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| author | Grant Likely <grant.likely@secretlab.ca> | 2011-04-28 22:27:23 +0200 |
|---|---|---|
| committer | Grant Likely <grant.likely@secretlab.ca> | 2011-05-23 17:30:20 +0200 |
| commit | ede338f4ce2fb5ee99d18751df32fbd3b10df268 (patch) | |
| tree | 714bfcb440e54bae62d3a73f1de9d4b33ca69c21 /Documentation/devicetree/booting-without-of.txt | |
| parent | arm/dt: probe for platforms via the device tree (diff) | |
| download | linux-ede338f4ce2fb5ee99d18751df32fbd3b10df268.tar.xz linux-ede338f4ce2fb5ee99d18751df32fbd3b10df268.zip | |
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')
| -rw-r--r-- | Documentation/devicetree/booting-without-of.txt | 48 |
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, |