drm/fence: allow fence waiting to be interrupted by userspace

If userspace is running an synchronously atomic commit and interrupts the
atomic operation during fence_wait() it will hang until the timer expires,
so here we change the wait to be interruptible so it stop immediately when
userspace wants to quit.

Also adds the necessary error checking for fence_wait().

v2: Comment by Daniel Vetter
	- Add error checking for fence_wait()

v3: Rebase on top of new atomic noblocking support

v4: Comment by Maarten Lankhorst
	- remove 'swapped' bitfield as it was duplicating information

v5: Comments by Maarten Lankhorst
	- assign plane->state to plane_state if !intr
	- squash previous patch into this one

v6: Comment by Sean Paul
	- rename intr to pre_swap

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
[seanpaul fixed a couple checkpatch warnings and moved the preswap comment]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1473707291-14781-1-git-send-email-gustavo@padovan.org

drivers/gpu/drm/drm_atomic_helper.c

@@ -1009,29 +1009,46 @@ EXPORT_SYMBOL(drm_atomic_helper_commit_modeset_enables);
  * drm_atomic_helper_wait_for_fences - wait for fences stashed in plane state
  * @dev: DRM device
  * @state: atomic state object with old state structures
+ * @pre_swap: if true, do an interruptible wait
  *
  * For implicit sync, driver should fish the exclusive fence out from the
  * incoming fb's and stash it in the drm_plane_state.  This is called after
  * drm_atomic_helper_swap_state() so it uses the current plane state (and
  * just uses the atomic state to find the changed planes)
+ *
+ * Returns zero if success or < 0 if fence_wait() fails.
  */
-void drm_atomic_helper_wait_for_fences(struct drm_device *dev,
-			    struct drm_atomic_state *state)
+int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
+				      struct drm_atomic_state *state,
+				      bool pre_swap)
 {
 	struct drm_plane *plane;
 	struct drm_plane_state *plane_state;
-	int i;
+	int i, ret;
 
 	for_each_plane_in_state(state, plane, plane_state, i) {
-		if (!plane->state->fence)
+		if (!pre_swap)
+			plane_state = plane->state;
+
+		if (!plane_state->fence)
 			continue;
 
-		WARN_ON(!plane->state->fb);
+		WARN_ON(!plane_state->fb);
+
+		/*
+		 * If waiting for fences pre-swap (ie: nonblock), userspace can
+		 * still interrupt the operation. Instead of blocking until the
+		 * timer expires, make the wait interruptible.
+		 */
+		ret = fence_wait(plane_state->fence, pre_swap);
+		if (ret)
+			return ret;
 
-		fence_wait(plane->state->fence, false);
-		fence_put(plane->state->fence);
-		plane->state->fence = NULL;
+		fence_put(plane_state->fence);
+		plane_state->fence = NULL;
 	}
+
+	return 0;
 }
 EXPORT_SYMBOL(drm_atomic_helper_wait_for_fences);
 
@@ -1179,7 +1196,7 @@ static void commit_tail(struct drm_atomic_state *state)
 
 	funcs = dev->mode_config.helper_private;
 
-	drm_atomic_helper_wait_for_fences(dev, state);
+	drm_atomic_helper_wait_for_fences(dev, state, false);
 
 	drm_atomic_helper_wait_for_dependencies(state);
 
@@ -1238,6 +1255,12 @@ int drm_atomic_helper_commit(struct drm_device *dev,
 	if (ret)
 		return ret;
 
+	if (!nonblock) {
+		ret = drm_atomic_helper_wait_for_fences(dev, state, true);
+		if (ret)
+			return ret;
+	}
+
 	/*
 	 * This is the point of no return - everything below never fails except
 	 * when the hw goes bonghits. Which means we can commit the new state on

drivers/gpu/drm/msm/msm_atomic.c

@@ -112,7 +112,7 @@ static void complete_commit(struct msm_commit *c, bool async)
 	struct msm_drm_private *priv = dev->dev_private;
 	struct msm_kms *kms = priv->kms;
 
-	drm_atomic_helper_wait_for_fences(dev, state);
+	drm_atomic_helper_wait_for_fences(dev, state, false);
 
 	kms->funcs->prepare_commit(kms, state);
 

include/drm/drm_atomic_helper.h

@@ -45,8 +45,9 @@ int drm_atomic_helper_commit(struct drm_device *dev,
 			     struct drm_atomic_state *state,
 			     bool nonblock);
 
-void drm_atomic_helper_wait_for_fences(struct drm_device *dev,
-					struct drm_atomic_state *state);
+int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
+					struct drm_atomic_state *state,
+					bool pre_swap);
 bool drm_atomic_helper_framebuffer_changed(struct drm_device *dev,
 					   struct drm_atomic_state *old_state,
 					   struct drm_crtc *crtc);