[ARM PATCH] 1473/1: Add Russell's porting information to Documentation

Patch from Eli Carter

# Tue Apr  1 11:50:11 CST 2003
# Grab a copy of Russell's information on important porting information and
# stick it in the Documentation/arm directory where people will find it before
# posting to the lists.
#
# Patch is against 2.5.65-rmk1
#
# Documentation/arm/Porting |  135 ++++++++++++++++++++++++++++++++++++++++++++++
# 1 files changed, 135 insertions(+)
#

Documentation/arm/Porting

+Taken from list archive at http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2001-July/004064.html
+
+Initial definitions
+-------------------
+
+The following symbol definitions rely on you knowing the translation that
+__virt_to_phys() does for your machine.  This macro converts the passed
+virtual address to a physical address.  Normally, it is simply:
+
+		phys = virt - PAGE_OFFSET + PHYS_OFFSET
+
+
+Decompressor Symbols
+--------------------
+
+ZTEXTADDR
+	Start address of decompressor.  There's no point in talking about
+	virtual or physical addresses here, since the MMU will be off at
+	the time when you call the decompressor code.  You normally call
+	the kernel at this address to start it booting.  This doesn't have
+	to be located in RAM, it can be in flash or other read-only or
+	read-write addressable medium.
+
+ZBSSADDR
+	Start address of zero-initialised work area for the decompressor.
+	This must be pointing at RAM.  The decompressor will zero initialise
+	this for you.  Again, the MMU will be off.
+
+ZRELADDR
+	This is the address where the decompressed kernel will be written,
+	and eventually executed.  The following constraint must be valid:
+
+		__virt_to_phys(TEXTADDR) == ZRELADDR
+
+	The initial part of the kernel is carefully coded to be position
+	independent.
+
+INITRD_PHYS
+	Physical address to place the initial RAM disk.  Only relevant if
+	you are using the bootpImage stuff (which only works on the old
+	struct param_struct).
+
+INITRD_VIRT
+	Virtual address of the initial RAM disk.  The following  constraint
+	must be valid:
+
+		__virt_to_phys(INITRD_VIRT) == INITRD_PHYS
+
+PARAMS_PHYS
+	Physical address of the struct param_struct or tag list, giving the
+	kernel various parameters about its execution environment.
+
+
+Kernel Symbols
+--------------
+
+PHYS_OFFSET
+	Physical start address of the first bank of RAM.
+
+PAGE_OFFSET
+	Virtual start address of the first bank of RAM.  During the kernel
+	boot phase, virtual address PAGE_OFFSET will be mapped to physical
+	address PHYS_OFFSET, along with any other mappings you supply.
+	This should be the same value as TASK_SIZE.
+
+TASK_SIZE
+	The maximum size of a user process in bytes.  Since user space
+	always starts at zero, this is the maximum address that a user
+	process can access+1.  The user space stack grows down from this
+	address.
+
+	Any virtual address below TASK_SIZE is deemed to be user process
+	area, and therefore managed dynamically on a process by process
+	basis by the kernel.  I'll call this the user segment.
+
+	Anything above TASK_SIZE is common to all processes.  I'll call
+	this the kernel segment.
+
+	(In other words, you can't put IO mappings below TASK_SIZE, and
+	hence PAGE_OFFSET).
+
+TEXTADDR
+	Virtual start address of kernel, normally PAGE_OFFSET + 0x8000.
+	This is where the kernel image ends up.  With the latest kernels,
+	it must be located at 32768 bytes into a 128MB region.  Previous
+	kernels placed a restriction of 256MB here.
+
+DATAADDR
+	Virtual address for the kernel data segment.  Must not be defined
+	when using the decompressor.
+
+VMALLOC_START
+VMALLOC_END
+	Virtual addresses bounding the vmalloc() area.  There must not be
+	any static mappings in this area; vmalloc will overwrite them.
+	The addresses must also be in the kernel segment (see above).
+	Normally, the vmalloc() area starts VMALLOC_OFFSET bytes above the
+	last virtual RAM address (found using variable high_memory).
+
+VMALLOC_OFFSET
+	Offset normally incorporated into VMALLOC_START to provide a hole
+	between virtual RAM and the vmalloc area.  We do this to allow
+	out of bounds memory accesses (eg, something writing off the end
+	of the mapped memory map) to be caught.  Normally set to 8MB.
+
+Architecture Specific Macros
+----------------------------
+
+BOOT_MEM(pram,pio,vio)
+	`pram' specifies the physical start address of RAM.  Must always
+	be present, and should be the same as PHYS_OFFSET.
+
+	`pio' is the physical address of an 8MB region containing IO for
+	use with the debugging macros in arch/arm/kernel/debug-armv.S.
+
+	`vio' is the virtual address of the 8MB debugging region.
+
+	It is expected that the debugging region will be re-initialised
+	by the architecture specific code later in the code (via the
+	MAPIO function).
+
+BOOT_PARAMS
+	Same as, and see PARAMS_PHYS.
+
+FIXUP(func)
+	Machine specific fixups, run before memory subsystems have been
+	initialised.
+
+MAPIO(func)
+	Machine specific function to map IO areas (including the debug
+	region above).
+
+INITIRQ(func)
+	Machine specific function to initialise interrupts.
+