path: root/Documentation/devicetree/booting-without-of.txt
diff options
authorGrant Likely <grant.likely@secretlab.ca>2011-04-28 14:27:23 -0600
committerGrant Likely <grant.likely@secretlab.ca>2011-05-23 09:30:20 -0600
commitede338f4ce2fb5ee99d18751df32fbd3b10df268 (patch)
tree714bfcb440e54bae62d3a73f1de9d4b33ca69c21 /Documentation/devicetree/booting-without-of.txt
parent93c02ab40ae6e06cb24d14845d9f008fdd24f43d (diff)
dt: add documentation of ARM dt boot interface
v6: typo fixes v5: clarified that dtb should be aligned on a 64 bit boundary in RAM. v3: added details to Documentation/arm/Booting Acked-by: Tony Lindgren <tony@atomide.com> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org> Acked-by: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Diffstat (limited to 'Documentation/devicetree/booting-without-of.txt')
1 files changed, 44 insertions, 4 deletions
diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
index 50619a0720a8..7c1329de0596 100644
--- a/Documentation/devicetree/booting-without-of.txt
+++ b/Documentation/devicetree/booting-without-of.txt
@@ -12,8 +12,9 @@ Table of Contents
I - Introduction
- 1) Entry point for arch/powerpc
- 2) Entry point for arch/x86
+ 1) Entry point for arch/arm
+ 2) Entry point for arch/powerpc
+ 3) Entry point for arch/x86
II - The DT block format
1) Header
@@ -148,7 +149,46 @@ 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 r2 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
@@ -226,7 +266,7 @@ it with special cases.
cannot support both configurations with Book E and configurations
with classic Powerpc architectures.
-2) Entry point for arch/x86
+3) Entry point for arch/x86
There is one single 32bit entry point to the kernel at code32_start,