[PATCH v2] drm/amdgpu/dc: Require primary plane to be enabled whenever the CRTC is
Michel Dänzer
michel at daenzer.net
Mon Sep 14 15:44:30 UTC 2020
On 2020-09-14 5:33 p.m., Kazlauskas, Nicholas wrote:
> On 2020-09-14 11:22 a.m., Michel Dänzer wrote:
>> On 2020-09-14 4:37 p.m., Kazlauskas, Nicholas wrote:
>>> On 2020-09-14 3:52 a.m., Michel Dänzer wrote:
>>>>
>>>> P.S. Since DCN doesn't make a distinction between primary or overlay
>>>> planes in hardware, could ChromiumOS achieve the same effect with
>>>> only the primary plane instead of only an overlay plane? If so,
>>>> maybe there's no need for the "black plane hack".
>>>>
>>>>
>>>
>>> I only know that atomictest tries to enable this configuration. Not
>>> sure if ChromiumOS or other "real" userspace tries this configuration.
>>
>> Someone mentioned that ChromiumOS uses this for video playback with
>> black bars (when the video aspect ratio doesn't match the display's).
>
> We only expose support for NV12 on the primary plane so we wouldn't be
> hitting this case at least.
Interesting, so if we're lucky this really won't affect any real-world apps.
>>> We can always go back to lying to userspace about the cursor being
>>> visible if the commit fails in that case I guess [...]
>>
>> I'm not sure what you mean by that / how it could work.
>
> Dropping the check you added in this patch:
>
> + if (state->enable &&
> + !(state->plane_mask & drm_plane_mask(crtc->primary)))
> return -EINVAL;
>
> That way we can still allow the cursor plane to be enabled while
> primary/overlay are not, it's just not going to be actually visible on
> the screen. It'll fail some IGT tests but nothing really uses this
> configuration as more than just a temporary state.
As Daniel pointed out in <20200901075432.GW2352366 at phenom.ffwll.local>
in the v1 patch thread, that won't fly, since atomic userspace can
legitimately expect the cursor plane to be visible in that case.
--
Earthling Michel Dänzer | https://redhat.com
Libre software enthusiast | Mesa and X developer
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