Revert "dt: add documentation of ARM dt boot interface"
This reverts commit 9830fcd6f6.
The ARM dt support has not been merged yet; this documentation update
was premature.
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
hifive-unleashed-5.1
Grant Likely
parent
9830fcd6f6
commit
7211da1778
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@ -65,19 +65,13 @@ looks at the connected hardware is beyond the scope of this document.
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The boot loader must ultimately be able to provide a MACH_TYPE_xxx
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value to the kernel. (see linux/arch/arm/tools/mach-types).
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4. Setup boot data
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------------------
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4. Setup the kernel tagged list
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-------------------------------
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Existing boot loaders: OPTIONAL, HIGHLY RECOMMENDED
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New boot loaders: MANDATORY
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The boot loader must provide either a tagged list or a dtb image for
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passing configuration data to the kernel. The physical address of the
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boot data is passed to the kernel in register r2.
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4a. Setup the kernel tagged list
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--------------------------------
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The boot loader must create and initialise the kernel tagged list.
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A valid tagged list starts with ATAG_CORE and ends with ATAG_NONE.
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The ATAG_CORE tag may or may not be empty. An empty ATAG_CORE tag
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@ -107,24 +101,6 @@ The tagged list must be placed in a region of memory where neither
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the kernel decompressor nor initrd 'bootp' program will overwrite
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it. The recommended placement is in the first 16KiB of RAM.
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4b. Setup the device tree
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-------------------------
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The boot loader must load a device tree image (dtb) into system ram
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at a 64bit aligned address and initialize it with the boot data. The
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dtb format is documented in Documentation/devicetree/booting-without-of.txt.
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The kernel will look for the dtb magic value of 0xd00dfeed at the dtb
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physical address to determine if a dtb has been passed instead of a
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tagged list.
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The boot loader must pass at a minimum the size and location of the
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system memory, and the root filesystem location. The dtb must be
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placed in a region of memory where the kernel decompressor will not
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overwrite it. The recommended placement is in the first 16KiB of RAM
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with the caveat that it may not be located at physical address 0 since
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the kernel interprets a value of 0 in r2 to mean neither a tagged list
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nor a dtb were passed.
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5. Calling the kernel image
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---------------------------
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@ -149,8 +125,7 @@ In either case, the following conditions must be met:
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- CPU register settings
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r0 = 0,
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r1 = machine type number discovered in (3) above.
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r2 = physical address of tagged list in system RAM, or
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physical address of device tree block (dtb) in system RAM
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r2 = physical address of tagged list in system RAM.
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- CPU mode
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All forms of interrupts must be disabled (IRQs and FIQs)
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@ -13,7 +13,6 @@ Table of Contents
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I - Introduction
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1) Entry point for arch/powerpc
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2) Entry point for arch/arm
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II - The DT block format
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1) Header
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@ -226,45 +225,6 @@ it with special cases.
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cannot support both configurations with Book E and configurations
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with classic Powerpc architectures.
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2) Entry point for arch/arm
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---------------------------
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There is one single entry point to the kernel, at the start
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of the kernel image. That entry point supports two calling
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conventions. A summary of the interface is described here. A full
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description of the boot requirements is documented in
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Documentation/arm/Booting
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a) ATAGS interface. Minimal information is passed from firmware
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to the kernel with a tagged list of predefined parameters.
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r0 : 0
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r1 : Machine type number
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r2 : Physical address of tagged list in system RAM
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b) Entry with a flattened device-tree block. Firmware loads the
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physical address of the flattened device tree block (dtb) into r2,
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r1 is not used, but it is considered good practise to use a valid
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machine number as described in Documentation/arm/Booting.
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r0 : 0
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r1 : Valid machine type number. When using a device tree,
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a single machine type number will often be assigned to
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represent a class or family of SoCs.
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r2 : physical pointer to the device-tree block
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(defined in chapter II) in RAM. Device tree can be located
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anywhere in system RAM, but it should be aligned on a 32 bit
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boundary.
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The kernel will differentiate between ATAGS and device tree booting by
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reading the memory pointed to by r1 and looking for either the flattened
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device tree block magic value (0xd00dfeed) or the ATAG_CORE value at
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offset 0x4 from r2 (0x54410001).
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II - The DT block format
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========================
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