linux/Documentation/arm/Porting
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   1Taken from list archive at http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2001-July/004064.html
   2
   3Initial definitions
   4-------------------
   5
   6The following symbol definitions rely on you knowing the translation that
   7__virt_to_phys() does for your machine.  This macro converts the passed
   8virtual address to a physical address.  Normally, it is simply:
   9
  10                phys = virt - PAGE_OFFSET + PHYS_OFFSET
  11
  12
  13Decompressor Symbols
  14--------------------
  15
  16ZTEXTADDR
  17        Start address of decompressor.  There's no point in talking about
  18        virtual or physical addresses here, since the MMU will be off at
  19        the time when you call the decompressor code.  You normally call
  20        the kernel at this address to start it booting.  This doesn't have
  21        to be located in RAM, it can be in flash or other read-only or
  22        read-write addressable medium.
  23
  24ZBSSADDR
  25        Start address of zero-initialised work area for the decompressor.
  26        This must be pointing at RAM.  The decompressor will zero initialise
  27        this for you.  Again, the MMU will be off.
  28
  29ZRELADDR
  30        This is the address where the decompressed kernel will be written,
  31        and eventually executed.  The following constraint must be valid:
  32
  33                __virt_to_phys(TEXTADDR) == ZRELADDR
  34
  35        The initial part of the kernel is carefully coded to be position
  36        independent.
  37
  38INITRD_PHYS
  39        Physical address to place the initial RAM disk.  Only relevant if
  40        you are using the bootpImage stuff (which only works on the old
  41        struct param_struct).
  42
  43INITRD_VIRT
  44        Virtual address of the initial RAM disk.  The following  constraint
  45        must be valid:
  46
  47                __virt_to_phys(INITRD_VIRT) == INITRD_PHYS
  48
  49PARAMS_PHYS
  50        Physical address of the struct param_struct or tag list, giving the
  51        kernel various parameters about its execution environment.
  52
  53
  54Kernel Symbols
  55--------------
  56
  57PHYS_OFFSET
  58        Physical start address of the first bank of RAM.
  59
  60PAGE_OFFSET
  61        Virtual start address of the first bank of RAM.  During the kernel
  62        boot phase, virtual address PAGE_OFFSET will be mapped to physical
  63        address PHYS_OFFSET, along with any other mappings you supply.
  64        This should be the same value as TASK_SIZE.
  65
  66TASK_SIZE
  67        The maximum size of a user process in bytes.  Since user space
  68        always starts at zero, this is the maximum address that a user
  69        process can access+1.  The user space stack grows down from this
  70        address.
  71
  72        Any virtual address below TASK_SIZE is deemed to be user process
  73        area, and therefore managed dynamically on a process by process
  74        basis by the kernel.  I'll call this the user segment.
  75
  76        Anything above TASK_SIZE is common to all processes.  I'll call
  77        this the kernel segment.
  78
  79        (In other words, you can't put IO mappings below TASK_SIZE, and
  80        hence PAGE_OFFSET).
  81
  82TEXTADDR
  83        Virtual start address of kernel, normally PAGE_OFFSET + 0x8000.
  84        This is where the kernel image ends up.  With the latest kernels,
  85        it must be located at 32768 bytes into a 128MB region.  Previous
  86        kernels placed a restriction of 256MB here.
  87
  88DATAADDR
  89        Virtual address for the kernel data segment.  Must not be defined
  90        when using the decompressor.
  91
  92VMALLOC_START
  93VMALLOC_END
  94        Virtual addresses bounding the vmalloc() area.  There must not be
  95        any static mappings in this area; vmalloc will overwrite them.
  96        The addresses must also be in the kernel segment (see above).
  97        Normally, the vmalloc() area starts VMALLOC_OFFSET bytes above the
  98        last virtual RAM address (found using variable high_memory).
  99
 100VMALLOC_OFFSET
 101        Offset normally incorporated into VMALLOC_START to provide a hole
 102        between virtual RAM and the vmalloc area.  We do this to allow
 103        out of bounds memory accesses (eg, something writing off the end
 104        of the mapped memory map) to be caught.  Normally set to 8MB.
 105
 106Architecture Specific Macros
 107----------------------------
 108
 109BOOT_MEM(pram,pio,vio)
 110        `pram' specifies the physical start address of RAM.  Must always
 111        be present, and should be the same as PHYS_OFFSET.
 112
 113        `pio' is the physical address of an 8MB region containing IO for
 114        use with the debugging macros in arch/arm/kernel/debug-armv.S.
 115
 116        `vio' is the virtual address of the 8MB debugging region.
 117
 118        It is expected that the debugging region will be re-initialised
 119        by the architecture specific code later in the code (via the
 120        MAPIO function).
 121
 122BOOT_PARAMS
 123        Same as, and see PARAMS_PHYS.
 124
 125FIXUP(func)
 126        Machine specific fixups, run before memory subsystems have been
 127        initialised.
 128
 129MAPIO(func)
 130        Machine specific function to map IO areas (including the debug
 131        region above).
 132
 133INITIRQ(func)
 134        Machine specific function to initialise interrupts.
 135
 136
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