Commit 83d26d11 authored by Ian Campbell's avatar Ian Campbell Committed by Russell King
Browse files

ARM: 7824/1: update advice on kernel, initramfs and FDT load address. 



  - Recommend that the kernel be placed under 128MiB, this is required if
    CONFIG_AUTO_ZRELADDR=y and good (or at least not bad) advice even if
    CONFIG_AUTO_ZRELADDR=n.
  - Recommend that a zImage kernel be placed above 32MiB, this avoids the need
    to relocate prior to decompression, which can speed up boot.
  - Add basic info on the requirements when loading a raw (non-zImage) kernel
    which are stricter than the zImage requirements.
  - Recommend that the DTB be placed after the 128MiB boundary, avoiding any
    potential conflict with the kernel decompressor, and within the lowmem
    region.  In practice it could follow the kernel loaded after 32MiB,
    assuming the kernel decompesses to less than 32MiB, but the 128MiB
    recommendation is simple and unambiguous.
  - Add similar recommendation regarding initramfs.

Signed-off-by: default avatarIan Campbell <ian.campbell@citrix.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Dave Martin <dave.martin@linaro.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Roy Franz <roy.franz@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 09096f6a

Documentation/arm/Booting

+32 −10
Original line number Diff line number Diff line
@@ -18,7 +18,8 @@ following: 
2. Initialise one serial port.

3. Detect the machine type.

4. Setup the kernel tagged list.

5. Call the kernel image.

5. Load initramfs.

6. Call the kernel image.





1. Setup and initialise RAM
@@ -120,12 +121,27 @@ 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.

overwrite it, whilst remaining within the region which will be covered

by the kernel's low-memory mapping.



5. Calling the kernel image

A safe location is just above the 128MiB boundary from start of RAM.



5. Load initramfs.

------------------



Existing boot loaders:		OPTIONAL

New boot loaders:		OPTIONAL



If an initramfs is in use then, as with the dtb, it must be placed in

a region of memory where the kernel decompressor will not overwrite it

while also with the region which will be covered by the kernel's

low-memory mapping.



A safe location is just above the device tree blob which itself will

be loaded just above the 128MiB boundary from the start of RAM as

recommended above.



6. Calling the kernel image

---------------------------



Existing boot loaders:		MANDATORY
@@ -136,11 +152,17 @@ is stored in flash, and is linked correctly to be run from flash, 
then it is legal for the boot loader to call the zImage in flash

directly.



The zImage may also be placed in system RAM (at any location) and

called there.  Note that the kernel uses 16K of RAM below the image

to store page tables.  The recommended placement is 32KiB into RAM.

The zImage may also be placed in system RAM and called there.  The

kernel should be placed in the first 128MiB of RAM.  It is recommended

that it is loaded above 32MiB in order to avoid the need to relocate

prior to decompression, which will make the boot process slightly

faster.



When booting a raw (non-zImage) kernel the constraints are tighter.

In this case the kernel must be loaded at an offset into system equal

to TEXT_OFFSET - PAGE_OFFSET.



In either case, the following conditions must be met:

In any case, the following conditions must be met:



- Quiesce all DMA capable devices so that memory does not get

  corrupted by bogus network packets or disk data. This will save

CRA Git | Maintained and supported by SUSTech CRA and CCSE