[PATCH v2 2/2] drm/fence: allow fence waiting to be interrupted by userspace

[Gustavo Padovan]

From: Gustavo Padovan <gustavo.padovan at collabora.co.uk>

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

Signed-off-by: Gustavo Padovan <gustavo.padovan at collabora.co.uk>
---
 drivers/gpu/drm/drm_atomic_helper.c | 33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index bf1bc43..292d15b 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1022,20 +1022,37 @@ int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
 {
 	struct drm_plane *plane;
 	struct drm_plane_state *plane_state;
+	struct fence *fence;
 	int i, ret;
 
 	for_each_plane_in_state(state, plane, plane_state, i) {
-		if (!plane->state->fence)
+		if (!plane->state->fence && !plane_state->fence)
 			continue;
 
-		WARN_ON(!plane->state->fb);
+		/*
+		 * If the caller asks for an interruptible wait it means
+		 * that the state were not swapped yet and the operation
+		 * can still be interrupted by userspace, so we need
+		 * to look to plane_state instead.
+		 */
+		if (intr) {
+			fence = plane_state->fence;
+			WARN_ON(!plane_state->fb);
+		} else {
+			fence = plane->state->fence;
+			WARN_ON(!plane->state->fb);
+		}
 
-		ret = fence_wait(plane->state->fence, intr);
+		ret = fence_wait(fence, intr);
 		if (ret)
 			return ret;
 
-		fence_put(plane->state->fence);
-		plane->state->fence = NULL;
+		fence_put(fence);
+
+		if (intr)
+			plane_state->fence = NULL;
+		else
+			plane->state->fence = NULL;
 	}
 
 	return 0;
@@ -1244,6 +1261,12 @@ 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
-- 
2.5.5