[PATCH weston 2/2] compositor-drm: Fix inconsistency in finish frame timestamps

[Ander Conselvan de Oliveira]

The page flip event timestamps comes from the monotonic clock, while
idle_repaint() gets the time with gettimeofday(). That leads to
inconsistent timestamps on the frame callbacks.

Fix this by making the drm backend page flip to the current buffer and
call weston_output_finish_frame() with the page flip event timestamp,
instead of using gettimeofday().
---
 src/compositor-drm.c |   34 ++++++++++++++++++++++++++++++----
 src/compositor.c     |    6 +++++-
 src/compositor.h     |    1 +
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/src/compositor-drm.c b/src/compositor-drm.c
index f1f7343..e3ac572 100644
--- a/src/compositor-drm.c
+++ b/src/compositor-drm.c
@@ -629,6 +629,26 @@ drm_output_repaint(struct weston_output *output_base,
 }
 
 static void
+drm_output_start_repaint_loop(struct weston_output *output_base)
+{
+	struct drm_output *output = (struct drm_output *) output_base;
+	struct drm_compositor *compositor = (struct drm_compositor *)
+		output_base->compositor;
+	uint32_t fb_id;
+
+	if (output->current)
+		fb_id = output->current->fb_id;
+	else
+		fb_id = output->original_crtc->buffer_id;
+
+	if (drmModePageFlip(compositor->drm.fd, output->crtc_id, fb_id,
+			    DRM_MODE_PAGE_FLIP_EVENT, output) < 0) {
+		weston_log("queueing pageflip failed: %m\n");
+		return;
+	}
+}
+
+static void
 vblank_handler(int fd, unsigned int frame, unsigned int sec, unsigned int usec,
 	       void *data)
 {
@@ -655,11 +675,16 @@ page_flip_handler(int fd, unsigned int frame,
 	struct drm_output *output = (struct drm_output *) data;
 	uint32_t msecs;
 
-	output->page_flip_pending = 0;
+	/* We don't set page_flip_pending on start_repaint_loop, in that case
+	 * we just want to page flip to the current buffer to get an accurate
+	 * timestamp */
+	if (output->page_flip_pending) {
+		drm_output_release_fb(output, output->current);
+		output->current = output->next;
+		output->next = NULL;
+	}
 
-	drm_output_release_fb(output, output->current);
-	output->current = output->next;
-	output->next = NULL;
+	output->page_flip_pending = 0;
 
 	if (!output->vblank_pending) {
 		msecs = sec * 1000 + usec / 1000;
@@ -1636,6 +1661,7 @@ create_output_for_connector(struct drm_compositor *ec,
 	wl_list_insert(ec->base.output_list.prev, &output->base.link);
 
 	output->base.origin = output->base.current;
+	output->base.start_repaint_loop = drm_output_start_repaint_loop;
 	output->base.repaint = drm_output_repaint;
 	output->base.destroy = drm_output_destroy;
 	output->base.assign_planes = drm_assign_planes;
diff --git a/src/compositor.c b/src/compositor.c
index 764d622..a0faba1 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -1164,7 +1164,11 @@ idle_repaint(void *data)
 {
 	struct weston_output *output = data;
 
-	weston_output_finish_frame(output, weston_compositor_get_time());
+	if (output->start_repaint_loop)
+		output->start_repaint_loop(output);
+	else
+		weston_output_finish_frame(output,
+					   weston_compositor_get_time());
 }
 
 WL_EXPORT void
diff --git a/src/compositor.h b/src/compositor.h
index 004f931..34f81b5 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -181,6 +181,7 @@ struct weston_output {
 	struct weston_mode *origin;
 	struct wl_list mode_list;
 
+	void (*start_repaint_loop)(struct weston_output *output);
 	void (*repaint)(struct weston_output *output,
 			pixman_region32_t *damage);
 	void (*destroy)(struct weston_output *output);
-- 
1.7.10.4