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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
<book id="libataDevGuide">
<bookinfo>
<title>libATA Developer's Guide</title>
<authorgroup>
<author>
<firstname>Jeff</firstname>
<surname>Garzik</surname>
</author>
</authorgroup>
<copyright>
<year>2003-2005</year>
<holder>Jeff Garzik</holder>
</copyright>
<legalnotice>
<para>
The contents of this file are subject to the Open
Software License version 1.1 that can be found at
<ulink url="http://www.opensource.org/licenses/osl-1.1.txt">http://www.opensource.org/licenses/osl-1.1.txt</ulink> and is included herein
by reference.
</para>
<para>
Alternatively, the contents of this file may be used under the terms
of the GNU General Public License version 2 (the "GPL") as distributed
in the kernel source COPYING file, in which case the provisions of
the GPL are applicable instead of the above. If you wish to allow
the use of your version of this file only under the terms of the
GPL and not to allow others to use your version of this file under
the OSL, indicate your decision by deleting the provisions above and
replace them with the notice and other provisions required by the GPL.
If you do not delete the provisions above, a recipient may use your
version of this file under either the OSL or the GPL.
</para>
</legalnotice>
</bookinfo>
<toc></toc>
<chapter id="libataIntroduction">
<title>Introduction</title>
<para>
libATA is a library used inside the Linux kernel to support ATA host
controllers and devices. libATA provides an ATA driver API, class
transports for ATA and ATAPI devices, and SCSI<->ATA translation
for ATA devices according to the T10 SAT specification.
</para>
<para>
This Guide documents the libATA driver API, library functions, library
internals, and a couple sample ATA low-level drivers.
</para>
</chapter>
<chapter id="libataDriverApi">
<title>libata Driver API</title>
<para>
struct ata_port_operations is defined for every low-level libata
hardware driver, and it controls how the low-level driver
interfaces with the ATA and SCSI layers.
</para>
<para>
FIS-based drivers will hook into the system with ->qc_prep() and
->qc_issue() high-level hooks. Hardware which behaves in a manner
similar to PCI IDE hardware may utilize several generic helpers,
defining at a bare minimum the bus I/O addresses of the ATA shadow
register blocks.
</para>
<sect1>
<title>struct ata_port_operations</title>
<sect2><title>Disable ATA port</title>
<programlisting>
void (*port_disable) (struct ata_port *);
</programlisting>
<para>
Called from ata_bus_probe() and ata_bus_reset() error paths,
as well as when unregistering from the SCSI module (rmmod, hot
unplug).
</para>
</sect2>
<sect2><title>Post-IDENTIFY device configuration</title>
<programlisting>
void (*dev_config) (struct ata_port *, struct ata_device *);
</programlisting>
<para>
Called after IDENTIFY [PACKET] DEVICE is issued to each device
found. Typically used to apply device-specific fixups prior to
issue of SET FEATURES - XFER MODE, and prior to operation.
</para>
</sect2>
<sect2><title>Set PIO/DMA mode</title>
<programlisting>
void (*set_piomode) (struct ata_port *, struct ata_device *);
void (*set_dmamode) (struct ata_port *, struct ata_device *);
void (*post_set_mode) (struct ata_port *ap);
</programlisting>
<para>
Hooks called prior to the issue of SET FEATURES - XFER MODE
command. dev->pio_mode is guaranteed to be valid when
->set_piomode() is called, and dev->dma_mode is guaranteed to be
valid when ->set_dmamode() is called. ->post_set_mode() is
called unconditionally, after the SET FEATURES - XFER MODE
command completes successfully.
</para>
<para>
->set_piomode() is always called (if present), but
->set_dma_mode() is only called if DMA is possible.
</para>
</sect2>
<sect2><title>Taskfile read/write</title>
<programlisting>
void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
</programlisting>
<para>
->tf_load() is called to load the given taskfile into hardware
registers / DMA buffers. ->tf_read() is called to read the
hardware registers / DMA buffers, to obtain the current set of
taskfile register values.
</para>
</sect2>
<sect2><title>ATA command execute</title>
<programlisting>
void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
</programlisting>
<para>
causes an ATA command, previously loaded with
->tf_load(), to be initiated in hardware.
</para>
</sect2>
<sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
<programlisting>
int (*check_atapi_dma) (struct ata_queued_cmd *qc);
</programlisting>
<para>
Allow low-level driver to filter ATA PACKET commands, returning a status
indicating whether or not it is OK to use DMA for the supplied PACKET
command.
</para>
</sect2>
<sect2><title>Read specific ATA shadow registers</title>
<programlisting>
u8 (*check_status)(struct ata_port *ap);
u8 (*check_altstatus)(struct ata_port *ap);
u8 (*check_err)(struct ata_port *ap);
</programlisting>
<para>
Reads the Status/AltStatus/Error ATA shadow register from
hardware. On some hardware, reading the Status register has
the side effect of clearing the interrupt condition.
</para>
</sect2>
<sect2><title>Select ATA device on bus</title>
<programlisting>
void (*dev_select)(struct ata_port *ap, unsigned int device);
</programlisting>
<para>
Issues the low-level hardware command(s) that causes one of N
hardware devices to be considered 'selected' (active and
available for use) on the ATA bus. This generally has no
meaning on FIS-based devices.
</para>
</sect2>
<sect2><title>Reset ATA bus</title>
<programlisting>
void (*phy_reset) (struct ata_port *ap);
</programlisting>
<para>
The very first step in the probe phase. Actions vary depending
on the bus type, typically. After waking up the device and probing
for device presence (PATA and SATA), typically a soft reset
(SRST) will be performed. Drivers typically use the helper
functions ata_bus_reset() or sata_phy_reset() for this hook.
</para>
</sect2>
<sect2><title>Control PCI IDE BMDMA engine</title>
<programlisting>
void (*bmdma_setup) (struct ata_queued_cmd *qc);
void (*bmdma_start) (struct ata_queued_cmd *qc);
void (*bmdma_stop) (struct ata_port *ap);
u8 (*bmdma_status) (struct ata_port *ap);
</programlisting>
<para>
When setting up an IDE BMDMA transaction, these hooks arm
(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
the hardware's DMA engine. ->bmdma_status is used to read the standard
PCI IDE DMA Status register.
</para>
<para>
These hooks are typically either no-ops, or simply not implemented, in
FIS-based drivers.
</para>
</sect2>
<sect2><title>High-level taskfile hooks</title>
<programlisting>
void (*qc_prep) (struct ata_queued_cmd *qc);
int (*qc_issue) (struct ata_queued_cmd *qc);
</programlisting>
<para>
Higher-level hooks, these two hooks can potentially supercede
several of the above taskfile/DMA engine hooks. ->qc_prep is
called after the buffers have been DMA-mapped, and is typically
used to populate the hardware's DMA scatter-gather table.
Most drivers use the standard ata_qc_prep() helper function, but
more advanced drivers roll their own.
</para>
<para>
->qc_issue is used to make a command active, once the hardware
and S/G tables have been prepared. IDE BMDMA drivers use the
helper function ata_qc_issue_prot() for taskfile protocol-based
dispatch. More advanced drivers implement their own ->qc_issue.
</para>
</sect2>
<sect2><title>Timeout (error) handling</title>
<programlisting>
void (*eng_timeout) (struct ata_port *ap);
</programlisting>
<para>
This is a high level error handling function, called from the
error handling thread, when a command times out. Most newer
hardware will implement its own error handling code here. IDE BMDMA
drivers may use the helper function ata_eng_timeout().
</para>
</sect2>
<sect2><title>Hardware interrupt handling</title>
<programlisting>
irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
void (*irq_clear) (struct ata_port *);
</programlisting>
<para>
->irq_handler is the interrupt handling routine registered with
the system, by libata. ->irq_clear is called during probe just
before the interrupt handler is registered, to be sure hardware
is quiet.
</para>
</sect2>
<sect2><title>SATA phy read/write</title>
<programlisting>
u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg);
void (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
u32 val);
</programlisting>
<para>
Read and write standard SATA phy registers. Currently only used
if ->phy_reset hook called the sata_phy_reset() helper function.
</para>
</sect2>
<sect2><title>Init and shutdown</title>
<programlisting>
int (*port_start) (struct ata_port *ap);
void (*port_stop) (struct ata_port *ap);
void (*host_stop) (struct ata_host_set *host_set);
</programlisting>
<para>
->port_start() is called just after the data structures for each
port are initialized. Typically this is used to alloc per-port
DMA buffers / tables / rings, enable DMA engines, and similar
tasks.
</para>
<para>
->port_stop() is called after ->host_stop(). It's sole function
is to release DMA/memory resources, now that they are no longer
actively being used.
</para>
<para>
->host_stop() is called after all ->port_stop() calls
have completed. The hook must finalize hardware shutdown, release DMA
and other resources, etc.
</para>
</sect2>
</sect1>
</chapter>
<chapter id="libataExt">
<title>libata Library</title>
!Edrivers/scsi/libata-core.c
</chapter>
<chapter id="libataInt">
<title>libata Core Internals</title>
!Idrivers/scsi/libata-core.c
</chapter>
<chapter id="libataScsiInt">
<title>libata SCSI translation/emulation</title>
!Edrivers/scsi/libata-scsi.c
!Idrivers/scsi/libata-scsi.c
</chapter>
<chapter id="PiixInt">
<title>ata_piix Internals</title>
!Idrivers/scsi/ata_piix.c
</chapter>
<chapter id="SILInt">
<title>sata_sil Internals</title>
!Idrivers/scsi/sata_sil.c
</chapter>
<chapter id="libataThanks">
<title>Thanks</title>
<para>
The bulk of the ATA knowledge comes thanks to long conversations with
Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
and SCSI specifications.
</para>
<para>
Thanks to Alan Cox for pointing out similarities
between SATA and SCSI, and in general for motivation to hack on
libata.
</para>
<para>
libata's device detection
method, ata_pio_devchk, and in general all the early probing was
based on extensive study of Hale Landis's probe/reset code in his
ATADRVR driver (www.ata-atapi.com).
</para>
</chapter>
</book>
