kernel decompressor problem for ARMv7

[Lin Ming]

On Tue, Jul 9, 2013 at 3:39 PM, Nicolas Pitre <nicolas.pitre at linaro.org> wrote:
> On Tue, 9 Jul 2013, Lin Ming wrote:
>
>> On Mon, Jul 8, 2013 at 10:27 AM, Lin Ming <minggr at gmail.com> wrote:
>> > On Sat, 2013-07-06 at 00:58 +0800, Lin Ming wrote:
>> >> On Sat, Jul 6, 2013 at 12:30 AM, Nicolas Pitre <nicolas.pitre at linaro.org> wrote:
>> >> > On Fri, 5 Jul 2013, Will Deacon wrote:
>> >> >
>> >> >> On Fri, Jul 05, 2013 at 09:44:12AM +0100, Lin Ming wrote:
>> >> >> > Hi all,
>> >> >>
>> >> >> Hello,
>> >> >>
>> >> >> > I'm porting BSP code from v2.6.36 to v3.10 kernel. It's ARMv7 processor.
>> >> >>
>> >> >> Which specific processor/SoC?
>> >> >>
>> >> >> > But decompressor doesn't work. With a lot of debug, I finally find
>> >> >> > below 2 commits related.
>> >> >> > Kernel uncompress OK with these commits reverted.
>> >> >> >
>> >> >> > dbece45: ARM: 7501/1: decompressor: reset ttbcr for VMSA ARMv7 cores
>> >> >> > (Introduced in v3.6-rc6)
>> >> >> >
>> >> >> > 5010192: ARM: 7583/1: decompressor: Enable unaligned memory access for
>> >> >> > v6 and above
>> >> >> > (Introduced in v3.7-rc8)
>> >> >> >
>> >> >> > Any hint to fix it?
>> >> >>
>> >> >> There's not really enough information to go on here. What specifically
>> >> >> fails? Also, do you have to revert *both* of the above changes to get things
>> >> >> working again?
>> >> >
>> >> > Also, what is the bootloader used here?
>> >>
>> >> uboot.
>> >>
>> >> >
>> >> > Does the bootloader call the kernel with the MMU off as documented in
>> >> > Documentation/arm/Booting?
>> >>
>> >> How to check this?
>> >>
>> >> I'll check uboot code or add debug code in boot/compressed/head.S to
>> >> check it next Monday.
>> >
>> > I added below debug code to print the control reg from lowest 4bits to
>> > highest 4bits.
>> >
>> > It prints "B7805C". So the control reg is 0x00c5087b.
>> > Seems bootloader calls the kernel with MMU enabled and Alignment fault
>> > checking enabled.
>>
>> Hi Nicolas,
>>
>> Is this information useful?
>> Or any other information needed for further debug?
>
> No more info needed.  The kernel has to be booted with the MMU disabled
> as per the booting protocol documentation. You therefore have to fix
> your
> bootloader.

OK.

But I have to also revert below commit to make decompressor work.

commit 5010192:
ARM: 7583/1: decompressor: Enable unaligned memory access for v6 and above

It seems like caused by bootloader has Alignment fault checking enabled.
Any suggestion how to fix it?

Thanks.

>
>
> Nicolas