[POWERPC] 85xx: Add support for relocatable kernel (and booting at non-zero)

Added support to allow an 85xx kernel to be run from a non-zero physical
address (useful for cooperative asymmetric multiprocessing situations and
kdump).  The support can be configured at compile time by setting
CONFIG_PAGE_OFFSET, CONFIG_KERNEL_START, and CONFIG_PHYSICAL_START as
desired.

Alternatively, the kernel build can set CONFIG_RELOCATABLE.  Setting this
config option causes the kernel to determine at runtime the physical
addresses of CONFIG_PAGE_OFFSET and CONFIG_KERNEL_START.  If
CONFIG_RELOCATABLE is set, then CONFIG_PHYSICAL_START has no meaning.
However, CONFIG_PHYSICAL_START will always be used to set the LOAD program
header physical address field in the resulting ELF image.

Currently we are limited to running at a physical address that is a
multiple of 256M.  This is due to how we map TLBs to cover
lowmem.  This should be fixed to allow 64M or maybe even 16M alignment
in the future.  It is considered an error to try and run a kernel at a
non-aligned physical address.

All the magic for this support is accomplished by proper initialization
of the kernel memory subsystem and use of ARCH_PFN_OFFSET.

The use of ARCH_PFN_OFFSET only affects normal memory and not IO mappings.
ioremap uses map_page and isn't affected by ARCH_PFN_OFFSET.

/dev/mem continues to allow access to any physical address in the system
regardless of how CONFIG_PHYSICAL_START is set.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 66 insertions, 3 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 4bb2e9310a56..fdc755a05f70 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -656,21 +656,76 @@ config LOWMEM_SIZE
         hex "Maximum low memory size (in bytes)" if LOWMEM_SIZE_BOOL
         default "0x30000000"
 
+config RELOCATABLE
+        bool "Build a relocatable kernel (EXPERIMENTAL)"
+        depends on EXPERIMENTAL && ADVANCED_OPTIONS && FLATMEM && FSL_BOOKE
+        help
+          This builds a kernel image that is capable of running at the
+          location the kernel is loaded at (some alignment restrictions may
+          exist).
+
+          One use is for the kexec on panic case where the recovery kernel
+          must live at a different physical address than the primary
+          kernel.
+
+          Note: If CONFIG_RELOCATABLE=y, then the kernel runs from the address
+          it has been loaded at and the compile time physical addresses
+          CONFIG_PHYSICAL_START is ignored.  However CONFIG_PHYSICAL_START
+          setting can still be useful to bootwrappers that need to know the
+          load location of the kernel (eg. u-boot/mkimage).
+
+config PAGE_OFFSET_BOOL
+        bool "Set custom page offset address"
+        depends on ADVANCED_OPTIONS
+        help
+          This option allows you to set the kernel virtual address at which
+          the kernel will map low memory.  This can be useful in optimizing
+          the virtual memory layout of the system.
+
+          Say N here unless you know what you are doing.
+
+config PAGE_OFFSET
+        hex "Virtual address of memory base" if PAGE_OFFSET_BOOL
+        default "0xc0000000"
+
 config KERNEL_START_BOOL
         bool "Set custom kernel base address"
         depends on ADVANCED_OPTIONS
         help
           This option allows you to set the kernel virtual address at which
-          the kernel will map low memory (the kernel image will be linked at
-          this address).  This can be useful in optimizing the virtual memory
-          layout of the system.
+          the kernel will be loaded.  Normally this should match PAGE_OFFSET
+          however there are times (like kdump) that one might not want them
+          to be the same.
 
           Say N here unless you know what you are doing.
 
 config KERNEL_START
         hex "Virtual address of kernel base" if KERNEL_START_BOOL
+        default PAGE_OFFSET if PAGE_OFFSET_BOOL
+        default "0xc2000000" if CRASH_DUMP
         default "0xc0000000"
 
+config PHYSICAL_START_BOOL
+        bool "Set physical address where the kernel is loaded"
+        depends on ADVANCED_OPTIONS && FLATMEM && FSL_BOOKE
+        help
+          This gives the physical address where the kernel is loaded.
+
+          Say N here unless you know what you are doing.
+
+config PHYSICAL_START
+        hex "Physical address where the kernel is loaded" if PHYSICAL_START_BOOL
+        default "0x02000000" if PPC_STD_MMU && CRASH_DUMP
+        default "0x00000000"
+
+config PHYSICAL_ALIGN
+        hex
+        default "0x10000000" if FSL_BOOKE
+        help
+          This value puts the alignment restrictions on physical address
+          where kernel is loaded and run from. Kernel is compiled for an
+          address which meets above alignment restriction.
+
 config TASK_SIZE_BOOL
         bool "Set custom user task size"
         depends on ADVANCED_OPTIONS
@@ -717,9 +772,17 @@ config PIN_TLB
 endmenu
 
 if PPC64
+config PAGE_OFFSET
+        hex
+        default "0xc000000000000000"
 config KERNEL_START
         hex
+        default "0xc000000002000000" if CRASH_DUMP
         default "0xc000000000000000"
+config PHYSICAL_START
+        hex
+        default "0x02000000" if CRASH_DUMP
+        default "0x00000000"
 endif
 
 source "net/Kconfig"