[PATCH] drm: document DRM_MODE_PAGE_FLIP_EVENT interactions with atomic

[Pekka Paalanen]

On Thu, 16 Jan 2025 16:25:35 +0000
Simon Ser <contact at emersion.fr> wrote:

> It's not obvious off-hand which CRTCs will get a page-flip event
> when using this flag in an atomic commit, because it's all
> implicitly implied based on the contents of the atomic commit.
> Document requirements for using this flag and
> 

and?

> Note, because prepare_signaling() runs right after
> drm_atomic_set_property() calls, page-flip events are not delivered
> for CRTCs pulled in later by DRM core (e.g. on modeset by
> drm_atomic_helper_check_modeset()) or the driver (e.g. other CRTCs
> sharing a DP-MST connector).
> 
> Signed-off-by: Simon Ser <contact at emersion.fr>
> Cc: Simona Vetter <simona.vetter at ffwll.ch>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Pekka Paalanen <pekka.paalanen at collabora.com>
> Cc: David Turner <david.turner at raspberrypi.com>
> ---
>  include/uapi/drm/drm_mode.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index c082810c08a8..a122bea25593 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -962,6 +962,14 @@ struct hdr_output_metadata {
>   * Request that the kernel sends back a vblank event (see
>   * struct drm_event_vblank) with the &DRM_EVENT_FLIP_COMPLETE type when the
>   * page-flip is done.
> + *
> + * When used with atomic uAPI, one event will be delivered per CRTC included in
> + * the atomic commit. A CRTC is included in an atomic commit if one of its
> + * properties is set, or if a property is set on a connector or plane linked
> + * via the CRTC_ID property to the CRTC. At least one CRTC must be included,
> + * and all pulled in CRTCs must be either previously or newly powered on (in
> + * other words, a powered off CRTC which stays off cannot be included in the
> + * atomic commit).

Sounds right. I imagine this doc needs to be extended when drm_colorop
lands, as yet another way to pull in a CRTC.

Wasn't this also conditional on the DRM_CAP_CRTC_IN_VBLANK_EVENT or did
userspace really need to count the events even without it?

Nevertheless, should there be a "see also DRM_CAP_CRTC_IN_VBLANK_EVENT"?

>   */
>  #define DRM_MODE_PAGE_FLIP_EVENT 0x01
>  /**

Thanks,
pq
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