[PATCH] drm: enable uncached DMA optimization for ARM and arm64

[Christian König]

Am 06.02.19 um 18:23 schrieb Ard Biesheuvel:
> On Fri, 25 Jan 2019 at 11:35, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
>> On Fri, 25 Jan 2019 at 12:30, Christian König
>> <ckoenig.leichtzumerken at gmail.com> wrote:
>>> Am 25.01.19 um 09:43 schrieb Ard Biesheuvel:
>>>> On Thu, 24 Jan 2019 at 15:01, Alex Deucher <alexdeucher at gmail.com> wrote:
>>>>> On Thu, Jan 24, 2019 at 9:00 AM Ard Biesheuvel
>>>>> <ard.biesheuvel at linaro.org> wrote:
>>>>>> On Thu, 24 Jan 2019 at 13:31, Koenig, Christian
>>>>>> <Christian.Koenig at amd.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 at amd.com>
>>>>>>>> Cc: Alex Deucher <alexander.deucher at amd.com>
>>>>>>>> Cc: David Zhou <David1.Zhou at amd.com>
>>>>>>>> Cc: Huang Rui <ray.huang at amd.com>
>>>>>>>> Cc: Junwei Zhang <Jerry.Zhang at amd.com>
>>>>>>>> Cc: Michel Daenzer <michel.daenzer at amd.com>
>>>>>>>> Cc: David Airlie <airlied at linux.ie>
>>>>>>>> Cc: Daniel Vetter <daniel at ffwll.ch>
>>>>>>>> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>>>>>>>> Cc: Maxime Ripard <maxime.ripard at bootlin.com>
>>>>>>>> Cc: Sean Paul <sean at poorly.run>
>>>>>>>> Cc: Michael Ellerman <mpe at ellerman.id.au>
>>>>>>>> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
>>>>>>>> Cc: Will Deacon <will.deacon at arm.com>
>>>>>>>> Cc: Christoph Hellwig <hch at infradead.org>
>>>>>>>> Cc: Robin Murphy <robin.murphy at arm.com>
>>>>>>>> Cc: amd-gfx list <amd-gfx at lists.freedesktop.org>
>>>>>>>> Cc: dri-devel <dri-devel at lists.freedesktop.org>
>>>>>>>> Reported-by: Carsten Haitzler <Carsten.Haitzler at arm.com>
>>>>>>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>>>>>>> The subject line should probably read "disable uncached...".
>>>>>>>
>>>>>> Ugh, of course ...
>>>>>>
>>>>>>> With that fixed the patch is Reviewed-by: Christian König
>>>>>>> <christian.koenig at amd.com>.
>>>>>>>
>>>>> Same:
>>>>> Reviewed-by: Alex Deucher <alexander.deucher at amd.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.
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