porting.rst (4514B)
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.