3 files changed, 34 insertions, 8 deletions

diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
index 7f08d681a74b..82f914af4156 100644
--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -669,6 +669,14 @@ void vc4_disable_vblank(struct drm_device *dev, unsigned int crtc_id)
         CRTC_WRITE(PV_INTEN, 0);
 }
 
+/* Must be called with the event lock held */
+bool vc4_event_pending(struct drm_crtc *crtc)
+{
+        struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
+
+        return !!vc4_crtc->event;
+}
+
 static void vc4_crtc_handle_page_flip(struct vc4_crtc *vc4_crtc)
 {
         struct drm_crtc *crtc = &vc4_crtc->base;
diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
index fef172804345..b3064e2e79c1 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.h
+++ b/drivers/gpu/drm/vc4/vc4_drv.h
@@ -442,6 +442,7 @@ int vc4_bo_stats_debugfs(struct seq_file *m, void *arg);
 extern struct platform_driver vc4_crtc_driver;
 int vc4_enable_vblank(struct drm_device *dev, unsigned int crtc_id);
 void vc4_disable_vblank(struct drm_device *dev, unsigned int crtc_id);
+bool vc4_event_pending(struct drm_crtc *crtc);
 int vc4_crtc_debugfs_regs(struct seq_file *m, void *arg);
 int vc4_crtc_get_scanoutpos(struct drm_device *dev, unsigned int crtc_id,
                             unsigned int flags, int *vpos, int *hpos,
diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
index c1f65c6c8e60..67af2af70af0 100644
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -119,17 +119,34 @@ static int vc4_atomic_commit(struct drm_device *dev,
 
         /* Make sure that any outstanding modesets have finished. */
         if (nonblock) {
-                ret = down_trylock(&vc4->async_modeset);
-                if (ret) {
+                struct drm_crtc *crtc;
+                struct drm_crtc_state *crtc_state;
+                unsigned long flags;
+                bool busy = false;
+
+                /*
+                 * If there's an undispatched event to send then we're
+                 * obviously still busy.  If there isn't, then we can
+                 * unconditionally wait for the semaphore because it
+                 * shouldn't be contended (for long).
+                 *
+                 * This is to prevent a race where queuing a new flip
+                 * from userspace immediately on receipt of an event
+                 * beats our clean-up and returns EBUSY.
+                 */
+                spin_lock_irqsave(&dev->event_lock, flags);
+                for_each_crtc_in_state(state, crtc, crtc_state, i)
+                        busy |= vc4_event_pending(crtc);
+                spin_unlock_irqrestore(&dev->event_lock, flags);
+                if (busy) {
                         kfree(c);
                         return -EBUSY;
                 }
-        } else {
-                ret = down_interruptible(&vc4->async_modeset);
-                if (ret) {
-                        kfree(c);
-                        return ret;
-                }
+        }
+        ret = down_interruptible(&vc4->async_modeset);
+        if (ret) {
+                kfree(c);
+                return ret;
         }
 
         ret = drm_atomic_helper_prepare_planes(dev, state);