Message-ID: <961e758d-b0a0-8f6c-a8fa-c3047e058706@gmail.com>
Date:   Fri, 25 Jan 2019 12:30:23 +0100
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Alex Deucher <alexdeucher@...il.com>
Cc:     "Daenzer, Michel" <Michel.Daenzer@....com>,
        Carsten Haitzler <Carsten.Haitzler@....com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "Zhang, Jerry" <Jerry.Zhang@....com>,
        Christoph Hellwig <hch@...radead.org>,
        David Airlie <airlied@...ux.ie>,
        "Huang, Ray" <Ray.Huang@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Will Deacon <will.deacon@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        Sean Paul <sean@...rly.run>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH] drm: enable uncached DMA optimization for ARM and arm64

Am 25.01.19 um 09:43 schrieb Ard Biesheuvel:
> On Thu, 24 Jan 2019 at 15:01, Alex Deucher <alexdeucher@...il.com> wrote:
>> On Thu, Jan 24, 2019 at 9:00 AM Ard Biesheuvel
>> <ard.biesheuvel@...aro.org> wrote:
>>> On Thu, 24 Jan 2019 at 13:31, Koenig, Christian
>>> <Christian.Koenig@....com> wrote:
>>>> Am 24.01.19 um 13:06 schrieb Ard Biesheuvel:
>>>>> The DRM driver stack is designed to work with cache coherent devices
>>>>> only, but permits an optimization to be enabled in some cases, where
>>>>> for some buffers, both the CPU and the GPU use uncached mappings,
>>>>> removing the need for DMA snooping and allocation in the CPU caches.
>>>>>
>>>>> The use of uncached GPU mappings relies on the correct implementation
>>>>> of the PCIe NoSnoop TLP attribute by the platform, otherwise the GPU
>>>>> will use cached mappings nonetheless. On x86 platforms, this does not
>>>>> seem to matter, as uncached CPU mappings will snoop the caches in any
>>>>> case. However, on ARM and arm64, enabling this optimization on a
>>>>> platform where NoSnoop is ignored results in loss of coherency, which
>>>>> breaks correct operation of the device. Since we have no way of
>>>>> detecting whether NoSnoop works or not, just disable this
>>>>> optimization entirely for ARM and arm64.
>>>>>
>>>>> Cc: Christian Koenig <christian.koenig@....com>
>>>>> Cc: Alex Deucher <alexander.deucher@....com>
>>>>> Cc: David Zhou <David1.Zhou@....com>
>>>>> Cc: Huang Rui <ray.huang@....com>
>>>>> Cc: Junwei Zhang <Jerry.Zhang@....com>
>>>>> Cc: Michel Daenzer <michel.daenzer@....com>
>>>>> Cc: David Airlie <airlied@...ux.ie>
>>>>> Cc: Daniel Vetter <daniel@...ll.ch>
>>>>> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
>>>>> Cc: Maxime Ripard <maxime.ripard@...tlin.com>
>>>>> Cc: Sean Paul <sean@...rly.run>
>>>>> Cc: Michael Ellerman <mpe@...erman.id.au>
>>>>> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>>>>> Cc: Will Deacon <will.deacon@....com>
>>>>> Cc: Christoph Hellwig <hch@...radead.org>
>>>>> Cc: Robin Murphy <robin.murphy@....com>
>>>>> Cc: amd-gfx list <amd-gfx@...ts.freedesktop.org>
>>>>> Cc: dri-devel <dri-devel@...ts.freedesktop.org>
>>>>> Reported-by: Carsten Haitzler <Carsten.Haitzler@....com>
>>>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>>>> The subject line should probably read "disable uncached...".
>>>>
>>> Ugh, of course ...
>>>
>>>> With that fixed the patch is Reviewed-by: Christian König
>>>> <christian.koenig@....com>.
>>>>
>> Same:
>> Reviewed-by: Alex Deucher <alexander.deucher@....com>
>>
> Thanks all
>
> Should I resend the patch with the subject corrected?

I will update the subject line and push it upstream through 
drm-misc-next if nobody objects.

Christian.

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