* 3.11-rc7 big endian - atags and bootloader updates
[not found] <20130903104027.GB26613@localhost.localdomain>
@ 2013-09-03 16:15 ` Ben Dooks
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From: Ben Dooks @ 2013-09-03 16:15 UTC (permalink / raw)
To: linux-arm-kernel
On 03/09/13 11:40, Dave Martin wrote:
> On Fri, Aug 30, 2013 at 08:17:56PM +0100, Ben Dooks wrote:
>> This series is to better support older bootloaders, especially the
>> ones that still pass some information in the ATAGS structure used
>> by pre-fdt booting. The series is available at:
>>
>> git://git.baserock.org/delta/linux baserock/311-rc7/be/atags-v2
>
> This seems a good idea, but it is a change to the boot protocol which
> may break any existing BE bootloader today. Are you sure this won't
> cause problems for anyone?
You have to manually select it, so not really.
> One partial solution could be to make the ATAGs endianness-agnostic.
>
> Since the ATAGs start with ATAG core, we know that the word at offset
> <atags base + 4> must have the value 0x54410001. If we see a backwards
> value, we know the ATAGs are wrong-endian and every word must must be
> swabbed.
That would be possible, I will look into that.
> What to do about the zImage magic is less clear. Up to this point,
> BE kernels have always had backwards magic. Changing the magic might
> upset existing bootloaders, but I've never used a BE be bootloader, so
> I can't really comment on that...
This series uses a specific configuration to change both the ATAG
and magic if the system is meant to be big-endian, but booted on
a little-endian system.
>
> Documentation/arm/Booting should also be updated to reflect any change.
> In fact, what's already there could use clarification, since there is
> no statement about endianness at all yet.
Ok, good idea.
--
Ben Dooks http://www.codethink.co.uk/
Senior Engineer Codethink - Providing Genius
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