[mirror_ubuntu-bionic-kernel.git] / Documentation / arm / Setup

Kernel initialisation parameters on ARM Linux
---------------------------------------------

The following document describes the kernel initialisation parameter
structure, otherwise known as 'struct param_struct' which is used
for most ARM Linux architectures.

This structure is used to pass initialisation parameters from the
kernel loader to the Linux kernel proper, and may be short lived
through the kernel initialisation process.  As a general rule, it
should not be referenced outside of arch/arm/kernel/setup.c:setup_arch().

There are a lot of parameters listed in there, and they are described
below:

 page_size

   This parameter must be set to the page size of the machine, and
   will be checked by the kernel.

 nr_pages

   This is the total number of pages of memory in the system.  If
   the memory is banked, then this should contain the total number
   of pages in the system.

   If the system contains separate VRAM, this value should not
   include this information.

 ramdisk_size

   This is now obsolete, and should not be used.

 flags

   Various kernel flags, including:
    bit 0 - 1 = mount root read only
    bit 1 - unused
    bit 2 - 0 = load ramdisk
    bit 3 - 0 = prompt for ramdisk

 rootdev

   major/minor number pair of device to mount as the root filesystem.

 video_num_cols
 video_num_rows

   These two together describe the character size of the dummy console,
   or VGA console character size.  They should not be used for any other
   purpose.

   It's generally a good idea to set these to be either standard VGA, or
   the equivalent character size of your fbcon display.  This then allows
   all the bootup messages to be displayed correctly.

 video_x
 video_y

   This describes the character position of cursor on VGA console, and
   is otherwise unused. (should not be used for other console types, and
   should not be used for other purposes).

 memc_control_reg

   MEMC chip control register for Acorn Archimedes and Acorn A5000
   based machines.  May be used differently by different architectures.

 sounddefault

   Default sound setting on Acorn machines.  May be used differently by
   different architectures.

 adfsdrives

   Number of ADFS/MFM disks.  May be used differently by different
   architectures.

 bytes_per_char_h
 bytes_per_char_v

   These are now obsolete, and should not be used.

 pages_in_bank[4]

   Number of pages in each bank of the systems memory (used for RiscPC).
   This is intended to be used on systems where the physical memory
   is non-contiguous from the processors point of view.

 pages_in_vram

   Number of pages in VRAM (used on Acorn RiscPC).  This value may also
   be used by loaders if the size of the video RAM can't be obtained
   from the hardware.

 initrd_start
 initrd_size

   This describes the kernel virtual start address and size of the
   initial ramdisk.

 rd_start

   Start address in sectors of the ramdisk image on a floppy disk.

 system_rev

   system revision number.

 system_serial_low
 system_serial_high

   system 64-bit serial number

 mem_fclk_21285

   The speed of the external oscillator to the 21285 (footbridge),
   which control's the speed of the memory bus, timer & serial port.
   Depending upon the speed of the cpu its value can be between
   0-66 MHz. If no params are passed or a value of zero is passed,
   then a value of 50 Mhz is the default on 21285 architectures.

 paths[8][128]

   These are now obsolete, and should not be used.

 commandline

   Kernel command line parameters.  Details can be found elsewhere.
Commit	Line	Data
1da177e4 LT	1	Kernel initialisation parameters on ARM Linux
	2	---------------------------------------------
	3
	4	The following document describes the kernel initialisation parameter
	5	structure, otherwise known as 'struct param_struct' which is used
	6	for most ARM Linux architectures.
	7
	8	This structure is used to pass initialisation parameters from the
	9	kernel loader to the Linux kernel proper, and may be short lived
	10	through the kernel initialisation process. As a general rule, it
	11	should not be referenced outside of arch/arm/kernel/setup.c:setup_arch().
	12
	13	There are a lot of parameters listed in there, and they are described
	14	below:
	15
	16	page_size
	17
	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
	23	This is the total number of pages of memory in the system. If
	24	the memory is banked, then this should contain the total number
	25	of pages in the system.
	26
	27	If the system contains separate VRAM, this value should not
	28	include this information.
	29
	30	ramdisk_size
	31
	32	This is now obsolete, and should not be used.
	33
	34	flags
	35
	36	Various kernel flags, including:
	37	bit 0 - 1 = mount root read only
	38	bit 1 - unused
	39	bit 2 - 0 = load ramdisk
	40	bit 3 - 0 = prompt for ramdisk
	41
	42	rootdev
	43
	44	major/minor number pair of device to mount as the root filesystem.
	45
	46	video_num_cols
	47	video_num_rows
	48
	49	These two together describe the character size of the dummy console,
	50	or VGA console character size. They should not be used for any other
	51	purpose.
	52
	53	It's generally a good idea to set these to be either standard VGA, or
	54	the equivalent character size of your fbcon display. This then allows
	55	all the bootup messages to be displayed correctly.
	56
	57	video_x
	58	video_y
	59
	60	This describes the character position of cursor on VGA console, and
13fce806	61	is otherwise unused. (should not be used for other console types, and
1da177e4 LT	62	should not be used for other purposes).
	63
	64	memc_control_reg
	65
	66	MEMC chip control register for Acorn Archimedes and Acorn A5000
	67	based machines. May be used differently by different architectures.
	68
	69	sounddefault
	70
	71	Default sound setting on Acorn machines. May be used differently by
	72	different architectures.
	73
	74	adfsdrives
	75
	76	Number of ADFS/MFM disks. May be used differently by different
	77	architectures.
	78
	79	bytes_per_char_h
	80	bytes_per_char_v
	81
	82	These are now obsolete, and should not be used.
	83
	84	pages_in_bank[4]
	85
	86	Number of pages in each bank of the systems memory (used for RiscPC).
	87	This is intended to be used on systems where the physical memory
	88	is non-contiguous from the processors point of view.
	89
	90	pages_in_vram
	91
	92	Number of pages in VRAM (used on Acorn RiscPC). This value may also
	93	be used by loaders if the size of the video RAM can't be obtained
	94	from the hardware.
	95
	96	initrd_start
	97	initrd_size
	98
	99	This describes the kernel virtual start address and size of the
	100	initial ramdisk.
	101
	102	rd_start
	103
	104	Start address in sectors of the ramdisk image on a floppy disk.
	105
	106	system_rev
	107
	108	system revision number.
	109
	110	system_serial_low
	111	system_serial_high
	112
	113	system 64-bit serial number
	114
	115	mem_fclk_21285
	116
	117	The speed of the external oscillator to the 21285 (footbridge),
	118	which control's the speed of the memory bus, timer & serial port.
	119	Depending upon the speed of the cpu its value can be between
	120	0-66 MHz. If no params are passed or a value of zero is passed,
	121	then a value of 50 Mhz is the default on 21285 architectures.
	122
	123	paths[8][128]
	124
	125	These are now obsolete, and should not be used.
126
127	commandline
128
129	Kernel command line parameters. Details can be found elsewhere.