xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

dt: add documentation of ARM dt boot interface

Browse Source 
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>
This commit is contained in:
Grant Likely
2011-04-28 14:27:23 -06:00
parent 93c02ab40a
commit ede338f4ce
2 changed files with 73 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

33
Documentation/arm/Booting
View File

@@ -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)