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MIPS: BMIPS: Document the firmware->kernel DTB interface

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Add a new section covering the Generic BMIPS machine type.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: f.fainelli@gmail.com
Cc: jaedon.shin@gmail.com
Cc: abrestic@chromium.org
Cc: tglx@linutronix.de
Cc: jason@lakedaemon.net
Cc: jogo@openwrt.org
Cc: arnd@arndb.de
Cc: computersforpeace@gmail.com
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/8849/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Kevin Cernekee 2014-12-25 09:49:11 -08:00 committed by Ralf Baechle
parent 5432eeb6fa
commit 9c24ce29b2
1 changed files with 28 additions and 0 deletions
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28
Documentation/devicetree/booting-without-of.txt
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@ -15,6 +15,7 @@ Table of Contents
1) Entry point for arch/arm
2) Entry point for arch/powerpc
3) Entry point for arch/x86
4) Entry point for arch/mips/bmips
II - The DT block format
1) Header
@ -288,6 +289,33 @@ it with special cases.
or initrd address. It simply holds information which can not be retrieved
otherwise like interrupt routing or a list of devices behind an I2C bus.
4) Entry point for arch/mips/bmips
----------------------------------
Some bootloaders only support a single entry point, at the start of the
kernel image. Other bootloaders will jump to the ELF start address.
Both schemes are supported; CONFIG_BOOT_RAW=y and CONFIG_NO_EXCEPT_FILL=y,
so the first instruction immediately jumps to kernel_entry().
Similar to the arch/arm case (b), a DT-aware bootloader is expected to
set up the following registers:
a0 : 0
a1 : 0xffffffff
a2 : Physical pointer to the device tree block (defined in chapter
II) in RAM. The device tree can be located anywhere in the first
512MB of the physical address space (0x00000000 - 0x1fffffff),
aligned on a 64 bit boundary.
Legacy bootloaders do not use this convention, and they do not pass in a
DT block. In this case, Linux will look for a builtin DTB, selected via
CONFIG_DT_*.
This convention is defined for 32-bit systems only, as there are not
currently any 64-bit BMIPS implementations.
II - The DT block format
========================