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authorGrant Likely <grant.likely@secretlab.ca>2011-01-31 00:09:58 -0700
committerGrant Likely <grant.likely@secretlab.ca>2011-01-31 13:18:33 -0700
commit9830fcd6f6a4781d8b46d2b35c13b39f30915c63 (patch)
treea27be74182dc984678bcbb1668105adaf5a6efb0 /Documentation/devicetree/booting-without-of.txt
parentcf4e5c6e8d2b87ae8e61168a7dc860d68c578745 (diff)
downloadlinux-stericsson-9830fcd6f6a4781d8b46d2b35c13b39f30915c63.tar.gz
dt: add documentation of ARM dt boot interface
v3: added details to Documentation/arm/Booting Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Diffstat (limited to 'Documentation/devicetree/booting-without-of.txt')
-rw-r--r--Documentation/devicetree/booting-without-of.txt40
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diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
index 28b1c9d3d351..9381a1481027 100644
--- a/Documentation/devicetree/booting-without-of.txt
+++ b/Documentation/devicetree/booting-without-of.txt
@@ -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
========================