linux-kernel - Re: [PATCH] drm: enable uncached DMA optimization for ARM and arm64

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Date:   Wed, 6 Feb 2019 19:38:34 +0100
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Koenig, Christian" <christian.koenig@....com>
Cc:     Will Deacon <will.deacon@....com>,
        Carsten Haitzler <Carsten.Haitzler@....com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        David Airlie <airlied@...ux.ie>,
        "Daenzer, Michel" <Michel.Daenzer@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Zhang, Jerry" <Jerry.Zhang@....com>,
        "Huang, Ray" <Ray.Huang@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Alex Deucher <alexdeucher@...il.com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        Sean Paul <sean@...rly.run>,
        "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 06.02.19 um 18:23 schrieb Ard Biesheuvel:
> On Fri, 25 Jan 2019 at 11:35, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:
>> On Fri, 25 Jan 2019 at 12:30, Christian König
>> <ckoenig.leichtzumerken@...il.com> wrote:
>>> 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.
>>>
>> Wonderful, thanks.
> Hi Christian,
>
> Are you still planning to merge this for v5.1?

My bad, only pushed this to our internal branch, but forgot out 
drm-misc-next.

Fixed now, thanks for the reminder.

Christian.

>
> Thanks,
> Ard.
> _______________________________________________
> amd-gfx mailing list
> amd-gfx@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/amd-gfx

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