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

[Tom Rini]

On Wed, Apr 06, 2016 at 05:22:25PM +0200, Hans de Goede wrote:
> 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.

Yes it was, good job btw.

> 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.

We need at least a v2 to fix the build issue Masahiro pointed out.  But
yes, I'll tkae these two and put the rest on my TODO list.  Thanks!

-- 
Tom
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