Documentation/arch/arm/booting.rst

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=================
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. Load initramfs.
6. 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/admin-guide/kernel-parameters.rst.


3. Detect the machine type
--------------------------

Existing boot loaders:
	OPTIONAL
New boot loaders:
	MANDATORY except for DT-only platforms

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