Kernel initialisation parameters on ARM Linux

The following document describes the kernel initialisation parameterstructure, otherwise known as ‘struct param_struct’ which is usedfor most ARM Linux architectures.

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

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

page_size
This parameter must be set to the page size of the machine, andwill be checked by the kernel.
nr_pages

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

If the system contains separate VRAM, this value should notinclude this information.

ramdisk_size
This is now obsolete, and should not be used.
flags

Various kernel flags, including:

bit 01 = mount root read only
bit 1unused
bit 20 = load ramdisk
bit 30 = 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 otherpurpose.

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

video_x / video_y
This describes the character position of cursor on VGA console, andis otherwise unused. (should not be used for other console types, andshould not be used for other purposes).
memc_control_reg
MEMC chip control register for Acorn Archimedes and Acorn A5000based machines. May be used differently by different architectures.
sounddefault
Default sound setting on Acorn machines. May be used differently bydifferent architectures.
adfsdrives
Number of ADFS/MFM disks. May be used differently by differentarchitectures.
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 memoryis non-contiguous from the processors point of view.
pages_in_vram
Number of pages in VRAM (used on Acorn RiscPC). This value may alsobe used by loaders if the size of the video RAM can’t be obtainedfrom the hardware.
initrd_start / initrd_size
This describes the kernel virtual start address and size of theinitial 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 between0-66 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.