From 047193a058a7c2e203cb2a75dbab36099220bf11 Mon Sep 17 00:00:00 2001
From: Derek Foreman <derek.foreman@collabora.com>
Date: Wed, 28 Jan 2026 14:56:03 -0600
Subject: [PATCH] compositor: Add REPAINT_DEFERRED repaint_status

Backends can end up in indeterminate/invalid state and be unable to
process updates.

Add a way for the backend to tell the core to stop scheduling repaints,
and a way for the backend to schedule all the repaints that should have
taken place during the invalid state period.

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>
---
 include/libweston/libweston.h  |  4 ++++
 libweston/backend.h            |  6 ++++++
 libweston/compositor.c         | 39 ++++++++++++++++++++++++++++++++++
 libweston/libweston-internal.h |  8 +++++++
 4 files changed, 57 insertions(+)

diff --git a/include/libweston/libweston.h b/include/libweston/libweston.h
index 5713a3e01..2c223c8f6 100644
--- a/include/libweston/libweston.h
+++ b/include/libweston/libweston.h
@@ -362,6 +362,10 @@ enum weston_repaint_status {
 	REPAINT_BEGIN_FROM_IDLE, /**< start_repaint_loop scheduled */
 	REPAINT_SCHEDULED, /**< repaint is scheduled to occur */
 	REPAINT_AWAITING_COMPLETION, /**< last repaint not yet finished */
+	/** Needs a repaint when the backend is ready. Backends must call
+	 *  weston_backend_clear_deferred() when ready.
+	 */
+	REPAINT_DEFERRED,
 };
 
 /** Content producer for heads
diff --git a/libweston/backend.h b/libweston/backend.h
index 3c3194a8c..b9229ef81 100644
--- a/libweston/backend.h
+++ b/libweston/backend.h
@@ -134,6 +134,12 @@ struct weston_backend {
 	 * defined in weston_compositor_backend.
 	 */
 	enum weston_compositor_backend backend_type;
+
+	/** The backend is incapable of painting right now, but will
+	 *  call weston_backend_clear_deferred() at some point to
+	 *  exit deferred state.
+	 */
+	bool deferred;
 };
 
 /* weston_head */
diff --git a/libweston/compositor.c b/libweston/compositor.c
index cbfb2cdac..159b8e602 100644
--- a/libweston/compositor.c
+++ b/libweston/compositor.c
@@ -4320,6 +4320,11 @@ weston_output_finish_frame(struct weston_output *output,
 	else
 		assert(presented_flags & WP_PRESENTATION_FEEDBACK_INVALID);
 
+	if (output->backend->deferred) {
+		output->repaint_status = REPAINT_DEFERRED;
+		return;
+	}
+
 	weston_compositor_read_presentation_clock(compositor, &now);
 
 	/* If we haven't been supplied any timestamp at all, we don't have a
@@ -4688,6 +4693,11 @@ weston_output_schedule_repaint(struct weston_output *output)
 	if (output->repaint_status != REPAINT_NOT_SCHEDULED)
 		return;
 
+	if (output->backend->deferred) {
+		output->repaint_status = REPAINT_DEFERRED;
+		return;
+	}
+
 	output->repaint_status = REPAINT_BEGIN_FROM_IDLE;
 	assert(!output->idle_repaint_source);
 	output->idle_repaint_source = wl_event_loop_add_idle(loop, idle_repaint,
@@ -9412,6 +9422,8 @@ output_repaint_status_text(struct weston_output *output)
 		return "repaint scheduled";
 	case REPAINT_AWAITING_COMPLETION:
 		return "awaiting completion";
+	case REPAINT_DEFERRED:
+		return "deferred";
 	}
 
 	assert(!"output_repaint_status_text missing enum");
@@ -9750,6 +9762,8 @@ weston_compositor_print_scene_graph(struct weston_compositor *ec)
 			fprintf(fp, "\tto be presented at: %" PRId64 ".%09ld\n",
 				(int64_t)output->next_present.tv_sec,
 				output->next_present.tv_nsec);
+		} else  if (output->repaint_status == REPAINT_DEFERRED) {
+			fprintf(fp, "\tDeferred pending backend recovery\n");
 		}
 		wl_list_for_each(head, &output->head_list, output_link) {
 			fprintf(fp, "\tHead %d (%s): %sconnected\n",
@@ -10920,3 +10934,28 @@ weston_output_set_ready(struct weston_output *output)
 		weston_output_schedule_repaint(output);
 	}
 }
+
+WL_EXPORT void
+weston_backend_set_deferred(struct weston_backend *backend)
+{
+	backend->deferred = true;
+}
+
+WL_EXPORT void
+weston_backend_clear_deferred(struct weston_backend *backend,
+			      struct weston_compositor *compositor)
+{
+	struct weston_output *output;
+
+	backend->deferred = false;
+
+	wl_list_for_each(output, &compositor->output_list, link) {
+		if (output->backend != backend)
+			continue;
+		if (output->repaint_status != REPAINT_DEFERRED)
+			continue;
+
+		output->repaint_status = REPAINT_NOT_SCHEDULED;
+		weston_output_schedule_repaint(output);
+	}
+}
diff --git a/libweston/libweston-internal.h b/libweston/libweston-internal.h
index 7ff673a91..76aae065a 100644
--- a/libweston/libweston-internal.h
+++ b/libweston/libweston-internal.h
@@ -876,4 +876,12 @@ struct timespec
 weston_output_repaint_from_present(const struct weston_output *output,
 				   const struct timespec *now,
 				   const struct timespec *present_time);
+
+void
+weston_backend_set_deferred(struct weston_backend *backend);
+
+void
+weston_backend_clear_deferred(struct weston_backend *backend,
+                              struct weston_compositor *compositor);
+
 #endif