[RFC PATCH 5/5] drm/atomic: Make async plane update checks work as intended.

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

By always keeping track of the last commit in plane_state, we know
whether there is an active update on the plane or not. With that
information we can reject the fast update, and force the slowpath
to be used as was originally intended.

Cc: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
---
 drivers/gpu/drm/drm_atomic_helper.c  | 25 +++++++++++--------------
 drivers/gpu/drm/i915/intel_display.c |  8 ++++++++
 include/drm/drm_plane.h              |  5 +++--
 3 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 034f563fb130..384d99347bb3 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1388,8 +1388,8 @@ int drm_atomic_helper_async_check(struct drm_device *dev,
 {
 	struct drm_crtc *crtc;
 	struct drm_crtc_state *crtc_state;
-	struct drm_plane *__plane, *plane = NULL;
-	struct drm_plane_state *__plane_state, *plane_state = NULL;
+	struct drm_plane *plane;
+	struct drm_plane_state *old_plane_state, *new_plane_state;
 	const struct drm_plane_helper_funcs *funcs;
 	int i, n_planes = 0;
 
@@ -1398,33 +1398,33 @@ int drm_atomic_helper_async_check(struct drm_device *dev,
 			return -EINVAL;
 	}
 
-	for_each_new_plane_in_state(state, __plane, __plane_state, i) {
+	for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i)
 		n_planes++;
-		plane = __plane;
-		plane_state = __plane_state;
-	}
 
 	/* FIXME: we support only single plane updates for now */
-	if (!plane || n_planes != 1)
+	if (n_planes != 1)
 		return -EINVAL;
 
-	if (!plane_state->crtc)
+	if (!new_plane_state->crtc)
 		return -EINVAL;
 
 	funcs = plane->helper_private;
 	if (!funcs->atomic_async_update)
 		return -EINVAL;
 
-	if (plane_state->fence)
+	if (new_plane_state->fence)
 		return -EINVAL;
 
 	/*
-	 * TODO: Don't do an async update if there is an outstanding commit modifying
+	 * Don't do an async update if there is an outstanding commit modifying
 	 * the plane.  This prevents our async update's changes from getting
 	 * overridden by a previous synchronous update's state.
 	 */
+	if (old_plane_state->commit &&
+	    !try_wait_for_completion(&old_plane_state->commit->hw_done))
+		return -EBUSY;
 
-	return funcs->atomic_async_check(plane, plane_state);
+	return funcs->atomic_async_check(plane, new_plane_state);
 }
 EXPORT_SYMBOL(drm_atomic_helper_async_check);
 
@@ -1790,9 +1790,6 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
 	}
 
 	for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) {
-		if (new_plane_state->crtc)
-			continue;
-
 		if (nonblock && old_plane_state->commit &&
 		    !try_wait_for_completion(&old_plane_state->commit->flip_done))
 			return -EBUSY;
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 70ce02753177..cf21ec4ce920 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13043,6 +13043,14 @@ intel_legacy_cursor_update(struct drm_plane *plane,
 		goto slow;
 
 	old_plane_state = plane->state;
+	/*
+	 * Don't do an async update if there is an outstanding commit modifying
+	 * the plane.  This prevents our async update's changes from getting
+	 * overridden by a previous synchronous update's state.
+	 */
+	if (old_plane_state->commit &&
+	    !try_wait_for_completion(&old_plane_state->commit->hw_done))
+		goto slow;
 
 	/*
 	 * If any parameters change that may affect watermarks,
diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index 7d96116fd4c4..feb9941d0cdb 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -124,9 +124,10 @@ struct drm_plane_state {
 	bool visible;
 
 	/**
-	 * @commit: Tracks the pending commit to prevent use-after-free conditions.
+	 * @commit: Tracks the pending commit to prevent use-after-free conditions,
+	 * and for async plane updates.
 	 *
-	 * Is only set when @crtc is NULL.
+	 * May be NULL.
 	 */
 	struct drm_crtc_commit *commit;
 
-- 
2.11.0

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