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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 1) Entry point for arch/arm
2) Entry point for arch/powerpc 2) Entry point for arch/powerpc
3) Entry point for arch/x86 3) Entry point for arch/x86
4) Entry point for arch/mips/bmips
II - The DT block format II - The DT block format
1) Header 1) Header
@ -288,6 +289,33 @@ it with special cases.
or initrd address. It simply holds information which can not be retrieved 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. 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 II - The DT block format
======================== ========================