path: root/Documentation/devicetree/booting-without-of.txt
diff options
authorGrant Likely <grant.likely@secretlab.ca>2011-03-28 21:46:37 -0600
committerGrant Likely <grant.likely@secretlab.ca>2011-03-28 22:00:23 -0600
commit79af0e1433c7f02ea298fba67d5ffb6ac5b079d2 (patch)
tree7aa371f28ecac9fbcfe22f1bac78a7a6393b6ba5 /Documentation/devicetree/booting-without-of.txt
parent54a3318612a86f3a79cdfc37e8ab921ca39f6d85 (diff)
dt: add documentation of ARM dt boot interface
v5: clarified that dtb should be aligned on a 64 bit boundary in RAM. 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')
1 files changed, 42 insertions, 2 deletions
diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
index 28b1c9d3d35..a4d501963b7 100644
--- a/Documentation/devicetree/booting-without-of.txt
+++ b/Documentation/devicetree/booting-without-of.txt
@@ -12,7 +12,8 @@ Table of Contents
I - Introduction
- 1) Entry point for arch/powerpc
+ 1) Entry point for arch/arm
+ 2) Entry point for arch/powerpc
II - The DT block format
1) Header
@@ -147,7 +148,46 @@ upgrades without significantly impacting the kernel code or cluttering
it with special cases.
-1) Entry point for arch/powerpc
+1) 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 64 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).
+2) Entry point for arch/powerpc
There is one single entry point to the kernel, at the start