sna: Avoid confusing failure to flip and flipping zero CRTC

During the present unflip path we blindly try to restore the original
mode after a flip failure. However, it confuses flipping zero CRTC with
a genuine failure. This has the result of undoing a DPMS change (e.g.
xset dpms force dpms) under a DRI3 compositor.

Reported-by: Jiri Slaby <jirislaby@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=81456
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

3 files changed, 22 insertions, 12 deletions

diff --git a/src/sna/sna_display.c b/src/sna/sna_display.c
index 747d261f..7c70b4cc 100644
--- a/src/sna/sna_display.c
+++ b/src/sna/sna_display.c
@@ -4863,6 +4863,8 @@ sna_page_flip(struct sna *sna,
 	assert((sna->flags & SNA_IS_HOSTED) == 0);
 	assert((sna->flags & SNA_TEAR_FREE) == 0);
 	assert(sna->mode.flip_active == 0);
+	assert(sna->mode.front_active);
+	assert(sna->scrn->vtSema);
 
 	if ((sna->flags & (data ? SNA_HAS_FLIP : SNA_HAS_ASYNC_FLIP)) == 0)
 		return 0;
diff --git a/src/sna/sna_dri2.c b/src/sna/sna_dri2.c
index 0b343cec..be5d8141 100644
--- a/src/sna/sna_dri2.c
+++ b/src/sna/sna_dri2.c
@@ -1560,11 +1560,13 @@ can_flip(struct sna * sna,
 	if (draw->type == DRAWABLE_PIXMAP)
 		return false;
 
-	if (!sna->scrn->vtSema) {
-		DBG(("%s: no, not attached to VT\n", __FUNCTION__));
+	if (!sna->mode.front_active) {
+		DBG(("%s: no, active CRTC\n", __FUNCTION__));
 		return false;
 	}
 
+	assert(sna->scrn->vtSema);
+
 	if ((sna->flags & (SNA_HAS_FLIP | SNA_HAS_ASYNC_FLIP)) == 0) {
 		DBG(("%s: no, pageflips disabled\n", __FUNCTION__));
 		return false;
diff --git a/src/sna/sna_present.c b/src/sna/sna_present.c
index dd4771c9..a1dfc91e 100644
--- a/src/sna/sna_present.c
+++ b/src/sna/sna_present.c
@@ -193,16 +193,13 @@ static bool
 check_flip__crtc(struct sna *sna,
 		 RRCrtcPtr crtc)
 {
-	if (!sna->scrn->vtSema) {
-		DBG(("%s: not master\n", __FUNCTION__));
-		return false;
-	}
-
 	if (!sna_crtc_is_on(crtc->devPrivate)) {
 		DBG(("%s: CRTC off\n", __FUNCTION__));
 		return false;
 	}
 
+	assert(sna->scrn->vtSema);
+
 	if (sna->mode.shadow_active) {
 		DBG(("%s: shadow buffer active\n", __FUNCTION__));
 		return false;
@@ -415,19 +412,28 @@ sna_present_flip(RRCrtcPtr crtc,
 static void
 sna_present_unflip(ScreenPtr screen, uint64_t event_id)
 {
+	struct sna *sna = to_sna_from_screen(screen);
 	struct kgem_bo *bo;
 
 	DBG(("%s(event=%lld)\n", __FUNCTION__, (long long)event_id));
-	bo = get_flip_bo(screen->GetScreenPixmap(screen));
-	if (bo == NULL || !page_flip(screen, NULL, event_id, bo)) {
-		struct sna *sna = to_sna_from_screen(screen);
+	if (sna->mode.front_active == 0) {
 		const struct ust_msc *swap;
-		DBG(("%s: failed, trying to restore original mode\n", __FUNCTION__));
-		xf86SetDesiredModes(sna->scrn);
+
+		DBG(("%s: no CRTC active, perform no-op flip\n", __FUNCTION__));
+
+notify:
 		swap = sna_crtc_last_swap(sna_mode_first_crtc(sna));
 		present_event_notify(event_id,
 				     ust64(swap->tv_sec, swap->tv_usec),
 				     swap->msc);
+		return;
+	}
+
+	bo = get_flip_bo(screen->GetScreenPixmap(screen));
+	if (bo == NULL || !page_flip(screen, NULL, event_id, bo)) {
+		DBG(("%s: failed, trying to restore original mode\n", __FUNCTION__));
+		xf86SetDesiredModes(sna->scrn);
+		goto notify;
 	}
 }