LXR linux/Documentation/arm/porting.rst

   1=======
   2Porting
   3=======
   4
   5Taken from list archive at http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2001-July/004064.html
   6
   7Initial definitions
   8-------------------
   9
  10The following symbol definitions rely on you knowing the translation that
  11__virt_to_phys() does for your machine.  This macro converts the passed
  12virtual address to a physical address.  Normally, it is simply:
  13
  14                phys = virt - PAGE_OFFSET + PHYS_OFFSET
  15
  16
  17Decompressor Symbols
  18--------------------
  19
  20ZTEXTADDR
  21        Start address of decompressor.  There's no point in talking about
  22        virtual or physical addresses here, since the MMU will be off at
  23        the time when you call the decompressor code.  You normally call
  24        the kernel at this address to start it booting.  This doesn't have
  25        to be located in RAM, it can be in flash or other read-only or
  26        read-write addressable medium.
  27
  28ZBSSADDR
  29        Start address of zero-initialised work area for the decompressor.
  30        This must be pointing at RAM.  The decompressor will zero initialise
  31        this for you.  Again, the MMU will be off.
  32
  33ZRELADDR
  34        This is the address where the decompressed kernel will be written,
  35        and eventually executed.  The following constraint must be valid:
  36
  37                __virt_to_phys(TEXTADDR) == ZRELADDR
  38
  39        The initial part of the kernel is carefully coded to be position
  40        independent.
  41
  42INITRD_PHYS
  43        Physical address to place the initial RAM disk.  Only relevant if
  44        you are using the bootpImage stuff (which only works on the old
  45        struct param_struct).
  46
  47INITRD_VIRT
  48        Virtual address of the initial RAM disk.  The following  constraint
  49        must be valid:
  50
  51                __virt_to_phys(INITRD_VIRT) == INITRD_PHYS
  52
  53PARAMS_PHYS
  54        Physical address of the struct param_struct or tag list, giving the
  55        kernel various parameters about its execution environment.
  56
  57
  58Kernel Symbols
  59--------------
  60
  61PHYS_OFFSET
  62        Physical start address of the first bank of RAM.
  63
  64PAGE_OFFSET
  65        Virtual start address of the first bank of RAM.  During the kernel
  66        boot phase, virtual address PAGE_OFFSET will be mapped to physical
  67        address PHYS_OFFSET, along with any other mappings you supply.
  68        This should be the same value as TASK_SIZE.
  69
  70TASK_SIZE
  71        The maximum size of a user process in bytes.  Since user space
  72        always starts at zero, this is the maximum address that a user
  73        process can access+1.  The user space stack grows down from this
  74        address.
  75
  76        Any virtual address below TASK_SIZE is deemed to be user process
  77        area, and therefore managed dynamically on a process by process
  78        basis by the kernel.  I'll call this the user segment.
  79
  80        Anything above TASK_SIZE is common to all processes.  I'll call
  81        this the kernel segment.
  82
  83        (In other words, you can't put IO mappings below TASK_SIZE, and
  84        hence PAGE_OFFSET).
  85
  86TEXTADDR
  87        Virtual start address of kernel, normally PAGE_OFFSET + 0x8000.
  88        This is where the kernel image ends up.  With the latest kernels,
  89        it must be located at 32768 bytes into a 128MB region.  Previous
  90        kernels placed a restriction of 256MB here.
  91
  92DATAADDR
  93        Virtual address for the kernel data segment.  Must not be defined
  94        when using the decompressor.
  95
  96VMALLOC_START / VMALLOC_END
  97        Virtual addresses bounding the vmalloc() area.  There must not be
  98        any static mappings in this area; vmalloc will overwrite them.
  99        The addresses must also be in the kernel segment (see above).
 100        Normally, the vmalloc() area starts VMALLOC_OFFSET bytes above the
 101        last virtual RAM address (found using variable high_memory).
 102
 103VMALLOC_OFFSET
 104        Offset normally incorporated into VMALLOC_START to provide a hole
 105        between virtual RAM and the vmalloc area.  We do this to allow
 106        out of bounds memory accesses (eg, something writing off the end
 107        of the mapped memory map) to be caught.  Normally set to 8MB.
 108
 109Architecture Specific Macros
 110----------------------------
 111
 112BOOT_MEM(pram,pio,vio)
 113        `pram` specifies the physical start address of RAM.  Must always
 114        be present, and should be the same as PHYS_OFFSET.
 115
 116        `pio` is the physical address of an 8MB region containing IO for
 117        use with the debugging macros in arch/arm/kernel/debug-armv.S.
 118
 119        `vio` is the virtual address of the 8MB debugging region.
 120
 121        It is expected that the debugging region will be re-initialised
 122        by the architecture specific code later in the code (via the
 123        MAPIO function).
 124
 125BOOT_PARAMS
 126        Same as, and see PARAMS_PHYS.
 127
 128FIXUP(func)
 129        Machine specific fixups, run before memory subsystems have been
 130        initialised.
 131
 132MAPIO(func)
 133        Machine specific function to map IO areas (including the debug
 134        region above).
 135
 136INITIRQ(func)
 137        Machine specific function to initialise interrupts.
 138