mirror of
https://github.com/genesi/linux-legacy.git
synced 2026-07-08 17:56:55 +00:00
bce56e48c2
This bases on work done earlier by Lennert Buytenhek and Mark A. Greer. Compared to their approach zreladdr isn't guessed based on the pc register but the bootloader is expected to pass PHYS_OFFSET in r3. If that value doesn't look right (e.g. isn't aligned) it is guessed based on the value of sp. This should work for CONFIG_ZBOOT_ROM, too. To use it for your machine removing the definition of PHYS_OFFSET from <mach/memory.h> and selecting CONFIG_RUNTIME_PHYS_OFFSET should be enough. Cc: Lennert Buytenhek <buytenh@wantstofly.org> Cc: Steve Chen <schen@mvista.com> Cc: Mark A. Greer <mgreer@mvista.com> Cc: Kevin Hilman <khilman@deeprootsystems.com> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
143 lines
4.6 KiB
Plaintext
143 lines
4.6 KiB
Plaintext
Booting ARM Linux
|
|
=================
|
|
|
|
Author: Russell King
|
|
Date : 18 May 2002
|
|
|
|
The following documentation is relevant to 2.4.18-rmk6 and beyond.
|
|
|
|
In order to boot ARM Linux, you require a boot loader, which is a small
|
|
program that runs before the main kernel. The boot loader is expected
|
|
to initialise various devices, and eventually call the Linux kernel,
|
|
passing information to the kernel.
|
|
|
|
Essentially, the boot loader should provide (as a minimum) the
|
|
following:
|
|
|
|
1. Setup and initialise the RAM.
|
|
2. Initialise one serial port.
|
|
3. Detect the machine type.
|
|
4. Setup the kernel tagged list.
|
|
5. Call the kernel image.
|
|
|
|
|
|
1. Setup and initialise RAM
|
|
---------------------------
|
|
|
|
Existing boot loaders: MANDATORY
|
|
New boot loaders: MANDATORY
|
|
|
|
The boot loader is expected to find and initialise all RAM that the
|
|
kernel will use for volatile data storage in the system. It performs
|
|
this in a machine dependent manner. (It may use internal algorithms
|
|
to automatically locate and size all RAM, or it may use knowledge of
|
|
the RAM in the machine, or any other method the boot loader designer
|
|
sees fit.)
|
|
|
|
|
|
2. Initialise one serial port
|
|
-----------------------------
|
|
|
|
Existing boot loaders: OPTIONAL, RECOMMENDED
|
|
New boot loaders: OPTIONAL, RECOMMENDED
|
|
|
|
The boot loader should initialise and enable one serial port on the
|
|
target. This allows the kernel serial driver to automatically detect
|
|
which serial port it should use for the kernel console (generally
|
|
used for debugging purposes, or communication with the target.)
|
|
|
|
As an alternative, the boot loader can pass the relevant 'console='
|
|
option to the kernel via the tagged lists specifying the port, and
|
|
serial format options as described in
|
|
|
|
Documentation/kernel-parameters.txt.
|
|
|
|
|
|
3. Detect the machine type
|
|
--------------------------
|
|
|
|
Existing boot loaders: OPTIONAL
|
|
New boot loaders: MANDATORY
|
|
|
|
The boot loader should detect the machine type its running on by some
|
|
method. Whether this is a hard coded value or some algorithm that
|
|
looks at the connected hardware is beyond the scope of this document.
|
|
The boot loader must ultimately be able to provide a MACH_TYPE_xxx
|
|
value to the kernel. (see linux/arch/arm/tools/mach-types).
|
|
|
|
|
|
4. Setup the kernel tagged list
|
|
-------------------------------
|
|
|
|
Existing boot loaders: OPTIONAL, HIGHLY RECOMMENDED
|
|
New boot loaders: MANDATORY
|
|
|
|
The boot loader must create and initialise the kernel tagged list.
|
|
A valid tagged list starts with ATAG_CORE and ends with ATAG_NONE.
|
|
The ATAG_CORE tag may or may not be empty. An empty ATAG_CORE tag
|
|
has the size field set to '2' (0x00000002). The ATAG_NONE must set
|
|
the size field to zero.
|
|
|
|
Any number of tags can be placed in the list. It is undefined
|
|
whether a repeated tag appends to the information carried by the
|
|
previous tag, or whether it replaces the information in its
|
|
entirety; some tags behave as the former, others the latter.
|
|
|
|
The boot loader must pass at a minimum the size and location of
|
|
the system memory, and root filesystem location. Therefore, the
|
|
minimum tagged list should look:
|
|
|
|
+-----------+
|
|
base -> | ATAG_CORE | |
|
|
+-----------+ |
|
|
| ATAG_MEM | | increasing address
|
|
+-----------+ |
|
|
| ATAG_NONE | |
|
|
+-----------+ v
|
|
|
|
The tagged list should be stored in system RAM.
|
|
|
|
The tagged list must be placed in a region of memory where neither
|
|
the kernel decompressor nor initrd 'bootp' program will overwrite
|
|
it. The recommended placement is in the first 16KiB of RAM.
|
|
|
|
5. Calling the kernel image
|
|
---------------------------
|
|
|
|
Existing boot loaders: MANDATORY
|
|
New boot loaders: MANDATORY
|
|
|
|
There are two options for calling the kernel zImage. If the zImage
|
|
is stored in flash, and is linked correctly to be run from flash,
|
|
then it is legal for the boot loader to call the zImage in flash
|
|
directly.
|
|
|
|
The zImage may also be placed in system RAM (at any location) and
|
|
called there. Note that the kernel uses 16K of RAM below the image
|
|
to store page tables. The recommended placement is 32KiB into RAM.
|
|
|
|
In either case, the following conditions must be met:
|
|
|
|
- Quiesce all DMA capable devices so that memory does not get
|
|
corrupted by bogus network packets or disk data. This will save
|
|
you many hours of debug.
|
|
|
|
- CPU register settings
|
|
r0 = 0,
|
|
r1 = machine type number discovered in (3) above.
|
|
r2 = physical address of tagged list in system RAM.
|
|
r3 = PHYS_OFFSET
|
|
|
|
- CPU mode
|
|
All forms of interrupts must be disabled (IRQs and FIQs)
|
|
The CPU must be in SVC mode. (A special exception exists for Angel)
|
|
|
|
- Caches, MMUs
|
|
The MMU must be off.
|
|
Instruction cache may be on or off.
|
|
Data cache must be off.
|
|
|
|
- The boot loader is expected to call the kernel image by jumping
|
|
directly to the first instruction of the kernel image.
|
|
|