linux-kernel - Re: framebuffer corruption due to overlapping stp instructions on arm64

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Message-ID: <20180803094129.GB17798@arm.com>
Date:   Fri, 3 Aug 2018 10:41:30 +0100
From:   Will Deacon <will.deacon@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Mikulas Patocka <mpatocka@...hat.com>,
        Matt Sealey <neko@...uhatsu.net>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        libc-alpha@...rceware.org,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: framebuffer corruption due to overlapping stp instructions on
 arm64

On Fri, Aug 03, 2018 at 09:16:39AM +0200, Ard Biesheuvel wrote:
> On 3 August 2018 at 08:35, Mikulas Patocka <mpatocka@...hat.com> wrote:
> >
> >
> > On Thu, 2 Aug 2018, Matt Sealey wrote:
> >
> >> The easiest explanation for this would be that the memory isn?t mapped
> >> correctly. You can?t use PCIe memory spaces with anything other than
> >> Device-nGnRE or stricter mappings. That?s just differences between the
> >> AMBA and PCIe (posted/unposted) memory models.
> 
> Whoa hold on there.
> 
> Are you saying we cannot have PCIe BAR windows with memory semantics on ARM?
> 
> Most accelerated graphics drivers rely heavily on the ability to map
> the VRAM normal-non-cacheable (ioremap_wc, basically), and treat it as
> ordinary memory.

Yeah, I'd expect framebuffers to be mapped as normal NC. That should be
fine for prefetchable BARs, no?

Will