[PATCH] drm/atomic: introduce PAGE_FLIP_EVENT property

[PATCH] drm/atomic: introduce PAGE_FLIP_EVENT property

[Simon Ser]

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
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]. Figuring out what CRTCs get implicitly included in a commit is
non-trivial [3].

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/20250501112945.6448-1-contact@emersion.fr/
[4]: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/5387

Signed-off-by: Simon Ser <contact@emersion.fr>
Cc: Daniel Stone <daniel@fooishbar.org>
Cc: Michel Dänzer <michel.daenzer@mailbox.org>
Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Simona Vetter <simona@ffwll.ch>
---
 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.
  */
 
 __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.
-- 
2.54.0

Re: [PATCH] drm/atomic: introduce PAGE_FLIP_EVENT property

[Xaver Hugl]

+1, this is very useful. A KWin implementation for this is at
https://invent.kde.org/plasma/kwin/-/merge_requests/9308

- Xaver

Re: [PATCH] drm/atomic: introduce PAGE_FLIP_EVENT property

[Simon Ser]

IGT test available here:
https://lists.freedesktop.org/archives/igt-dev/2026-May/111026.html

Re: [PATCH] drm/atomic: introduce PAGE_FLIP_EVENT property

[Pekka Paalanen]

[-- Attachment #1: Type: text/plain, Size: 8221 bytes --]

On Sat, 30 May 2026 17:14:44 +0000
Simon Ser <contact@emersion.fr> 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/20250501112945.6448-1-contact@emersion.fr/
> [4]: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/5387
> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Cc: Daniel Stone <daniel@fooishbar.org>
> Cc: Michel Dänzer <michel.daenzer@mailbox.org>
> Cc: Pekka Paalanen <pekka.paalanen@collabora.com>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Simona Vetter <simona@ffwll.ch>
> ---
>  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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Re: [PATCH] drm/atomic: introduce PAGE_FLIP_EVENT property

[Simon Ser]

On Tuesday, June 16th, 2026 at 13:16, Pekka Paalanen <pekka.paalanen@collabora.com> wrote:

> On Sat, 30 May 2026 17:14:44 +0000
> Simon Ser <contact@emersion.fr> 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.

Oh, yeah, indeed!

> > 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.

The plane is involved anyways, and the library can figure that out. The
library is fully managing the plane, and has ensured it's turned off
before migrating it to a new CRTC. What's unexpected and unavoidable is
the page-flip event on the old CRTC.

> > 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?

I don't believe spurious page-flip events help that much in that regard
TBH. This only helps if the page-flip flag is on and user-space didn't
mean to include these other CRTCs. The benefits of the new API outweigh
the small cost of sometimes finding a bug a bit quicker. If some
user-space believes otherwise, they can still keep using the old global
flag.

> > 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.

Right.

> Does this allow asking for an event for a CRTC off->off
> transition?

It does not.

Re: [PATCH] drm/atomic: introduce PAGE_FLIP_EVENT property

[Pekka Paalanen]

[-- Attachment #1: Type: text/plain, Size: 3858 bytes --]

On Thu, 23 Jul 2026 16:02:48 +0000
Simon Ser <contact@emersion.fr> wrote:

> On Tuesday, June 16th, 2026 at 13:16, Pekka Paalanen <pekka.paalanen@collabora.com> wrote:
> 
> > On Sat, 30 May 2026 17:14:44 +0000
> > Simon Ser <contact@emersion.fr> 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.  
> 
> Oh, yeah, indeed!
> 
> > > 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.  
> 
> The plane is involved anyways, and the library can figure that out. The
> library is fully managing the plane, and has ensured it's turned off
> before migrating it to a new CRTC. What's unexpected and unavoidable is
> the page-flip event on the old CRTC.

Hi,

do you mean it currently works like this:

0. The plane is active on CRTC A.
1. Submit update 1 with CRTC A, turn the plane off on CRTC A.
2. Update 1 completes, and delivers its pageflip event.
3. Submit update 2 with CRTC B, turn the plane on on CRTC B.
4. Update 2 completes and delivers pageflip events on *both* CRTC B and A?

You want to prevent the pageflip event from CRTC A in step 4?

Or what is the scenario you have in mind?


Thanks,
pq

> > > 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?  
> 
> I don't believe spurious page-flip events help that much in that regard
> TBH. This only helps if the page-flip flag is on and user-space didn't
> mean to include these other CRTCs. The benefits of the new API outweigh
> the small cost of sometimes finding a bug a bit quicker. If some
> user-space believes otherwise, they can still keep using the old global
> flag.
> 
> > > 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.  
> 
> Right.
> 
> > Does this allow asking for an event for a CRTC off->off
> > transition?  
> 
> It does not.


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