From mboxrd@z Thu Jan  1 00:00:00 1970
From: catalin.marinas@arm.com (Catalin Marinas)
Date: Thu, 7 Nov 2013 09:47:05 +0000
Subject: [PATCH] arm64: enable EDAC on arm64
In-Reply-To: <CAL_JsqLwFHeRZzaMAxNmPSfNeVb_W2Ng=mXBkyUPQx+=beHyTg@mail.gmail.com>
References: <1383742944-28059-1-git-send-email-robherring2@gmail.com>
 <20131106152608.GD979@arm.com>
 <CAL_JsqLwFHeRZzaMAxNmPSfNeVb_W2Ng=mXBkyUPQx+=beHyTg@mail.gmail.com>
Message-ID: <20131107094705.GB13674@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, Nov 06, 2013 at 06:39:18PM +0000, Rob Herring wrote:
> On Wed, Nov 6, 2013 at 9:26 AM, Catalin Marinas <catalin.marinas@arm.com> wrote:
> > On Wed, Nov 06, 2013 at 01:02:24PM +0000, Rob Herring wrote:
> >> +static inline void atomic_scrub(void *va, u32 size)
> >> +{
> >> +     unsigned int *virt_addr = va;
> >> +     unsigned int temp, temp2;
> >> +     unsigned int i;
> >> +
> >> +     for (i = 0; i < size / sizeof(*virt_addr); i++, virt_addr++) {
> >> +             /*
> >> +              * No need to check for store failure, another write means
> >> +              * the scrubbing has effectively already been done for us.
> >> +              */
> >> +             asm volatile("\n"
> >> +                     "       ldxr    %0, %2\n"
> >> +                     "       stxr    %w1, %0, %2\n"
> >> +                     : "=&r" (temp), "=&r" (temp2), "+Q" (virt_addr)
> >> +                     : : "cc");
> >
> > But failure of stxr does not necessarily mean another write. It can be
> > an interrupt, cache line migration etc. The exclusive monitor can be
> > emulated in many ways.
> 
> Right, I was thinking I could simplify things.
> 
> In that case, I could implement this with just "atomic64_add(0,
> virt_addr)", but is there any guarantee that atomic64_t has a size of
> 8 bytes and that I can simply increment an atomic64_t ptr?

I would rather add just an asm volatile (as you've done) to avoid the
'add' inside the loop and force casting to atomic64_t.

-- 
Catalin