path: root/Documentation/arm/Porting
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authorLinus Torvalds <>2005-04-16 15:20:36 -0700
committerLinus Torvalds <>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/arm/Porting
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+Taken from list archive at
+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
+ 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.
+ 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.
+ 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.
+ 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).
+ Virtual address of the initial RAM disk. The following constraint
+ must be valid:
+ __virt_to_phys(INITRD_VIRT) == INITRD_PHYS
+ Physical address of the struct param_struct or tag list, giving the
+ kernel various parameters about its execution environment.
+Kernel Symbols
+ Physical start address of the first bank of RAM.
+ 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.
+ 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).
+ 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.
+ Virtual address for the kernel data segment. Must not be defined
+ when using the decompressor.
+ 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).
+ 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
+ `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).
+ Same as, and see PARAMS_PHYS.
+ Machine specific fixups, run before memory subsystems have been
+ initialised.
+ Machine specific function to map IO areas (including the debug
+ region above).
+ Machine specific function to initialise interrupts.