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 Signed-off-by: Grant Likely grant.likely@secretlab.ca --- Documentation/arm/Booting | 33 ++++++++++++++-- Documentation/devicetree/booting-without-of.txt | 48 +++++++++++++++++++++-- 2 files changed, 73 insertions(+), 8 deletions(-)
diff --git a/Documentation/arm/Booting b/Documentation/arm/Booting index 7685029..4e686a2 100644 --- a/Documentation/arm/Booting +++ b/Documentation/arm/Booting @@ -65,13 +65,19 @@ looks at the connected hardware is beyond the scope of this document. The boot loader must ultimately be able to provide a MACH_TYPE_xxx value to the kernel. (see linux/arch/arm/tools/mach-types).
- -4. Setup the kernel tagged list -------------------------------- +4. Setup boot data +------------------
Existing boot loaders: OPTIONAL, HIGHLY RECOMMENDED New boot loaders: MANDATORY
+The boot loader must provide either a tagged list or a dtb image for +passing configuration data to the kernel. The physical address of the +boot data is passed to the kernel in register r2. + +4a. Setup the kernel tagged list +-------------------------------- + The boot loader must create and initialise the kernel tagged list. A valid tagged list starts with ATAG_CORE and ends with ATAG_NONE. The ATAG_CORE tag may or may not be empty. An empty ATAG_CORE tag @@ -101,6 +107,24 @@ The tagged list must be placed in a region of memory where neither the kernel decompressor nor initrd 'bootp' program will overwrite it. The recommended placement is in the first 16KiB of RAM.
+4b. Setup the device tree +------------------------- + +The boot loader must load a device tree image (dtb) into system ram +at a 64bit aligned address and initialize it with the boot data. The +dtb format is documented in Documentation/devicetree/booting-without-of.txt. +The kernel will look for the dtb magic value of 0xd00dfeed at the dtb +physical address to determine if a dtb has been passed instead of a +tagged list. + +The boot loader must pass at a minimum the size and location of the +system memory, and the root filesystem location. The dtb must be +placed in a region of memory where the kernel decompressor will not +overwrite it. The recommended placement is in the first 16KiB of RAM +with the caveat that it may not be located at physical address 0 since +the kernel interprets a value of 0 in r2 to mean neither a tagged list +nor a dtb were passed. + 5. Calling the kernel image ---------------------------
@@ -125,7 +149,8 @@ In either case, the following conditions must be met: - CPU register settings r0 = 0, r1 = machine type number discovered in (3) above. - r2 = physical address of tagged list in system RAM. + r2 = physical address of tagged list in system RAM, or + physical address of device tree block (dtb) in system RAM
- CPU mode All forms of interrupts must be disabled (IRQs and FIQs) diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt index 50619a0..7c1329d 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,