[U-Boot] [PATCH 1/2] arm: Replace v7_maint_dcache_all(ARMV7_DCACHE_CLEAN_INVAL_ALL) with asm code

[Hans de Goede]

Hi,

On 06-04-16 16:51, Tom Rini wrote:
> On Mon, Apr 04, 2016 at 08:31:48PM +0200, Hans de Goede wrote:
>
>> v7_maint_dcache_all() does not work reliable when build with gcc6,
>> see: https://bugzilla.redhat.com/show_bug.cgi?id=1318788
>>
>> While debugging this I learned that v7_maint_dcache_all() is unreliable
>> when build with gcc5 too when it is marked as noinline.
>>
>> This commit fixes the reliability issues by replacing the C-code with
>> the ready to use asm implementation from the kernel.
>>
>> Given that this code when written as C-code clearly is quite fragile
>> (also see the existing comments about the C-code being the way it is
>>   to get optimal assembly) and that we have a proven asm alternative,
>> I believe that this is the best solution.
>>
>> Note that we actually already have a copy of the kernel's
>> v7_flush_dcache_all() in arch/arm/mach-uniphier/arm32/lowlevel_init.S.
>>
>> We should replace that implementation with a call to this one, but I'm
>> leaving this up to people with access to actual unifier hw. With this
>> replacement in mind I've kept the original function as is, only renamed
>> it to __v7_flush_dcache_all and v7_flush_dcache_all is a wrapper
>> saving the registered clobbered by the core __v7_flush_dcache_all code
>>
>> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
>
> So I was able to talk with a few people and this is the right approach.
> The cache routines we're doing here in C must not in fact be done in C.
> That things work today with some compilers is not by design.  This is at
> least a minimally correct thing to do and a more correct thing to do
> would be to leverage more of the code from the kernel for cache
> functions (and not just for v7).

Thanks! I guess that means that we can consider this issue resolved?
Which is good news as this was a nasty bug to track down.

So are you planning on merging this patch / these 2 patches to
master then ?

Note that in my testing only the first patch is necessary to fix
various sunxi boards no longer booting.

Regards,

Hans