Re: [PATCH v2] drm/amdgpu/dc: Require primary plane to be enabled whenever the CRTC is

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On 2020-09-14 4:37 p.m., Kazlauskas, Nicholas wrote:
On 2020-09-14 3:52 a.m., Michel Dänzer wrote:
On 2020-09-07 9:57 a.m., Daniel Vetter wrote:
On Fri, Sep 04, 2020 at 12:43:04PM +0200, Michel Dänzer wrote:
From: Michel Dänzer <mdaenzer@xxxxxxxxxx>

Don't check drm_crtc_state::active for this either, per its
documentation in include/drm/drm_crtc.h:

  * Hence drivers must not consult @active in their various
  * &drm_mode_config_funcs.atomic_check callback to reject an atomic
  * commit.

atomic_remove_fb disables the CRTC as needed for disabling the primary
plane.

This prevents at least the following problems if the primary plane gets
disabled (e.g. due to destroying the FB assigned to the primary plane,
as happens e.g. with mutter in Wayland mode):

* The legacy cursor ioctl returned EINVAL for a non-0 cursor FB ID
   (which enables the cursor plane).
* If the cursor plane was enabled, changing the legacy DPMS property
   value from off to on returned EINVAL.

v2:
* Minor changes to code comment and commit log, per review feedback.

GitLab: https://gitlab.gnome.org/GNOME/mutter/-/issues/1108
GitLab: https://gitlab.gnome.org/GNOME/mutter/-/issues/1165
GitLab: https://gitlab.gnome.org/GNOME/mutter/-/issues/1344
Suggested-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Michel Dänzer <mdaenzer@xxxxxxxxxx>

Commit message agrees with my understand of this maze now, so:

Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

Thanks Daniel!


Nick / Harry, any more feedback? If not, can you apply this?


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).


Maybe for now this can go in and if something breaks we can deal with the fallout then. 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.


Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@xxxxxxx>

Thanks!


--
Earthling Michel Dänzer               |               https://redhat.com
Libre software enthusiast             |             Mesa and X developer
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