common code doesn't use that property, but
you are welcome to re-use the pSeries or Maple one. A future
kernel version might provide a common function for this.
- d-cache-line-size : one cell, L1 data cache line size in bytes
if different from the block size
- i-cache-line-size : one cell, L1 instruction cache line size in
bytes if different from the block size
You are welcome to add any property you find relevant to your board,
like some information about the mechanism used to soft-reset the
CPUs. For example, Apple puts the GPIO number for CPU soft reset
lines in there as a "soft-reset" property since they start secondary
CPUs by soft-resetting them.
d) the /memory node(s)
To define the physical memory layout of your board, you should
create one or more memory node(s). You can either create a single
node with all memory ranges in its reg property, or you can create
several nodes, as you wish. The unit address (@ part) used for the
full path is the address of the first range of memory defined by a
given node. If you use a single memory node, this will typically be
@0.
Required properties:
- device_type : has to be "memory"
- reg : This property contains all the physical memory ranges of
your board. It's a list of addresses/sizes concatenated
together, with the number of cells of each defined by the
#address-cells and #size-cells of the root node. For example,
with both of these properties being 2 like in the example given
earlier, a 970 based machine with 6Gb of RAM could typically
have a "reg" property here that looks like:
00000000 00000000 00000000 80000000
00000001 00000000 00000001 00000000
That is a range starting at 0 of 0x80000000 bytes and a range
starting at 0x100000000 and of 0x100000000 bytes. You can see
that there is no memory covering the IO hole between 2Gb and
4Gb. Some vendors prefer splitting those ranges into smaller
segments, but the kernel doesn't care.
e) The /chosen node
This node is a bit "special". Normally, that's where open firmware
puts some variable environment information, like the arguments, or
the default input/output devices.
This specification makes a few of these mandatory, but also defines
some linux-specific properties that would be normally constructed by
the prom_init() trampoline when booting with an OF client interface,
but that you have to provide yourself when using the flattened format.
Recommended properties:
- bootargs : This zero-terminated string is passed as the kernel
command line
- linux,stdout-path : This is the full path to your standard
console device if any. Typically, if you have serial devices on
your board, you may want to put the full path to the one set as
the default console in the firmware here, for the kernel to pick
it up as its own default console. If you look at the function
set_preferred_console() in arch/ppc64/kernel/setup.c, you'll see
that the kernel tries to find out the default console and has
knowledge of various types like 8250 serial ports. You may want
to extend this function to add your own.
Note that u-boot creates and fills in the chosen node for platforms
that use it.
(Note: a practice that is now obsolete was to include a property
under /chosen called interrupt-controller which had a phandle value
that pointed to the main interrupt controller)
f) the /soc<SOCname> node
This node is used to represent a system-on-a-chip (SOC) and must be
present if the processor is a SOC. The top-level soc node contains
information that is global to all devices on the SOC. The node name
should contain a unit address for the SOC, which is the base address
of the memory-mapped register set for the SOC. The name of an soc
node should start with "soc", and the remainder of the name should
represent the part number for the soc. For example, the MPC8540's
soc node would be called "soc8540".
Required properties:
- device_type : Should be "soc"
- ranges : Should be defined as specified in 1) to describe the
translation of SOC addresses for memory mapped SOC registers.
- bus-frequency: Contains the bus frequency for the SOC node.
Typically, the value of this field is filled in by the boot
loader.
Recommended properties:
- reg : This property defines the address and size of the
memory-mapped registers that are used for the SOC node itself.
It does not include the child device registers - these will be
defined inside each child node. The address specified in the
"reg" property should match the unit address of the SOC node.
- #address-cells : Address representation for "soc" devices. The
format of this field may vary depending on whether or not the
device registers are memory mapped. For memory mapped
registers, this field represents the number of cells needed to
represent the address of the registers. For SOCs that do not
use MMIO, a special address format should be defined that
contains enough cells to represent the required information.
See 1) above for more details on defining #address-cells.
- #size-cells : Size representation for "soc" devices
- #interrupt-cells : Defines the width of cells used to represent
interrupts. Typically this value is <2>, which includes a
32-bit number that represents the interrupt number, and a
32-bit number that represents the interrupt sense and level.
This field is only needed if the SOC contains an interrupt
controller.
The SOC node may contain child nodes for each SOC device that the
platform uses. Nodes should not be created for devices which exist
on the SOC but are not used by a particular platform. See chapter VI
for more information on how to specify devices that are part of a SOC.
Example SOC node for the MPC8540:
soc8540@e0000000 {
#address-cells = <1>;
#size-cells = <1>;
#interrupt-cells = <2>;
device_type = "soc";
ranges = <00000000 e0000000 00100000>
reg = <e0000000 00003000>;
bus-frequency = <0>;
}
IV - "dtc", the device tree compiler
====================================
dtc source code can be found at
<http://ozlabs.org/~dgibson/dtc/dtc.tar.gz>
WARNING: This version is still in early development stage; the
resulting device-tree "blobs" have not yet been validated with the
kernel. The current generated bloc lacks a useful reserve map (it will
be fixed to generate an empty one, it's up to the bootloader to fill
it up) among others. The error handling needs work, bugs are lurking,
etc...
dtc basically takes a device-tree in a given format and outputs a
device-tree in another format. The currently supported formats are:
Input formats:
-------------
- "dtb": "blob" format, that is a flattened device-tree block
with
header all in a binary blob.
- "dts": "source" format. This is a text file containing a
"source" for a device-tree. The format is defined later in this
chapter.
- "fs" format. This is a representation equivalent to the
output of /proc/device-tree, that is nodes are directories and
properties are files
Output formats:
---------------
- "dtb": "blob" format
- "dts": "source" format
- "asm": assembly language file. This is a file that can be
sourced by gas to generate a device-tree "blob". That file can
then simply be added to your Makefile. Additionally, the
assembly file exports some symbols that can be used.
The syntax of the dtc tool is
dtc [-I <input-format>] [-O <output-format>]
[-o output-filename] [-V output_version] input_filename
The "output_version" defines what version of the "blob" format will be
generated. Supported versions are 1,2,3 and 16. The default is
currently version 3 but that may change in the future to version 16.
Additionally, dtc performs various sanity checks on the tree, like the
uniqueness of linux, phandle properties, validity of strings, etc...
The format of the .dts "source" file is "C" like, supports C and C++
style comments.
/ {
}
The above is the "device-tree" definition. It's the only statement
supported currently at the toplevel.
/ {
property1 = "string_value"; /* define a property containing a 0
* terminated string
*/
property2 = <1234abcd>; /* define a property containing a
* numerical 32-bit value (hexadecimal)
*/
property3 = <12345678 12345678 deadbeef>;
/* define a property containing 3
* numerical 32-bit values (cells) in
* hexadecimal
*/
property4 = [0a 0b 0c 0d de ea ad be ef];
/* define a property whose content is
* an arbitrary array of bytes
*/
childnode@addresss { /* define a child node named "childnode"
* whose unit name is "childnode at
* address"
*/
childprop = "hello\n"; /* define a property "childprop" of
* childnode (in this case, a string)
*/
};
};
Nodes can contain other nodes etc... thus defining the hierarchical
structure of the tree.
Strings support common escape sequences from C: "\n", "\t", "\r",
"\(octal value)", "\x(hex value)".
It is also suggested that you pipe your source file through cpp (gcc
preprocessor) so you can use #include's, #define for constants, etc...
Finally, various options are planned but not yet implemented, like
automatic generation of phandles, labels (exported to the asm file so
you can point to a property content and change it easily from whatever
you link the device-tree with), label or path instead of numeric value
in some cells to "point" to a node (replaced by a phandle at compile
time), export of reserve map address to the asm file, ability to
specify reserve map content at compile time, etc...
We may provide a .h include file with common definitions of that
proves useful for some properties (like building PCI properties or
interrupt maps) though it may be better to add a notion of struct
definitions to the compiler...
V - Recommendations for a bootloader
====================================
Here are some various ideas/recommendations that have been proposed
while all this has been defined and implemented.
- The bootloader may want to be able to use the device-tree itself
and may want to manipulate it (to add/edit some properties,
like physical memory size or kernel arguments). At this point, 2
choices can be made. Either the bootloader works directly on the
flattened format, or the bootloader has its own internal tree
representation with pointers (similar to the kernel one) and
re-flattens the tree when booting the kernel. The former is a bit
more difficult to edit/modify, the later requires probably a bit
more code to handle the tree structure. Note that the structure
format has been designed so it's relatively easy to "insert"
properties or nodes or delete them by just memmoving things
around. It contains no internal offsets or pointers for this
purpose.
- An example of code for iterating nodes & retrieving properties
directly from the flattened tree format can be found in the kernel
file arch/ppc64/kernel/prom.c, look at scan_flat_dt() function,
its usage in early_init_devtree(), and the corresponding various
early_init_dt_scan_*() callbacks. That code can be re-used in a
GPL bootloader, and as the author of that code, I would be happy
to discuss possible free licensing to any vendor who wishes to
integrate all or part of this code into a non-GPL bootloader.
VI - System-on-a-chip devices and nodes
=======================================
Many companies are now starting to develop system-on-a-chip
processors, where the processor core (CPU) and many peripheral devices
exist on a single piece of silicon. For these SOCs, an SOC node
should be used that defines child nodes for the devices that make
up the SOC. While platforms are not required to use this model in
order to boot the kernel, it is highly encouraged that all SOC
implementations define as complete a flat-device-tree as possible to
describe the devices on the SOC. This will allow for the
genericization of much of the kernel code.
1) Defining child nodes of an SOC
---------------------------------
Each device that is part of an SOC may have its own node entry inside
the SOC node. For each device that is included in the SOC, the unit
address property represents the address offset for this device's
memory-mapped registers in the parent's address space. The parent's
address space is defined by the "ranges" property in the top-level soc
node. The "reg" property for each node that exists directly under the
SOC node should contain the address mapping from the child address space
to the parent SOC address space and the size of the device's
memory-mapped register file.
For many devices that may exist inside an SOC, there are predefined
specifications for the format of the device tree node. All SOC child
nodes should follow these specifications, except where noted in this
document.
See appendix A for an example partial SOC node definition for the
MPC8540.
2) Representing devices without a current OF specification
----------------------------------------------------------
Currently, there are many devices on SOCs that do not have a standard
representation pre-defined as part of the open firmware
specifications, mainly because the boards that contain these SOCs are
not currently booted using open firmware. This section contains
descriptions for the SOC devices for which new nodes have been
defined; this list will expand as more and more SOC-containing
platforms are moved over to use the flattened-device-tree model.
a) PHY nodes
Required properties:
- device_type : Should be "ethernet-phy"
- interrupts : <a b> where a is the interrupt number and b is a
field that represents an encoding of the sense and level
information for the interrupt. This should be encoded based on
the information in section 2) depending on the type of interrupt
controller you have.
- interrupt-parent : the phandle for the interrupt controller that
services interrupts for this device.
- reg : The ID number for the phy, usually a small integer
- linux,phandle : phandle for this node; likely referenced by an
ethernet controller node.
Example:
ethernet-phy@0 {
linux,phandle = <2452000>
interrupt-parent = <40000>;
interrupts = <35 1>;
reg = <0>;
device_type = "ethernet-phy";
};
b) Interrupt controllers
Some SOC devices contain interrupt controllers that are different
from the standard Open PIC specification. The SOC device nodes for
these types of controllers should be specified just like a standard
OpenPIC controller. Sense and level information should be encoded
as specified in section 2) of this chapter for each device that
specifies an interrupt.
Example :
pic@40000 {
linux,phandle = <40000>;
interrupt-controller;
#address-cells = <0>;
reg = <40000 40000>;
compatible = "chrp,open-pic";
device_type = "open-pic";
};
c) 4xx/Axon EMAC ethernet nodes
The EMAC ethernet controller in IBM and AMCC 4xx chips, and also
the Axon bridge. To operate this needs to interact with a ths
special McMAL DMA controller, and sometimes an RGMII or ZMII
interface. In addition to the nodes and properties described
below, the node for the OPB bus on which the EMAC sits must have a
correct clock-frequency property.
i) The EMAC node itself
Required properties:
- device_type : "network"
- compatible : compatible list, contains 2 entries, first is
"ibm,emac-CHIP" where CHIP is the host ASIC (440gx,
405gp, Axon) and second is either "ibm,emac" or
"ibm,emac4". For Axon, thus, we have: "ibm,emac-axon",
"ibm,emac4"
- interrupts : <interrupt mapping for EMAC IRQ and WOL IRQ>
- interrupt-parent : optional, if needed for interrupt mapping
- reg : <registers mapping>
- local-mac-address : 6 bytes, MAC address
- mal-device : phandle of the associated McMAL node
- mal-tx-channel : 1 cell, index of the tx channel on McMAL associated
with this EMAC
- mal-rx-channel : 1 cell, index of the rx channel on McMAL associated
with this EMAC
- cell-index : 1 cell, hardware index of the EMAC cell on a given
ASIC (typically 0x0 and 0x1 for EMAC0 and EMAC1 on
each Axon chip)
- max-frame-size : 1 cell, maximum frame size supported in bytes
- rx-fifo-size : 1 cell, Rx fifo size in bytes for 10 and 100 Mb/sec
operations.
For Axon, 2048
- tx-fifo-size : 1 cell, Tx fifo size in bytes for 10 and 100 Mb/sec
operations.
For Axon, 2048.
- fifo-entry-size : 1 cell, size of a fifo entry (used to calculate
thresholds).
For Axon, 0x00000010
- mal-burst-size : 1 cell, MAL burst size (used to calculate thresholds)
in bytes.
For Axon, 0x00000100 (I think ...)
- phy-mode : string, mode of operations of the PHY interface.
Supported values are: "mii", "rmii", "smii", "rgmii",
"tbi", "gmii", rtbi", "sgmii".
For Axon on CAB, it is "rgmii"
- mdio-device : 1 cell, required iff using shared MDIO registers
(440EP). phandle of the EMAC to use to drive the
MDIO lines for the PHY used by this EMAC.
- zmii-device : 1 cell, required iff connected to a ZMII. phandle of
the ZMII device node
- zmii-channel : 1 cell, required iff connected to a ZMII. Which ZMII
channel or 0xffffffff if ZMII is only used for MDIO.
- rgmii-device : 1 cell, required iff connected to an RGMII. phandle
of the RGMII device node.
For Axon: phandle of plb5/plb4/opb/rgmii
- rgmii-channel : 1 cell, required iff connected to an RGMII. Which
RGMII channel is used by this EMAC.
Fox Axon: present, whatever value is appropriate for each
EMAC, that is the content of the current (bogus) "phy-port"
property.
Optional properties:
- phy-address : 1 cell, optional, MDIO address of the PHY. If absent,
a search is performed.
- phy-map : 1 cell, optional, bitmap of addresses to probe the PHY
for, used if phy-address is absent. bit 0x00000001 is
MDIO address 0.
For Axon it can be absent, though my current driver
doesn't handle phy-address yet so for now, keep
0x00ffffff in it.
- rx-fifo-size-gige : 1 cell, Rx fifo size in bytes for 1000 Mb/sec
operations (if absent the value is the same as
rx-fifo-size). For Axon, either absent or 2048.
- tx-fifo-size-gige : 1 cell, Tx fifo size in bytes for 1000 Mb/sec
operations (if absent the value is the same as
tx-fifo-size). For Axon, either absent or 2048.
- tah-device : 1 cell, optional. If connected to a TAH engine for
offload, phandle of the TAH device node.
- tah-channel : 1 cell, optional. If appropriate, channel used on the
TAH engine.
Example:
EMAC0: ethernet@40000800 {
device_type = "network";
compatible = "ibm,emac-440gp", "ibm,emac";
interrupt-parent = <&UIC1>;
interrupts = <1c 4 1d 4>;
reg = <40000800 70>;
local-mac-address = [00 04 AC E3 1B 1E];
mal-device = <&MAL0>;
mal-tx-channel = <0 1>;
mal-rx-channel = <0>;
cell-index = <0>;
max-frame-size = <5dc>;
rx-fifo-size = <1000>;
tx-fifo-size = <800>;
phy-mode = "rmii";
phy-map = <00000001>;
zmii-device = <&ZMII0>;
zmii-channel = <0>;
};
ii) McMAL node
Required properties:
- device_type : "dma-controller"
- compatible : compatible list, containing 2 entries, first is
"ibm,mcmal-CHIP" where CHIP is the host ASIC (like
emac) and the second is either "ibm,mcmal" or
"ibm,mcmal2".
For Axon, "ibm,mcmal-axon","ibm,mcmal2"
- interrupts : <interrupt mapping for the MAL interrupts sources:
5 sources: tx_eob, rx_eob, serr, txde, rxde>.
For Axon: This is _different_ from the current
firmware. We use the "delayed" interrupts for txeob
and rxeob. Thus we end up with mapping those 5 MPIC
interrupts, all level positive sensitive: 10, 11, 32,
33, 34 (in decimal)
- dcr-reg : < DCR registers range >
- dcr-parent : if needed for dcr-reg
- num-tx-chans : 1 cell, number of Tx channels
- num-rx-chans : 1 cell, number of Rx channels
iii) ZMII node
Required properties:
- compatible : compatible list, containing 2 entries, first is
"ibm,zmii-CHIP" where CHIP is the host ASIC (like
EMAC) and the second is "ibm,zmii".
For Axon, there is no ZMII node.
- reg : <registers mapping>
iv) RGMII node
Required properties:
- compatible : compatible list, containing 2 entries, first is
"ibm,rgmii-CHIP" where CHIP is the host ASIC (like
EMAC) and the second is "ibm,rgmii".
For Axon, "ibm,rgmii-axon","ibm,rgmii"
- reg : <registers mapping>
- revision : as provided by the RGMII new version register if
available.
For Axon: 0x0000012a
d) Xilinx IP cores
The Xilinx EDK toolchain ships with a set of IP cores (devices) for use
in Xilinx Spartan and Virtex FPGAs. The devices cover the whole range
of standard device types (network, serial, etc.) and miscellaneous
devices (gpio, LCD, spi, etc). Also, since these devices are
implemented within the fpga fabric every instance of the device can be
synthesised with different options that change the behaviour.
Each IP-core has a set of parameters which the FPGA designer can use to
control how the core is synthesized. Historically, the EDK tool would
extract the device parameters relevant to device drivers and copy them
into an 'xparameters.h' in the form of #define symbols. This tells the
device drivers how the IP cores are configured, but it requres the kernel
to be recompiled every time the FPGA bitstream is resynthesized.
The new approach is to export the parameters into the device tree and
generate a new device tree each time the FPGA bitstream changes. The
parameters which used to be exported as #defines will now become
properties of the device node. In general, device nodes for IP-cores
will take the following form:
(name): (generic-name)@(base-address) {
compatible = "xlnx,(ip-core-name)-(HW_VER)"
[, (list of compatible devices), ...];
reg = <(baseaddr) (size)>;
interrupt-parent = <&interrupt-controller-phandle>;
interrupts = < ... >;
xlnx,(parameter1) = "(string-value)";
xlnx,(parameter2) = <(int-value)>;
};
(generic-name): an open firmware-style name that describes the
generic class of device. Preferably, this is one word, such
as 'serial' or 'ethernet'.
(ip-core-name): the name of the ip block (given after the BEGIN
directive in system.mhs). Should be in lowercase
and all underscores '_' converted to dashes '-'.
(name): is derived from the "PARAMETER INSTANCE" value.
(parameter#): C_* parameters from system.mhs. The C_ prefix is
dropped from the parameter name, the name is converted
to lowercase and all underscore '_' characters are
converted to dashes '-'.
(baseaddr): the baseaddr parameter value (often named C_BASEADDR).
(HW_VER): from the HW_VER parameter.
(size): the address range size (often C_HIGHADDR - C_BASEADDR + 1).
Typically, the compatible list will include the exact IP core version
followed by an older IP core version which implements the same
interface or any other device with the same interface.
'reg', 'interrupt-parent' and 'interrupts' are all optional properties.
For example, the following block from system.mhs:
BEGIN opb_uartlite
PARAMETER INSTANCE = opb_uartlite_0
PARAMETER HW_VER = 1.00.b
PARAMETER C_BAUDRATE = 115200
PARAMETER C_DATA_BITS = 8
PARAMETER C_ODD_PARITY = 0
PARAMETER C_USE_PARITY = 0
PARAMETER C_CLK_FREQ = 50000000
PARAMETER C_BASEADDR = 0xEC100000
PARAMETER C_HIGHADDR = 0xEC10FFFF
BUS_INTERFACE SOPB = opb_7
PORT OPB_Clk = CLK_50MHz
PORT Interrupt = opb_uartlite_0_Interrupt
PORT RX = opb_uartlite_0_RX
PORT TX = opb_uartlite_0_TX
PORT OPB_Rst = sys_bus_reset_0
END
becomes the following device tree node:
opb_uartlite_0: serial@ec100000 {
device_type = "serial";
compatible = "xlnx,opb-uartlite-1.00.b";
reg = <ec100000 10000>;
interrupt-parent = <&opb_intc_0>;
interrupts = <1 0>; // got this from the opb_intc parameters
current-speed = <d#115200>; // standard serial device prop
clock-frequency = <d#50000000>; // standard serial device prop
xlnx,data-bits = <8>;
xlnx,odd-parity = <0>;
xlnx,use-parity = <0>;
};
Some IP cores actually implement 2 or more logical devices. In
this case, the device should still describe the whole IP core with
a single node and add a child node for each logical device. The
ranges property can be used to translate from parent IP-core to the
registers of each device. In addition, the parent node should be
compatible with the bus type 'xlnx,compound', and should contain
#address-cells and #size-cells, as with any other bus. (Note: this
makes the assumption that both logical devices have the same bus
binding. If this is not true, then separate nodes should be used
for each logical device). The 'cell-index' property can be used to
enumerate logical devices within an IP core. For example, the
following is the system.mhs entry for the dual ps2 controller found
on the ml403 reference design.
BEGIN opb_ps2_dual_ref
PARAMETER INSTANCE = opb_ps2_dual_ref_0
PARAMETER HW_VER = 1.00.a
PARAMETER C_BASEADDR = 0xA9000000
PARAMETER C_HIGHADDR = 0xA9001FFF
BUS_INTERFACE SOPB = opb_v20_0
PORT Sys_Intr1 = ps2_1_intr
PORT Sys_Intr2 = ps2_2_intr
PORT Clkin1 = ps2_clk_rx_1
PORT Clkin2 = ps2_clk_rx_2
PORT Clkpd1 = ps2_clk_tx_1
PORT Clkpd2 = ps2_clk_tx_2
PORT Rx1 = ps2_d_rx_1
PORT Rx2 = ps2_d_rx_2
PORT Txpd1 = ps2_d_tx_1
PORT Txpd2 = ps2_d_tx_2
END
It would result in the following device tree nodes:
opb_ps2_dual_ref_0: opb-ps2-dual-ref@a9000000 {
#address-cells = <1>;
#size-cells = <1>;
compatible = "xlnx,compound";
ranges = <0 a9000000 2000>;
// If this device had extra parameters, then they would
// go here.
ps2@0 {
compatible = "xlnx,opb-ps2-dual-ref-1.00.a";
reg = <0 40>;
interrupt-parent = <&opb_intc_0>;
interrupts = <3 0>;
cell-index = <0>;
};
ps2@1000 {
compatible = "xlnx,opb-ps2-dual-ref-1.00.a";
reg = <1000 40>;
interrupt-parent = <&opb_intc_0>;
interrupts = <3 0>;
cell-index = <0>;
};
};
Also, the system.mhs file defines bus attachments from the processor
to the devices. The device tree structure should reflect the bus
attachments. Again an example; this system.mhs fragment:
BEGIN ppc405_virtex4
PARAMETER INSTANCE = ppc405_0
PARAMETER HW_VER = 1.01.a
BUS_INTERFACE DPLB = plb_v34_0
BUS_INTERFACE IPLB = plb_v34_0
END
BEGIN opb_intc
PARAMETER INSTANCE = opb_intc_0
PARAMETER HW_VER = 1.00.c
PARAMETER C_BASEADDR = 0xD1000FC0
PARAMETER C_HIGHADDR = 0xD1000FDF
BUS_INTERFACE SOPB = opb_v20_0
END
BEGIN opb_uart16550
PARAMETER INSTANCE = opb_uart16550_0
PARAMETER HW_VER = 1.00.d
PARAMETER C_BASEADDR = 0xa0000000
PARAMETER C_HIGHADDR = 0xa0001FFF
BUS_INTERFACE SOPB = opb_v20_0
END
BEGIN plb_v34
PARAMETER INSTANCE = plb_v34_0
PARAMETER HW_VER = 1.02.a
END
BEGIN plb_bram_if_cntlr
PARAMETER INSTANCE = plb_bram_if_cntlr_0
PARAMETER HW_VER = 1.00.b
PARAMETER C_BASEADDR = 0xFFFF0000
PARAMETER C_HIGHADDR = 0xFFFFFFFF
BUS_INTERFACE SPLB = plb_v34_0
END
BEGIN plb2opb_bridge
PARAMETER INSTANCE = plb2opb_bridge_0
PARAMETER HW_VER = 1.01.a
PARAMETER C_RNG0_BASEADDR = 0x20000000
PARAMETER C_RNG0_HIGHADDR = 0x3FFFFFFF
PARAMETER C_RNG1_BASEADDR = 0x60000000
PARAMETER C_RNG1_HIGHADDR = 0x7FFFFFFF
PARAMETER C_RNG2_BASEADDR = 0x80000000
PARAMETER C_RNG2_HIGHADDR = 0xBFFFFFFF
PARAMETER C_RNG3_BASEADDR = 0xC0000000
PARAMETER C_RNG3_HIGHADDR = 0xDFFFFFFF
BUS_INTERFACE SPLB = plb_v34_0
BUS_INTERFACE MOPB = opb_v20_0
END
Gives this device tree (some properties removed for clarity):
plb@0 {
#address-cells = <1>;
#size-cells = <1>;
compatible = "xlnx,plb-v34-1.02.a";
device_type = "ibm,plb";
ranges; // 1:1 translation
plb_bram_if_cntrl_0: bram@ffff0000 {
reg = <ffff0000 10000>;
}
opb@20000000 {
#address-cells = <1>;
#size-cells = <1>;
ranges = <20000000 20000000 20000000
60000000 60000000 20000000
80000000 80000000 40000000
c0000000 c0000000 20000000>;
opb_uart16550_0: serial@a0000000 {
reg = <a00000000 2000>;
};
opb_intc_0: interrupt-controller@d1000fc0 {
reg = <d1000fc0 20>;
};
};
};
That covers the general approach to binding xilinx IP cores into the
device tree. The following are bindings for specific devices:
i) Xilinx ML300 Framebuffer
Simple framebuffer device from the ML300 reference design (also on the
ML403 reference design as well as others).
Optional properties:
- resolution = <xres yres> : pixel resolution of framebuffer. Some
implementations use a different resolution.
Default is <d#640 d#480>
- virt-resolution = <xvirt yvirt> : Size of framebuffer in memory.
Default is <d#1024 d#480>.
- rotate-display (empty) : rotate display 180 degrees.
ii) Xilinx SystemACE
The Xilinx SystemACE device is used to program FPGAs from an FPGA
bitstream stored on a CF card. It can also be used as a generic CF
interface device.
Optional properties:
- 8-bit (empty) : Set this property for SystemACE in 8 bit mode
iii) Xilinx EMAC and Xilinx TEMAC
Xilinx Ethernet devices. In addition to general xilinx properties
listed above, nodes for these devices should include a phy-handle
property, and may include other common network device properties
like local-mac-address.
iv) Xilinx Uartlite
Xilinx uartlite devices are simple fixed speed serial ports.
Required properties:
- current-speed : Baud rate of uartlite
v) Xilinx hwicap
Xilinx hwicap devices provide access to the configuration logic
of the FPGA through the Internal Configuration Access Port
(ICAP). The ICAP enables partial reconfiguration of the FPGA,
readback of the configuration information, and some control over
'warm boots' of the FPGA fabric.
Required properties:
- xlnx,family : The family of the FPGA, necessary since the
capabilities of the underlying ICAP hardware
differ between different families. May be
'virtex2p', 'virtex4', or 'virtex5'.
vi) Xilinx Uart 16550
Xilinx UART 16550 devices are very similar to the NS16550 but with
different register spacing and an offset from the base address.
Required properties:
- clock-frequency : Frequency of the clock input
- reg-offset : A value of 3 is required
- reg-shift : A value of 2 is required
e) USB EHCI controllers
Required properties:
- compatible : should be "usb-ehci".
- reg : should contain at least address and length of the standard EHCI
register set for the device. Optional platform-dependent registers
(debug-port or other) can be also specified here, but only after
definition of standard EHCI registers.
- interrupts : one EHCI interrupt should be described here.
If device registers are implemented in big endian mode, the device
node should have "big-endian-regs" property.
If controller implementation operates with big endian descriptors,
"big-endian-desc" property should be specified.
If both big endian registers and descriptors are used by the controller
implementation, "big-endian" property can be specified instead of having
both "big-endian-regs" and "big-endian-desc".
Example (Sequoia 440EPx):
ehci@e0000300 {
compatible = "ibm,usb-ehci-440epx", "usb-ehci";
interrupt-parent = <&UIC0>;
interrupts = <1a 4>;
reg = <0 e0000300 90 0 e0000390 70>;
big-endian;
};
f) MDIO on GPIOs
Currently defined compatibles:
- virtual,gpio-mdio
MDC and MDIO lines connected to GPIO controllers are listed in the
gpios property as described in section VIII.1 in the following order:
MDC, MDIO.
Example:
mdio {
compatible = "virtual,mdio-gpio";
#address-cells = <1>;
#size-cells = <0>;
gpios = <&qe_pio_a 11
&qe_pio_c 6>;
};
g) SPI (Serial Peripheral Interface) busses
SPI busses can be described with a node for the SPI master device
and a set of child nodes for each SPI slave on the bus. For this
discussion, it is assumed that the system's SPI controller is in
SPI master mode. This binding does not describe SPI controllers
in slave mode.
The SPI master node requires the following properties:
- #address-cells - number of cells required to define a chip select
address on the SPI bus.
- #size-cells - should be zero.
- compatible - name of SPI bus controller following generic names
recommended practice.
No other properties are required in the SPI bus node. It is assumed
that a driver for an SPI bus device will understand that it is an SPI bus.
However, the binding does not attempt to define the specific method for
assigning chip select numbers. Since SPI chip select configuration is
flexible and non-standardized, it is left out of this binding with the
assumption that board specific platform code will be used to manage
chip selects. Individual drivers can define additional properties to
support describing the chip select layout.
SPI slave nodes must be children of the SPI master node and can
contain the following properties.
- reg - (required) chip select address of device.
- compatible - (required) name of SPI device following generic names
recommended practice
- spi-max-frequency - (required) Maximum SPI clocking speed of device in Hz
- spi-cpol - (optional) Empty property indicating device requires
inverse clock polarity (CPOL) mode
- spi-cpha - (optional) Empty property indicating device requires
shifted clock phase (CPHA) mode
- spi-cs-high - (optional) Empty property indicating device requires
chip select active high
SPI example for an MPC5200 SPI bus:
spi@f00 {
#address-cells = <1>;
#size-cells = <0>;
compatible = "fsl,mpc5200b-spi","fsl,mpc5200-spi";
reg = <0xf00 0x20>;
interrupts = <2 13 0 2 14 0>;
interrupt-parent = <&mpc5200_pic>;
ethernet-switch@0 {
compatible = "micrel,ks8995m";
spi-max-frequency = <1000000>;
reg = <0>;
};
codec@1 {
compatible = "ti,tlv320aic26";
spi-max-frequency = <100000>;
reg = <1>;
};
};
VII - Marvell Discovery mv64[345]6x System Controller chips
===========================================================
The Marvell mv64[345]60 series of system controller chips contain
many of the peripherals needed to implement a complete computer
system. In this section, we define device tree nodes to describe
the system controller chip itself and each of the peripherals
which it contains. Compatible string values for each node are
prefixed with the string "marvell,", for Marvell Technology Group Ltd.
1) The /system-controller node
This node is used to represent the system-controller and must be
present when the system uses a system controller chip. The top-level
system-controller node contains information that is global to all
devices within the system controller chip. The node name begins
with "system-controller" followed by the unit address, which is
the base address of the memory-mapped register set for the system
controller chip.
Required properties:
- ranges : Describes the translation of system controller addresses
for memory mapped registers.
- clock-frequency: Contains the main clock frequency for the system
controller chip.
- reg : This property defines the address and size of the
memory-mapped registers contained within the system controller
chip. The address specified in the "reg" property should match
the unit address of the system-controller node.
- #address-cells : Address representation for system controller
devices. This field represents the number of cells needed to
represent the address of the memory-mapped registers of devices
within the system controller chip.
- #size-cells : Size representation for for the memory-mapped
registers within the system controller chip.
- #interrupt-cells : Defines the width of cells used to represent
interrupts.
Optional properties:
- model : The specific model of the system controller chip. Such
as, "mv64360", "mv64460", or "mv64560".
- compatible : A string identifying the compatibility identifiers
of the system controller chip.
The system-controller node contains child nodes for each system
controller device that the platform uses. Nodes should not be created
for devices which exist on the system controller chip but are not used
Example Marvell Discovery mv64360 system-controller node:
system-controller@f1000000 { /* Marvell Discovery mv64360 */
#address-cells = <1>;
#size-cells = <1>;
model = "mv64360"; /* Default */
compatible = "marvell,mv64360";
clock-frequency = <133333333>;
reg = <0xf1000000 0x10000>;
virtual-reg = <0xf1000000>;
ranges = <0x88000000 0x88000000 0x1000000 /* PCI 0 I/O Space */
0x80000000 0x80000000 0x8000000 /* PCI 0 MEM Space */
0xa0000000 0xa0000000 0x4000000 /* User FLASH */
0x00000000 0xf1000000 0x0010000 /* Bridge's regs */
0xf2000000 0xf2000000 0x0040000>;/* Integrated SRAM */
[ child node definitions... ]
}
2) Child nodes of /system-controller
a) Marvell Discovery MDIO bus
The MDIO is a bus to which the PHY devices are connected. For each
device that exists on this bus, a child node should be created. See
the definition of the PHY node below for an example of how to define
a PHY.
Required properties:
- #address-cells : Should be <1>
- #size-cells : Should be <0>
- device_type : Should be "mdio"
- compatible : Should be "marvell,mv64360-mdio"
Example:
mdio {
#address-cells = <1>;
#size-cells = <0>;
device_type = "mdio";
compatible = "marvell,mv64360-mdio";
ethernet-phy@0 {
......
};
};
b) Marvell Discovery ethernet controller
The Discover ethernet controller is described with two levels
of nodes. The first level describes an ethernet silicon block
and the second level describes up to 3 ethernet nodes within
that block. The reason for the multiple levels is that the
registers for the node are interleaved within a single set
of registers. The "ethernet-block" level describes the
shared register set, and the "ethernet" nodes describe ethernet
port-specific properties.
Ethernet block node
Required properties:
- #address-cells : <1>
- #size-cells : <0>
- compatible : "marvell,mv64360-eth-block"
- reg : Offset and length of the register set for this block
Example Discovery Ethernet block node:
ethernet-block@2000 {
#address-cells = <1>;
#size-cells = <0>;
compatible = "marvell,mv64360-eth-block";
reg = <0x2000 0x2000>;
ethernet@0 {
.......
};
};
Ethernet port node
Required properties:
- device_type : Should be "network".
- compatible : Should be "marvell,mv64360-eth".
- reg : Should be <0>, <1>, or <2>, according to which registers
within the silicon block the device uses.
- interrupts : <a> where a is the interrupt number for the port.
- interrupt-parent : the phandle for the interrupt controller
that services interrupts for this device.
- phy : the phandle for the PHY connected to this ethernet
controller.
- local-mac-address : 6 bytes, MAC address
Example Discovery Ethernet port node:
ethernet@0 {
device_type = "network";
compatible = "marvell,mv64360-eth";
reg = <0>;
interrupts = <32>;
interrupt-parent = <&PIC>;
phy = <&PHY0>;
local-mac-address = [ 00 00 00 00 00 00 ];
};
c) Marvell Discovery PHY nodes
Required properties:
- device_type : Should be "ethernet-phy"
- interrupts : <a> where a is the interrupt number for this phy.
- interrupt-parent : the phandle for the interrupt controller that
services interrupts for this device.
- reg : The ID number for the phy, usually a small integer
Example Discovery PHY node:
ethernet-phy@1 {
device_type = "ethernet-phy";
compatible = "broadcom,bcm5421";
interrupts = <76>; /* GPP 12 */
interrupt-parent = <&PIC>;
reg = <1>;
};
d) Marvell Discovery SDMA nodes
Represent DMA hardware associated with the MPSC (multiprotocol
serial controllers).
Required properties:
- compatible : "marvell,mv64360-sdma"
- reg : Offset and length of the register set for this device
- interrupts : <a> where a is the interrupt number for the DMA
device.
- interrupt-parent : the phandle for the interrupt controller
that services interrupts for this device.
Example Discovery SDMA node:
sdma@4000 {
compatible = "marvell,mv64360-sdma";
reg = <0x4000 0xc18>;
virtual-reg = <0xf1004000>;
interrupts = <36>;
interrupt-parent = <&PIC>;
};
e) Marvell Discovery BRG nodes
Represent baud rate generator hardware associated with the MPSC
(multiprotocol serial controllers).
Required properties:
- compatible : "marvell,mv64360-brg"
- reg : Offset and length of the register set for this device
- clock-src : A value from 0 to 15 which selects the clock
source for the baud rate generator. This value corresponds
to the CLKS value in the BRGx configuration register. See
the mv64x60 User's Manual.
- clock-frequence : The frequency (in Hz) of the baud rate
generator's input clock.
- current-speed : The current speed setting (presumably by
firmware) of the baud rate generator.
Example Discovery BRG node:
brg@b200 {
compatible = "marvell,mv64360-brg";
reg = <0xb200 0x8>;
clock-src = <8>;
clock-frequency = <133333333>;
current-speed = <9600>;
};
f) Marvell Discovery CUNIT nodes
Represent the Serial Communications Unit device hardware.
Required properties:
- reg : Offset and length of the register set for this device
Example Discovery CUNIT node:
cunit@f200 {
reg = <0xf200 0x200>;
};
g) Marvell Discovery MPSCROUTING nodes
Represent the Discovery's MPSC routing hardware
Required properties:
- reg : Offset and length of the register set for this device
Example Discovery CUNIT node:
mpscrouting@b500 {
reg = <0xb400 0xc>;
};
h) Marvell Discovery MPSCINTR nodes
Represent the Discovery's MPSC DMA interrupt hardware registers
(SDMA cause and mask registers).
Required properties:
- reg : Offset and length of the register set for this device
Example Discovery MPSCINTR node:
mpsintr@b800 {
reg = <0xb800 0x100>;
};
i) Marvell Discovery MPSC nodes
Represent the Discovery's MPSC (Multiprotocol Serial Controller)
serial port.
Required properties:
- device_type : "serial"
- compatible : "marvell,mv64360-mpsc"
- reg : Offset and length of the register set for this device
- sdma : the phandle for the SDMA node used by this port
- brg : the phandle for the BRG node used by this port
- cunit : the phandle for the CUNIT node used by this port
- mpscrouting : the phandle for the MPSCROUTING node used by this port
- mpscintr : the phandle for the MPSCINTR node used by this port
- cell-index : the hardware index of this cell in the MPSC core
- max_idle : value needed for MPSC CHR3 (Maximum Frame Length)
register
- interrupts : <a> where a is the interrupt number for the MPSC.
- interrupt-parent : the phandle for the interrupt controller
that services interrupts for this device.
Example Discovery MPSCINTR node:
mpsc@8000 {
device_type = "serial";
compatible = "marvell,mv64360-mpsc";
reg = <0x8000 0x38>;
virtual-reg = <0xf1008000>;
sdma = <&SDMA0>;
brg = <&BRG0>;
cunit = <&CUNIT>;
mpscrouting = <&MPSCROUTING>;
mpscintr = <&MPSCINTR>;
cell-index = <0>;
max_idle = <40>;
interrupts = <40>;
interrupt-parent = <&PIC>;
};
j) Marvell Discovery Watch Dog Timer nodes
Represent the Discovery's watchdog timer hardware
Required properties:
- compatible : "marvell,mv64360-wdt"
- reg : Offset and length of the register set for this device
Example Discovery Watch Dog Timer node:
wdt@b410 {
compatible = "marvell,mv64360-wdt";
reg = <0xb410 0x8>;
};
k) Marvell Discovery I2C nodes
Represent the Discovery's I2C hardware
Required properties:
- device_type : "i2c"
- compatible : "marvell,mv64360-i2c"
- reg : Offset and length of the register set for this device
- interrupts : <a> where a is the interrupt number for the I2C.
- interrupt-parent : the phandle for the interrupt controller
that services interrupts for this device.
Example Discovery I2C node:
compatible = "marvell,mv64360-i2c";
reg = <0xc000 0x20>;
virtual-reg = <0xf100c000>;
interrupts = <37>;
interrupt-parent = <&PIC>;
};
l) Marvell Discovery PIC (Programmable Interrupt Controller) nodes
Represent the Discovery's PIC hardware
Required properties:
- #interrupt-cells : <1>
- #address-cells : <0>
- compatible : "marvell,mv64360-pic"
- reg : Offset and length of the register set for this device
- interrupt-controller
Example Discovery PIC node:
pic {
#interrupt-cells = <1>;
#address-cells = <0>;
compatible = "marvell,mv64360-pic";
reg = <0x0 0x88>;
interrupt-controller;
};
m) Marvell Discovery MPP (Multipurpose Pins) multiplexing nodes
Represent the Discovery's MPP hardware
Required properties:
- compatible : "marvell,mv64360-mpp"
- reg : Offset and length of the register set for this device
Example Discovery MPP node:
mpp@f000 {
compatible = "marvell,mv64360-mpp";
reg = <0xf000 0x10>;
};
n) Marvell Discovery GPP (General Purpose Pins) nodes
Represent the Discovery's GPP hardware
Required properties:
- compatible : "marvell,mv64360-gpp"
- reg : Offset and length of the register set for this device
Example Discovery GPP node:
gpp@f000 {
compatible = "marvell,mv64360-gpp";
reg = <0xf100 0x20>;
};
o) Marvell Discovery PCI host bridge node
Represents the Discovery's PCI host bridge device. The properties
for this node conform to Rev 2.1 of the PCI Bus Binding to IEEE
1275-1994. A typical value for the compatible property is
"marvell,mv64360-pci".
Example Discovery PCI host bridge node
pci@80000000 {
#address-cells = <3>;
#size-cells = <2>;
#interrupt-cells = <1>;
device_type = "pci";
compatible = "marvell,mv64360-pci";
reg = <0xcf8 0x8>;
ranges = <0x01000000 0x0 0x0
0x88000000 0x0 0x01000000
0x02000000 0x0 0x80000000
0x80000000 0x0 0x08000000>;
bus-range = <0 255>;
clock-frequency = <66000000>;
interrupt-parent = <&PIC>;
interrupt-map-mask = <0xf800 0x0 0x0 0x7>;
interrupt-map = <
/* IDSEL 0x0a */
0x5000 0 0 1 &PIC 80
0x5000 0 0 2 &PIC 81
0x5000 0 0 3 &PIC 91
0x5000 0 0 4 &PIC 93
/* IDSEL 0x0b */
0x5800 0 0 1 &PIC 91
0x5800 0 0 2 &PIC 93
0x5800 0 0 3 &PIC 80
0x5800 0 0 4 &PIC 81
/* IDSEL 0x0c */
0x6000 0 0 1 &PIC 91
0x6000 0 0 2 &PIC 93
0x6000 0 0 3 &PIC 80
0x6000 0 0 4 &PIC 81
/* IDSEL 0x0d */
0x6800 0 0 1 &PIC 93
0x6800 0 0 2 &PIC 80
0x6800 0 0 3 &PIC 81
0x6800 0 0 4 &PIC 91
>;
};
p) Marvell Discovery CPU Error nodes
Represent the Discovery's CPU error handler device.
Required properties:
- compatible : "marvell,mv64360-cpu-error"
- reg : Offset and length of the register set for this device
- interrupts : the interrupt number for this device
- interrupt-parent : the phandle for the interrupt controller
that services interrupts for this device.
Example Discovery CPU Error node:
cpu-error@0070 {
compatible = "marvell,mv64360-cpu-error";
reg = <0x70 0x10 0x128 0x28>;
interrupts = <3>;
interrupt-parent = <&PIC>;
};
q) Marvell Discovery SRAM Controller nodes
Represent the Discovery's SRAM controller device.
Required properties:
- compatible : "marvell,mv64360-sram-ctrl"
- reg : Offset and length of the register set for this device
- interrupts : the interrupt number for this device
- interrupt-parent : the phandle for the interrupt controller
that services interrupts for this device.
Example Discovery SRAM Controller node:
sram-ctrl@0380 {
compatible = "marvell,mv64360-sram-ctrl";
reg = <0x380 0x80>;
interrupts = <13>;
interrupt-parent = <&PIC>;
};
r) Marvell Discovery PCI Error Handler nodes
Represent the Discovery's PCI error handler device.
Required properties:
- compatible : "marvell,mv64360-pci-error"
- reg : Offset and length of the register set for this device
- interrupts : the interrupt number for this device
- interrupt-parent : the phandle for the interrupt controller
that services interrupts for this device.
Example Discovery PCI Error Handler node:
pci-error@1d40 {
compatible = "marvell,mv64360-pci-error";
reg = <0x1d40 0x40 0xc28 0x4>;
interrupts = <12>;
interrupt-parent = <&PIC>;
};
s) Marvell Discovery Memory Controller nodes
Represent the Discovery's memory controller device.
Required properties:
- compatible : "marvell,mv64360-mem-ctrl"
- reg : Offset and length of the register set for this device
- interrupts : the interrupt number for this device
- interrupt-parent : the phandle for the interrupt controller
that services interrupts for this device.
Example Discovery Memory Controller node:
mem-ctrl@1400 {
compatible = "marvell,mv64360-mem-ctrl";
reg = <0x1400 0x60>;
interrupts = <17>;
interrupt-parent = <&PIC>;
};
VIII - Specifying interrupt information for devices
===================================================
The device tree represents the busses and devices of a hardware
system in a form similar to the physical bus topology of the
hardware.
In addition, a logical 'interrupt tree' exists which represents the
hierarchy and routing of interrupts in the hardware.
The interrupt tree model is fully described in the
document "Open Firmware Recommended Practice: Interrupt
Mapping Version 0.9". The document is available at:
<http://playground.sun.com/1275/practice>.
1) interrupts property
----------------------
Devices that generate interrupts to a single interrupt controller
should use the conventional OF representation described in the
OF interrupt mapping documentation.
Each device which generates interrupts must have an 'interrupt'
property. The interrupt property value is an arbitrary number of
of 'interrupt specifier' values which describe the interrupt or
interrupts for the device.
The encoding of an interrupt specifier is determined by the
interrupt domain in which the device is located in the
interrupt tree. The root of an interrupt domain specifies in
its #interrupt-cells property the number of 32-bit cells
required to encode an interrupt specifier. See the OF interrupt
mapping documentation for a detailed description of domains.
For example, the binding for the OpenPIC interrupt controller
specifies an #interrupt-cells value of 2 to encode the interrupt
number and level/sense information. All interrupt children in an
OpenPIC interrupt domain use 2 cells per interrupt in their interrupts
property.
The PCI bus binding specifies a #interrupt-cell value of 1 to encode
which interrupt pin (INTA,INTB,INTC,INTD) is used.
2) interrupt-parent property
----------------------------
The interrupt-parent property is specified to define an explicit
link between a device node and its interrupt parent in
the interrupt tree. The value of interrupt-parent is the
phandle of the parent node.
If the interrupt-parent property is not defined for a node, it's
interrupt parent is assumed to be an ancestor in the node's
_device tree_ hierarchy.
3) OpenPIC Interrupt Controllers
--------------------------------
OpenPIC interrupt controllers require 2 cells to encode
interrupt information. The first cell defines the interrupt
number. The second cell defines the sense and level
information.
Sense and level information should be encoded as follows:
0 = low to high edge sensitive type enabled
1 = active low level sensitive type enabled
2 = active high level sensitive type enabled
3 = high to low edge sensitive type enabled
4) ISA Interrupt Controllers
----------------------------
ISA PIC interrupt controllers require 2 cells to encode
interrupt information. The first cell defines the interrupt
number. The second cell defines the sense and level
information.
ISA PIC interrupt controllers should adhere to the ISA PIC
encodings listed below:
0 = active low level sensitive type enabled
1 = active high level sensitive type enabled
2 = high to low edge sensitive type enabled
3 = low to high edge sensitive type enabled
IX - Specifying GPIO information for devices
============================================
1) gpios property
-----------------
Nodes that makes use of GPIOs should define them using `gpios' property,
format of which is: <&gpio-controller1-phandle gpio1-specifier
&gpio-controller2-phandle gpio2-specifier
0 /* holes are permitted, means no GPIO 3 */
&gpio-controller4-phandle gpio4-specifier
...>;
Note that gpio-specifier length is controller dependent.
gpio-specifier may encode: bank, pin position inside the bank,
whether pin is open-drain and whether pin is logically inverted.
Example of the node using GPIOs:
node {
gpios = <&qe_pio_e 18 0>;
};
In this example gpio-specifier is "18 0" and encodes GPIO pin number,
and empty GPIO flags as accepted by the "qe_pio_e" gpio-controller.
2) gpio-controller nodes
------------------------
Every GPIO controller node must have #gpio-cells property defined,
this information will be used to translate gpio-specifiers.
Example of two SOC GPIO banks defined as gpio-controller nodes:
qe_pio_a: gpio-controller@1400 {
#gpio-cells = <2>;
compatible = "fsl,qe-pario-bank-a", "fsl,qe-pario-bank";
reg = <0x1400 0x18>;
gpio-controller;
};
qe_pio_e: gpio-controller@1460 {
#gpio-cells = <2>;
compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank";
reg = <0x1460 0x18>;
gpio-controller;
};
X - Specifying Device Power Management Information (sleep property)
===================================================================
Devices on SOCs often have mechanisms for placing devices into low-power
states that are decoupled from the devices' own register blocks. Sometimes,
this information is more complicated than a cell-index property can
reasonably describe. Thus, each device controlled in such a manner
may contain a "sleep" property which describes these connections.
The sleep property consists of one or more sleep resources, each of
which consists of a phandle to a sleep controller, followed by a
controller-specific sleep specifier of zero or more cells.
The semantics of what type of low power modes are possible are defined
by the sleep controller. Some examples of the types of low power modes
that may be supported are:
- Dynamic: The device may be disabled or enabled at any time.
- System Suspend: The device may request to be disabled or remain
awake during system suspend, but will not be disabled until then.
- Permanent: The device is disabled permanently (until the next hard
reset).
Some devices may share a clock domain with each other, such that they should
only be suspended when none of the devices are in use. Where reasonable,
such nodes should be placed on a virtual bus, where the bus has the sleep
property. If the clock domain is shared among devices that cannot be
reasonably grouped in this manner, then create a virtual sleep controller
(similar to an interrupt nexus, except that defining a standardized
sleep-map should wait until its necessity is demonstrated).
Appendix A - Sample SOC node for MPC8540
========================================
soc@e0000000 {
#address-cells = <1>;
#size-cells = <1>;
compatible = "fsl,mpc8540-ccsr", "simple-bus";
device_type = "soc";
ranges = <0x00000000 0xe0000000 0x00100000>
bus-frequency = <0>;
interrupt-parent = <&pic>;
ethernet@24000 {
#address-cells = <1>;
#size-cells = <1>;
device_type = "network";
model = "TSEC";
compatible = "gianfar", "simple-bus";
reg = <0x24000 0x1000>;
local-mac-address = [ 00 E0 0C 00 73 00 ];
interrupts = <29 2 30 2 34 2>;
phy-handle = <&phy0>;
sleep = <&pmc 00000080>;
ranges;
mdio@24520 {
reg = <0x24520 0x20>;
compatible = "fsl,gianfar-mdio";
phy0: ethernet-phy@0 {
interrupts = <5 1>;
reg = <0>;
device_type = "ethernet-phy";
};
phy1: ethernet-phy@1 {
interrupts = <5 1>;
reg = <1>;
device_type = "ethernet-phy";
};
phy3: ethernet-phy@3 {
interrupts = <7 1>;
reg = <3>;
device_type = "ethernet-phy";
};
};
};
ethernet@25000 {
device_type = "network";
model = "TSEC";
compatible = "gianfar";
reg = <0x25000 0x1000>;
local-mac-address = [ 00 E0 0C 00 73 01 ];
interrupts = <13 2 14 2 18 2>;
phy-handle = <&phy1>;
sleep = <&pmc 00000040>;
};
ethernet@26000 {
device_type = "network";
model = "FEC";
compatible = "gianfar";
reg = <0x26000 0x1000>;
local-mac-address = [ 00 E0 0C 00 73 02 ];
interrupts = <41 2>;
phy-handle = <&phy3>;
sleep = <&pmc 00000020>;
};
serial@4500 {
#address-cells = <1>;
#size-cells = <1>;
compatible = "fsl,mpc8540-duart", "simple-bus";
sleep = <&pmc 00000002>;
ranges;
serial@4500 {
device_type = "serial";
compatible = "ns16550";
reg = <0x4500 0x100>;
clock-frequency = <0>;
interrupts = <42 2>;
};
serial@4600 {
device_type = "serial";
compatible = "ns16550";
reg = <0x4600 0x100>;
clock-frequency = <0>;
interrupts = <42 2>;
};
};
pic: pic@40000 {
interrupt-controller;
#address-cells = <0>;
#interrupt-cells = <2>;
reg = <0x40000 0x40000>;
compatible = "chrp,open-pic";
device_type = "open-pic";
};
i2c@3000 {
interrupts = <43 2>;
reg = <0x3000 0x100>;
compatible = "fsl-i2c";
dfsrr;
sleep = <&pmc 00000004>;
};
pmc: power@e0070 {
compatible = "fsl,mpc8540-pmc", "fsl,mpc8548-pmc";
reg = <0xe0070 0x20>;
};
};
