drm: renesas: shmobile: Wait for page flip when turning CRTC off

Turning a CRTC off will prevent a queued page flip from ever completing,
potentially confusing userspace.  Wait for queued page flips to complete
before turning the CRTC off to avoid this.
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/c97d5859c43fa36043c61de28d67688ebe345092.1694767209.git.geert+renesas@glider.be

drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c

@@ -50,11 +50,40 @@ void shmob_drm_crtc_finish_page_flip(struct shmob_drm_crtc *scrtc)
 	scrtc->event = NULL;
 	if (event) {
 		drm_crtc_send_vblank_event(&scrtc->base, event);
+		wake_up(&scrtc->flip_wait);
 		drm_crtc_vblank_put(&scrtc->base);
 	}
 	spin_unlock_irqrestore(&dev->event_lock, flags);
 }
 
+static bool shmob_drm_crtc_page_flip_pending(struct shmob_drm_crtc *scrtc)
+{
+	struct drm_device *dev = scrtc->base.dev;
+	unsigned long flags;
+	bool pending;
+
+	spin_lock_irqsave(&dev->event_lock, flags);
+	pending = scrtc->event != NULL;
+	spin_unlock_irqrestore(&dev->event_lock, flags);
+
+	return pending;
+}
+
+static void shmob_drm_crtc_wait_page_flip(struct shmob_drm_crtc *scrtc)
+{
+	struct drm_crtc *crtc = &scrtc->base;
+	struct shmob_drm_device *sdev = to_shmob_device(crtc->dev);
+
+	if (wait_event_timeout(scrtc->flip_wait,
+			       !shmob_drm_crtc_page_flip_pending(scrtc),
+			       msecs_to_jiffies(50)))
+		return;
+
+	dev_warn(sdev->dev, "page flip timeout\n");
+
+	shmob_drm_crtc_finish_page_flip(scrtc);
+}
+
 /* -----------------------------------------------------------------------------
  * CRTC
  */
@@ -253,6 +282,12 @@ static void shmob_drm_crtc_stop(struct shmob_drm_crtc *scrtc)
 	if (!scrtc->started)
 		return;
 
+	/*
+	 * Wait for page flip completion before stopping the CRTC as userspace
+	 * expects page flips to eventually complete.
+	 */
+	shmob_drm_crtc_wait_page_flip(scrtc);
+
 	/* Stop the LCDC. */
 	shmob_drm_crtc_start_stop(scrtc, false);
 
@@ -463,6 +498,8 @@ int shmob_drm_crtc_create(struct shmob_drm_device *sdev)
 	unsigned int i;
 	int ret;
 
+	init_waitqueue_head(&sdev->crtc.flip_wait);
+
 	sdev->crtc.dpms = DRM_MODE_DPMS_OFF;
 
 	primary = shmob_drm_plane_create(sdev, DRM_PLANE_TYPE_PRIMARY, 0);

drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.h

@@ -14,6 +14,8 @@
 #include <drm/drm_connector.h>
 #include <drm/drm_encoder.h>
 
+#include <linux/wait.h>
+
 #include <video/videomode.h>
 
 struct drm_pending_vblank_event;
@@ -24,6 +26,7 @@ struct shmob_drm_crtc {
 	struct drm_crtc base;
 
 	struct drm_pending_vblank_event *event;
+	wait_queue_head_t flip_wait;
 	int dpms;
 
 	const struct shmob_drm_format_info *format;