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

[Tom Rini <trini@konsulko.com>]

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@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).

-- 
Tom
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