On Sat, 30 May 2026 17:14:44 +0000 Simon Ser <[email protected]> wrote:
> Currently user-space can only request page-flip events for all CRTCs included > in an atomic commit. This is cumbersome with multi-CRTC commits: when moving a > plane from a different CRTC, or when disabling a plane, user-space has no way > to opt-out of the page-flip events. > > Additionally, page-flip events are invalid for already-disable planes, so Hi Simon, do you mean CRTCs? I find "already disabled" to be not really clear that you mean off->off transition. > user-space needs to add special cases [1]. Libraries cannot add planes to the > commit without risking causing unexpected page-flip events for the > compositor [2]. If a library adds a plane that is currently associated with another CRTC, would it not be a logic error in userspace if it didn't expect that CRTC to be involved? Mostly likely if it succeeds, the plane would disappear from its old CRTC unintended. If a CRTC is unexpectedly involved, userspace risks EBUSY when it wants to update that CRTC for real. > Figuring out what CRTCs get implicitly included in a commit is > non-trivial [3]. Yes, but is this actually helpful rather than making the failures more rare and harder to debug? > Introduce a new PAGE_FLIP_EVENT CRTC property so that user-space can select > explicitly which CRTCs will get page-flip events. The property is very > similar to IN_FENCE_FD/OUT_FENCE_PTR: it always reads as zero, and 1 can > be written to request an event. > > A user-space implementation is available at [4]. > > [1]: > https://github.com/ValveSoftware/gamescope/blob/67fcb3aebae0ae1eb2d1cff60f29e6d9fe1d128f/src/Backends/DRMBackend.cpp#L2897 > [2]: https://gitlab.freedesktop.org/emersion/libliftoff/-/merge_requests/85 > [3]: > https://lore.kernel.org/dri-devel/[email protected]/ > [4]: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/5387 > > Signed-off-by: Simon Ser <[email protected]> > Cc: Daniel Stone <[email protected]> > Cc: Michel Dänzer <[email protected]> > Cc: Pekka Paalanen <[email protected]> > Cc: Christian König <[email protected]> > Cc: Simona Vetter <[email protected]> > --- > drivers/gpu/drm/drm_atomic_uapi.c | 17 +++++++++++++++-- > drivers/gpu/drm/drm_crtc.c | 7 +++++++ > drivers/gpu/drm/drm_mode_config.c | 6 ++++++ > include/drm/drm_crtc.h | 6 ++++++ > include/drm/drm_mode_config.h | 4 ++++ > 5 files changed, 38 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/drm_atomic_uapi.c > b/drivers/gpu/drm/drm_atomic_uapi.c > index 6441b55cc274..21f2b0df4f63 100644 > --- a/drivers/gpu/drm/drm_atomic_uapi.c > +++ b/drivers/gpu/drm/drm_atomic_uapi.c > @@ -466,6 +466,14 @@ static int drm_atomic_crtc_set_property(struct drm_crtc > *crtc, > return -EFAULT; > > set_out_fence_for_crtc(state->state, crtc, fence_ptr); > + } else if (property == config->prop_page_flip_event) { > + if (val != 1) { > + drm_dbg_atomic(crtc->dev, > + "[CRTC:%d:%s] PAGE_FLIP_EVENT can only > be set to 1", > + crtc->base.id, crtc->name); > + return -EINVAL; > + } > + state->page_flip_event_requested = val; > } else if (property == crtc->scaling_filter_property) { > state->scaling_filter = val; > } else if (property == crtc->sharpness_strength_property) { > @@ -507,6 +515,8 @@ drm_atomic_crtc_get_property(struct drm_crtc *crtc, > *val = state->background_color; > else if (property == config->prop_out_fence_ptr) > *val = 0; > + else if (property == config->prop_page_flip_event) > + *val = 0; > else if (property == crtc->scaling_filter_property) > *val = state->scaling_filter; > else if (property == crtc->sharpness_strength_property) > @@ -1385,6 +1395,7 @@ static int prepare_signaling(struct drm_device *dev, > struct drm_connector *conn; > struct drm_connector_state *conn_state; > int i, c = 0, ret; > + bool page_flip_event_requested; > > if (arg->flags & DRM_MODE_ATOMIC_TEST_ONLY) > return 0; > @@ -1392,9 +1403,11 @@ static int prepare_signaling(struct drm_device *dev, > for_each_new_crtc_in_state(state, crtc, crtc_state, i) { > s32 __user *fence_ptr; > > + page_flip_event_requested = arg->flags & > DRM_MODE_PAGE_FLIP_EVENT || > + > crtc_state->page_flip_event_requested; > fence_ptr = get_out_fence_for_crtc(crtc_state->state, crtc); > > - if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT || fence_ptr) { > + if (page_flip_event_requested || fence_ptr) { > struct drm_pending_vblank_event *e; > > e = create_vblank_event(crtc, arg->user_data); > @@ -1404,7 +1417,7 @@ static int prepare_signaling(struct drm_device *dev, > crtc_state->event = e; > } > > - if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT) { > + if (page_flip_event_requested) { > struct drm_pending_vblank_event *e = crtc_state->event; > > if (!file_priv) > diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c > index 63ead8ba6756..5ad6681bd47c 100644 > --- a/drivers/gpu/drm/drm_crtc.c > +++ b/drivers/gpu/drm/drm_crtc.c > @@ -248,6 +248,11 @@ struct dma_fence *drm_crtc_create_fence(struct drm_crtc > *crtc) > * The sharpness effect takes place post blending on the final composed > output. > * If the feature is disabled, the content remains same without any > sharpening effect > * and when this feature is applied, it enhances the clarity of the > content. > + * PAGE_FLIP_EVENT: > + * Atomic property for requesting a page-flip event on this CRTC. > + * > + * The value of this property is an integer value which always reads as > + * zero and can be written with 1 to request the event. It took me a while to realise; should probably explain here that if one uses this, then they would not use DRM_MODE_PAGE_FLIP_EVENT at the same time. Does this allow asking for an event for a CRTC off->off transition? Thanks, pq > */ > > __printf(6, 0) > @@ -322,6 +327,8 @@ static int __drm_crtc_init_with_planes(struct drm_device > *dev, struct drm_crtc * > config->prop_out_fence_ptr, 0); > drm_object_attach_property(&crtc->base, > config->prop_vrr_enabled, 0); > + drm_object_attach_property(&crtc->base, > + config->prop_page_flip_event, 0); > } > > return 0; > diff --git a/drivers/gpu/drm/drm_mode_config.c > b/drivers/gpu/drm/drm_mode_config.c > index f432f485a914..688937d2e1ec 100644 > --- a/drivers/gpu/drm/drm_mode_config.c > +++ b/drivers/gpu/drm/drm_mode_config.c > @@ -496,6 +496,12 @@ static int drm_mode_create_standard_properties(struct > drm_device *dev) > return -ENOMEM; > dev->mode_config.prop_out_fence_ptr = prop; > > + prop = drm_property_create_range(dev, DRM_MODE_PROP_ATOMIC, > + "PAGE_FLIP_EVENT", 0, 1); > + if (!prop) > + return -ENOMEM; > + dev->mode_config.prop_page_flip_event = prop; > + > prop = drm_property_create_object(dev, DRM_MODE_PROP_ATOMIC, > "CRTC_ID", DRM_MODE_OBJECT_CRTC); > if (!prop) > diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h > index 152349f973e3..b0f9130d263a 100644 > --- a/include/drm/drm_crtc.h > +++ b/include/drm/drm_crtc.h > @@ -311,6 +311,12 @@ struct drm_crtc_state { > */ > bool vrr_enabled; > > + /** > + * @page_flip_event_requested: indicates whether a page-flip event has > + * been requested on this CRTC. > + */ > + bool page_flip_event_requested; > + > /** > * @self_refresh_active: > * > diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h > index d8f5b7e9673e..13f39677c32f 100644 > --- a/include/drm/drm_mode_config.h > +++ b/include/drm/drm_mode_config.h > @@ -670,6 +670,10 @@ struct drm_mode_config { > * value of type s32, and then cast that pointer to u64. > */ > struct drm_property *prop_out_fence_ptr; > + /** > + * @page_flip_event_property: property to request page-flip events. > + */ > + struct drm_property *prop_page_flip_event; > /** > * @prop_crtc_id: Default atomic plane property to specify the > * &drm_crtc.
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