drm/i915: Fix current fb blocking for page flip

Block execbuffer for the fb to be flipped away, not the one that is to
be flipped in.

[ickle: rewritten for -next]
Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: Kristian Høgsberg <krh@bitplanet.net>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 8 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index e031d82381e5..990f065374b2 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -4991,9 +4991,7 @@ static void do_intel_finish_page_flip(struct drm_device *dev,
 
         spin_unlock_irqrestore(&dev->event_lock, flags);
 
-        obj_priv = to_intel_bo(work->pending_flip_obj);
-
-        /* Initial scanout buffer will have a 0 pending flip count */
+        obj_priv = to_intel_bo(work->old_fb_obj);
         atomic_clear_mask(1 << intel_crtc->plane,
                           &obj_priv->pending_flip.counter);
         if (atomic_read(&obj_priv->pending_flip) == 0)
@@ -5092,9 +5090,14 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
         if (ret)
                 goto cleanup_objs;
 
-        obj_priv = to_intel_bo(obj);
-        atomic_add(1 << intel_crtc->plane, &obj_priv->pending_flip);
+        /* Block clients from rendering to the new back buffer until
+         * the flip occurs and the object is no longer visible.
+         */
+        atomic_add(1 << intel_crtc->plane,
+                   &to_intel_bo(work->old_fb_obj)->pending_flip);
+
         work->pending_flip_obj = obj;
+        obj_priv = to_intel_bo(obj);
 
         if (IS_GEN3(dev) || IS_GEN2(dev)) {
                 u32 flip_mask;