4 files changed, 41 insertions, 11 deletions

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 8afc0dd7de6..e6a11ca85ea 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -317,7 +317,7 @@ static int i915_gem_pageflip_info(struct seq_file *m, void *data)
                         seq_printf(m, "No flip due on pipe %c (plane %c)\n",
                                    pipe, plane);
                 } else {
-                        if (!work->pending) {
+                        if (atomic_read(&work->pending) < INTEL_FLIP_COMPLETE) {
                                 seq_printf(m, "Flip queued on pipe %c (plane %c)\n",
                                            pipe, plane);
                         } else {
@@ -328,7 +328,7 @@ static int i915_gem_pageflip_info(struct seq_file *m, void *data)
                                 seq_printf(m, "Stall check enabled, ");
                         else
                                 seq_printf(m, "Stall check waiting for page flip ioctl, ");
-                        seq_printf(m, "%d prepares\n", work->pending);
+                        seq_printf(m, "%d prepares\n", atomic_read(&work->pending));
 
                         if (work->old_fb_obj) {
                                 struct drm_i915_gem_object *obj = work->old_fb_obj;
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 6cd3dc94b47..a4dc97f8b9f 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1466,7 +1466,9 @@ static void i915_pageflip_stall_check(struct drm_device *dev, int pipe)
         spin_lock_irqsave(&dev->event_lock, flags);
         work = intel_crtc->unpin_work;
 
-        if (work == NULL || work->pending || !work->enable_stall_check) {
+        if (work == NULL ||
+            atomic_read(&work->pending) >= INTEL_FLIP_COMPLETE ||
+            !work->enable_stall_check) {
                 /* Either the pending flip IRQ arrived, or we're too early. Don't check */
                 spin_unlock_irqrestore(&dev->event_lock, flags);
                 return;
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 78d12c47147..f8ee3d16109 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6929,11 +6929,18 @@ static void do_intel_finish_page_flip(struct drm_device *dev,
 
         spin_lock_irqsave(&dev->event_lock, flags);
         work = intel_crtc->unpin_work;
-        if (work == NULL || !work->pending) {
+
+        /* Ensure we don't miss a work->pending update ... */
+        smp_rmb();
+
+        if (work == NULL || atomic_read(&work->pending) < INTEL_FLIP_COMPLETE) {
                 spin_unlock_irqrestore(&dev->event_lock, flags);
                 return;
         }
 
+        /* and that the unpin work is consistent wrt ->pending. */
+        smp_rmb();
+
         intel_crtc->unpin_work = NULL;
 
         if (work->event)
@@ -6977,16 +6984,25 @@ void intel_prepare_page_flip(struct drm_device *dev, int plane)
                 to_intel_crtc(dev_priv->plane_to_crtc_mapping[plane]);
         unsigned long flags;
 
+        /* NB: An MMIO update of the plane base pointer will also
+         * generate a page-flip completion irq, i.e. every modeset
+         * is also accompanied by a spurious intel_prepare_page_flip().
+         */
         spin_lock_irqsave(&dev->event_lock, flags);
-        if (intel_crtc->unpin_work) {
-                if ((++intel_crtc->unpin_work->pending) > 1)
-                        DRM_ERROR("Prepared flip multiple times\n");
-        } else {
-                DRM_DEBUG_DRIVER("preparing flip with no unpin work?\n");
-        }
+        if (intel_crtc->unpin_work)
+                atomic_inc_not_zero(&intel_crtc->unpin_work->pending);
         spin_unlock_irqrestore(&dev->event_lock, flags);
 }
 
+inline static void intel_mark_page_flip_active(struct intel_crtc *intel_crtc)
+{
+        /* Ensure that the work item is consistent when activating it ... */
+        smp_wmb();
+        atomic_set(&intel_crtc->unpin_work->pending, INTEL_FLIP_PENDING);
+        /* and that it is marked active as soon as the irq could fire. */
+        smp_wmb();
+}
+
 static int intel_gen2_queue_flip(struct drm_device *dev,
                                  struct drm_crtc *crtc,
                                  struct drm_framebuffer *fb,
@@ -7020,6 +7036,8 @@ static int intel_gen2_queue_flip(struct drm_device *dev,
         intel_ring_emit(ring, fb->pitches[0]);
         intel_ring_emit(ring, obj->gtt_offset + intel_crtc->dspaddr_offset);
         intel_ring_emit(ring, 0); /* aux display base address, unused */
+
+        intel_mark_page_flip_active(intel_crtc);
         intel_ring_advance(ring);
         return 0;
 
@@ -7060,6 +7078,7 @@ static int intel_gen3_queue_flip(struct drm_device *dev,
         intel_ring_emit(ring, obj->gtt_offset + intel_crtc->dspaddr_offset);
         intel_ring_emit(ring, MI_NOOP);
 
+        intel_mark_page_flip_active(intel_crtc);
         intel_ring_advance(ring);
         return 0;
 
@@ -7106,6 +7125,8 @@ static int intel_gen4_queue_flip(struct drm_device *dev,
         pf = 0;
         pipesrc = I915_READ(PIPESRC(intel_crtc->pipe)) & 0x0fff0fff;
         intel_ring_emit(ring, pf | pipesrc);
+
+        intel_mark_page_flip_active(intel_crtc);
         intel_ring_advance(ring);
         return 0;
 
@@ -7148,6 +7169,8 @@ static int intel_gen6_queue_flip(struct drm_device *dev,
         pf = 0;
         pipesrc = I915_READ(PIPESRC(intel_crtc->pipe)) & 0x0fff0fff;
         intel_ring_emit(ring, pf | pipesrc);
+
+        intel_mark_page_flip_active(intel_crtc);
         intel_ring_advance(ring);
         return 0;
 
@@ -7202,6 +7225,8 @@ static int intel_gen7_queue_flip(struct drm_device *dev,
         intel_ring_emit(ring, (fb->pitches[0] | obj->tiling_mode));
         intel_ring_emit(ring, obj->gtt_offset + intel_crtc->dspaddr_offset);
         intel_ring_emit(ring, (MI_NOOP));
+
+        intel_mark_page_flip_active(intel_crtc);
         intel_ring_advance(ring);
         return 0;
 
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 522061ca068..3915ca9abd4 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -401,7 +401,10 @@ struct intel_unpin_work {
         struct drm_i915_gem_object *old_fb_obj;
         struct drm_i915_gem_object *pending_flip_obj;
         struct drm_pending_vblank_event *event;
-        int pending;
+        atomic_t pending;
+#define INTEL_FLIP_INACTIVE     0
+#define INTEL_FLIP_PENDING      1
+#define INTEL_FLIP_COMPLETE     2
         bool enable_stall_check;
 };