[PATCH] ARM: head: Remove boot-time HYP mode check for v5 and below

[Marko Katić]

On Mon, Dec 10, 2012 at 11:57 AM, Dave Martin <dave.martin at linaro.org> wrote:
> Hi Russell,
>
> Do you want me to send this patch to the patch system?
>
> Until we have confirmation from Marko (or someone else with a board)
> there's no way to know whether it fixes the problem.  But it should
> restore us back to the old behaviour older hardware, reducing the
> likelihood of side issues.
>
> This could be reverted later if it proves to be unnecessary.
>
> Cheers
> ---Dave
>
> On Fri, Dec 07, 2012 at 01:45:59PM +0000, Dave Martin wrote:
>> The kernel can only be entered on HYP mode on CPUs which actually
>> support it, i.e.  >= ARMv7.  pre-v6 platform support cannot coexist
>> in the same kernel as support for v7 and higher, so there is no
>> advantage in having the HYP mode check on pre-v6 hardware.
>>
>> At least one pre-v6 board is known to fail when the HYP mode check
>> code is present, although the exact cause remains unknown and may
>> be unrelated.  [1]
>>
>> This patch restores the old behaviour for pre-v6 platforms, whereby
>> the CPSR is forced directly to SVC mode with IRQs and FIQs masked.
>> All kernels capable of booting on v7 hardware will retain the
>> check, so this should not impair functionality.
>>
>> [1] http://lists.arm.linux.org.uk/lurker/message/20121130.013814.19218413.en.html
>> ([ARM] head.S change broke platform device registration?)
>>
>> Signed-off-by: Dave Martin <dave.martin at linaro.org>
>> ---
>>  arch/arm/include/asm/assembler.h |    8 ++++++++
>>  1 files changed, 8 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
>> index 2ef9581..eb87200 100644
>> --- a/arch/arm/include/asm/assembler.h
>> +++ b/arch/arm/include/asm/assembler.h
>> @@ -250,6 +250,7 @@
>>   * Beware, it also clobers LR.
>>   */
>>  .macro safe_svcmode_maskall reg:req
>> +#if __LINUX_ARM_ARCH__ >= 6
>>       mrs     \reg , cpsr
>>       mov     lr , \reg
>>       and     lr , lr , #MODE_MASK
>> @@ -266,6 +267,13 @@ THUMB(   orr     \reg , \reg , #PSR_T_BIT        )
>>       __ERET
>>  1:   msr     cpsr_c, \reg
>>  2:
>> +#else
>> +/*
>> + * workaround for possibly broken pre-v6 hardware
>> + * (akita, Sharp Zaurus C-1000, PXA270-based)
>> + */
>> +     setmode PSR_F_BIT | PSR_I_BIT | SVC_MODE, \reg
>> +#endif
>>  .endm
>>
>>  /*
>> --
>> 1.7.4.1
>>

I confirm that this patch fixes the regression on Akita machines
introduced with commit:

424e5994e63326a42012f003f1174f3c363c7b62
ARM: zImage/virt: hyp mode entry support for the zImage loader

The abovementioned commit breaks Zaurus machine ID detection code
(arm/boot/compressed/head-sharpsl.S)
causing Akita machines to boot with the wrong machine ID.

Just a minor nitpick:
s/clobers/clobbers/g