setup.rst

  1=============================================
  2Kernel initialisation parameters on ARM Linux
  3=============================================
  4
  5The following document describes the kernel initialisation parameter
  6structure, otherwise known as 'struct param_struct' which is used
  7for most ARM Linux architectures.
  8
  9This structure is used to pass initialisation parameters from the
 10kernel loader to the Linux kernel proper, and may be short lived
 11through the kernel initialisation process.  As a general rule, it
 12should not be referenced outside of arch/arm/kernel/setup.c:setup_arch().
 13
 14There are a lot of parameters listed in there, and they are described
 15below:
 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.