From 8e5f68833dd8af5faefc8c235732f6043da4112b Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Sat, 30 May 2026 19:07:51 +0200
Subject: [PATCH] backend/drm: add support for PAGE_FLIP_EVENT property

---
 backend/drm/atomic.c             |  4 ++++
 backend/drm/drm.c                | 41 +++++++++++++++++++++++++-------
 backend/drm/properties.c         |  1 +
 include/backend/drm/drm.h        |  1 +
 include/backend/drm/properties.h |  1 +
 5 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/backend/drm/atomic.c b/backend/drm/atomic.c
index daa8ba9bf..c68e30670 100644
--- a/backend/drm/atomic.c
+++ b/backend/drm/atomic.c
@@ -582,6 +582,10 @@ static void atomic_connector_add(struct atomic *atom,
 		if (crtc->props.vrr_enabled != 0) {
 			atomic_add(atom, crtc->id, crtc->props.vrr_enabled, state->vrr_enabled);
 		}
+		if (crtc->props.page_flip_event && state->page_flip_event) {
+			wlr_log(WLR_DEBUG, "YAAAY");
+			atomic_add(atom, crtc->id, crtc->props.page_flip_event, 1);
+		}
 
 		set_plane_props(atom, drm, crtc->primary, state->primary_fb, crtc->id,
 			&state->primary_viewport.dst_box, &state->primary_viewport.src_box);
diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index d2f75f71f..2bff00bf6 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -503,7 +503,7 @@ void drm_page_flip_destroy(struct wlr_drm_page_flip *page_flip) {
 }
 
 static struct wlr_drm_page_flip *drm_page_flip_create(struct wlr_drm_backend *drm,
-		const struct wlr_drm_device_state *state) {
+		const struct wlr_drm_device_state *state, uint32_t flags) {
 	struct wlr_drm_page_flip *page_flip = calloc(1, sizeof(*page_flip));
 	if (page_flip == NULL) {
 		return NULL;
@@ -516,7 +516,11 @@ static struct wlr_drm_page_flip *drm_page_flip_create(struct wlr_drm_backend *dr
 		return NULL;
 	}
 	for (size_t i = 0; i < state->connectors_len; i++) {
-		struct wlr_drm_connector *conn = state->connectors[i].connector;
+		const struct wlr_drm_connector_state *conn_state = &state->connectors[i];
+		struct wlr_drm_connector *conn = conn_state->connector;
+		if (!(flags & DRM_MODE_PAGE_FLIP_EVENT) && !conn_state->page_flip_event) {
+			continue;
+		}
 		page_flip->connectors[i] = (struct wlr_drm_page_flip_connector){
 			.connector = conn,
 			.crtc_id = conn->crtc->id,
@@ -632,6 +636,16 @@ static void drm_connector_rollback_commit(const struct wlr_drm_connector_state *
 	}
 }
 
+static bool device_state_has_conn_page_flip_event(const struct wlr_drm_device_state *state) {
+	for (size_t i = 0; i < state->connectors_len; i++) {
+		const struct wlr_drm_connector_state *conn_state = &state->connectors[i];
+		if (conn_state->page_flip_event) {
+			return true;
+		}
+	}
+	return false;
+}
+
 static bool drm_commit(struct wlr_drm_backend *drm,
 		const struct wlr_drm_device_state *state,
 		uint32_t flags, bool test_only) {
@@ -639,8 +653,8 @@ static bool drm_commit(struct wlr_drm_backend *drm,
 	assert((flags & ~DRM_MODE_PAGE_FLIP_FLAGS) == 0);
 
 	struct wlr_drm_page_flip *page_flip = NULL;
-	if (flags & DRM_MODE_PAGE_FLIP_EVENT) {
-		page_flip = drm_page_flip_create(drm, state);
+	if ((flags & DRM_MODE_PAGE_FLIP_EVENT) || device_state_has_conn_page_flip_event(state)) {
+		page_flip = drm_page_flip_create(drm, state, flags);
 		if (page_flip == NULL) {
 			return false;
 		}
@@ -998,7 +1012,11 @@ static bool drm_connector_commit_state(struct wlr_drm_connector *conn,
 
 	uint32_t flags = 0;
 	if (!test_only && pending.active) {
-		flags |= DRM_MODE_PAGE_FLIP_EVENT;
+		if (conn->crtc->props.page_flip_event) {
+			pending.page_flip_event = true;
+		} else {
+			flags |= DRM_MODE_PAGE_FLIP_EVENT;
+		}
 	}
 	if (pending.base->tearing_page_flip) {
 		flags |= DRM_MODE_PAGE_FLIP_ASYNC;
@@ -1943,6 +1961,7 @@ bool commit_drm_device(struct wlr_drm_backend *drm,
 
 	bool ok = false;
 	bool modeset = false;
+	uint32_t flags = 0;
 	size_t conn_states_len = 0;
 	for (size_t i = 0; i < output_states_len; i++) {
 		const struct wlr_backend_output_state *output_state = &output_states[i];
@@ -1975,6 +1994,14 @@ bool commit_drm_device(struct wlr_drm_backend *drm,
 		}
 
 		modeset |= output_state->base.allow_reconfiguration;
+
+		if (!test_only) {
+			if (conn->crtc->props.page_flip_event) {
+				conn_state->page_flip_event = true;
+			} else {
+				flags |= DRM_MODE_PAGE_FLIP_EVENT;
+			}
+		}
 	}
 
 	if (test_only && drm->mgpu_renderer.wlr_rend) {
@@ -1984,10 +2011,6 @@ bool commit_drm_device(struct wlr_drm_backend *drm,
 		goto out;
 	}
 
-	uint32_t flags = 0;
-	if (!test_only) {
-		flags |= DRM_MODE_PAGE_FLIP_EVENT;
-	}
 	struct wlr_drm_device_state dev_state = {
 		.modeset = modeset,
 		.connectors = conn_states,
diff --git a/backend/drm/properties.c b/backend/drm/properties.c
index 4c6bdcb36..4f6bda161 100644
--- a/backend/drm/properties.c
+++ b/backend/drm/properties.c
@@ -44,6 +44,7 @@ static const struct prop_info crtc_info[] = {
 	{ "GAMMA_LUT_SIZE", INDEX(gamma_lut_size) },
 	{ "MODE_ID", INDEX(mode_id) },
 	{ "OUT_FENCE_PTR", INDEX(out_fence_ptr) },
+	{ "PAGE_FLIP_EVENT", INDEX(page_flip_event) },
 	{ "VRR_ENABLED", INDEX(vrr_enabled) },
 #undef INDEX
 };
diff --git a/include/backend/drm/drm.h b/include/backend/drm/drm.h
index a8c5e077a..16dd26cde 100644
--- a/include/backend/drm/drm.h
+++ b/include/backend/drm/drm.h
@@ -164,6 +164,7 @@ struct wlr_drm_connector_state {
 	bool vrr_enabled;
 	uint32_t colorspace;
 	uint32_t hdr_output_metadata;
+	bool page_flip_event;
 };
 
 /**
diff --git a/include/backend/drm/properties.h b/include/backend/drm/properties.h
index 20e0a5bff..f47b2695d 100644
--- a/include/backend/drm/properties.h
+++ b/include/backend/drm/properties.h
@@ -41,6 +41,7 @@ struct wlr_drm_crtc_props {
 	uint32_t active;
 	uint32_t mode_id;
 	uint32_t out_fence_ptr;
+	uint32_t page_flip_event;
 };
 
 struct wlr_drm_plane_props {