drm: make drm_file use keyed wakeups

Some processes, such as systemd, are only polling for EPOLLERR|EPOLLHUP.
As drm_file uses unkeyed wakeups, such a poll receives many spurious
wakeups from uninteresting events.

Use keyed wakeups to allow the wakeup target to more efficiently discard
these uninteresting events.
Signed-off-by: Kenny Levinsen <kl@kl.wtf>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200424145103.3048-1-kl@kl.wtf

drivers/gpu/drm/drm_file.c

@@ -613,7 +613,8 @@ ssize_t drm_read(struct file *filp, char __user *buffer,
 				file_priv->event_space -= length;
 				list_add(&e->link, &file_priv->event_list);
 				spin_unlock_irq(&dev->event_lock);
-				wake_up_interruptible(&file_priv->event_wait);
+				wake_up_interruptible_poll(&file_priv->event_wait,
+					EPOLLIN | EPOLLRDNORM);
 				break;
 			}
 
@@ -809,7 +810,8 @@ void drm_send_event_locked(struct drm_device *dev, struct drm_pending_event *e)
 	list_del(&e->pending_link);
 	list_add_tail(&e->link,
 		      &e->file_priv->event_list);
-	wake_up_interruptible(&e->file_priv->event_wait);
+	wake_up_interruptible_poll(&e->file_priv->event_wait,
+		EPOLLIN | EPOLLRDNORM);
 }
 EXPORT_SYMBOL(drm_send_event_locked);