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dt: add documentation of ARM dt boot interface

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v3: added details to Documentation/arm/Booting

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
This commit is contained in:
Grant Likely 2011-01-31 00:09:58 -07:00
parent cf4e5c6e8d
commit 9830fcd6f6
2 changed files with 69 additions and 4 deletions
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40
Documentation/devicetree/booting-without-of.txt
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@ -13,6 +13,7 @@ Table of Contents
I - Introduction
1) Entry point for arch/powerpc
2) Entry point for arch/arm
II - The DT block format
1) Header
@ -225,6 +226,45 @@ it with special cases.
cannot support both configurations with Book E and configurations
with classic Powerpc architectures.
2) Entry point for arch/arm
---------------------------
There is one single entry point to the kernel, at the start
of the kernel image. That entry point supports two calling
conventions. A summary of the interface is described here. A full
description of the boot requirements is documented in
Documentation/arm/Booting
a) ATAGS interface. Minimal information is passed from firmware
to the kernel with a tagged list of predefined parameters.
r0 : 0
r1 : Machine type number
r2 : Physical address of tagged list in system RAM
b) Entry with a flattened device-tree block. Firmware loads the
physical address of the flattened device tree block (dtb) into r2,
r1 is not used, but it is considered good practise to use a valid
machine number as described in Documentation/arm/Booting.
r0 : 0
r1 : Valid machine type number. When using a device tree,
a single machine type number will often be assigned to
represent a class or family of SoCs.
r2 : physical pointer to the device-tree block
(defined in chapter II) in RAM. Device tree can be located
anywhere in system RAM, but it should be aligned on a 32 bit
boundary.
The kernel will differentiate between ATAGS and device tree booting by
reading the memory pointed to by r1 and looking for either the flattened
device tree block magic value (0xd00dfeed) or the ATAG_CORE value at
offset 0x4 from r2 (0x54410001).
II - The DT block format
========================