Documentation/arm/setup.rst

   1 =============================================
   2 Kernel initialisation parameters on ARM Linux
   3 =============================================
   4
   5 The following document describes the kernel initialisation parameter
   6 structure, otherwise known as 'struct param_struct' which is used
   7 for most ARM Linux architectures.
   8
   9 This structure is used to pass initialisation parameters from the
  10 kernel loader to the Linux kernel proper, and may be short lived
  11 through the kernel initialisation process.  As a general rule, it
  12 should not be referenced outside of arch/arm/kernel/setup.c:setup_arch().
  13
  14 There are a lot of parameters listed in there, and they are described
  15 below:
  16
  17  page_size
  18    This parameter must be set to the page size of the machine, and
  19    will be checked by the kernel.
  20
  21  nr_pages
  22    This is the total number of pages of memory in the system.  If
  23    the memory is banked, then this should contain the total number
  24    of pages in the system.
  25
  26    If the system contains separate VRAM, this value should not
  27    include this information.
  28
  29  ramdisk_size
  30    This is now obsolete, and should not be used.
  31
  32  flags
  33    Various kernel flags, including:
  34
  35     =====   ========================
  36     bit 0   1 = mount root read only
  37     bit 1   unused
  38     bit 2   0 = load ramdisk
  39     bit 3   0 = prompt for ramdisk
  40     =====   ========================
  41
  42  rootdev
  43    major/minor number pair of device to mount as the root filesystem.
  44
  45  video_num_cols / video_num_rows
  46    These two together describe the character size of the dummy console,
  47    or VGA console character size.  They should not be used for any other
  48    purpose.
  49
  50    It's generally a good idea to set these to be either standard VGA, or
  51    the equivalent character size of your fbcon display.  This then allows
  52    all the bootup messages to be displayed correctly.
  53
  54  video_x / video_y
  55    This describes the character position of cursor on VGA console, and
  56    is otherwise unused. (should not be used for other console types, and
  57    should not be used for other purposes).
  58
  59  memc_control_reg
  60    MEMC chip control register for Acorn Archimedes and Acorn A5000
  61    based machines.  May be used differently by different architectures.
  62
  63  sounddefault
  64    Default sound setting on Acorn machines.  May be used differently by
  65    different architectures.
  66
  67  adfsdrives
  68    Number of ADFS/MFM disks.  May be used differently by different
  69    architectures.
  70
  71  bytes_per_char_h / bytes_per_char_v
  72    These are now obsolete, and should not be used.
  73
  74  pages_in_bank[4]
  75    Number of pages in each bank of the systems memory (used for RiscPC).
  76    This is intended to be used on systems where the physical memory
  77    is non-contiguous from the processors point of view.
  78
  79  pages_in_vram
  80    Number of pages in VRAM (used on Acorn RiscPC).  This value may also
  81    be used by loaders if the size of the video RAM can't be obtained
  82    from the hardware.
  83
  84  initrd_start / initrd_size
  85    This describes the kernel virtual start address and size of the
  86    initial ramdisk.
  87
  88  rd_start
  89    Start address in sectors of the ramdisk image on a floppy disk.
  90
  91  system_rev
  92    system revision number.
  93
  94  system_serial_low / system_serial_high
  95    system 64-bit serial number
  96
  97  mem_fclk_21285
  98    The speed of the external oscillator to the 21285 (footbridge),
  99    which control's the speed of the memory bus, timer & serial port.
 100    Depending upon the speed of the cpu its value can be between
 101    0-66 MHz. If no params are passed or a value of zero is passed,
 102    then a value of 50 Mhz is the default on 21285 architectures.
 103
 104  paths[8][128]
 105    These are now obsolete, and should not be used.
 106
 107  commandline
 108    Kernel command line parameters.  Details can be found elsewhere.