[PATCH 1/2] drm/atomic: track bitmask of planes attached to crtc

[Rob Clark <robdclark@gmail.com>]

Chasing plane->state->crtc of planes that are *not* part of the same
atomic update is racy, making it incredibly awkward (or impossible) to
do something simple like iterate over all planes and figure out which
ones are attached to a crtc.

Solve this by adding a bitmask of currently attached planes in the
crtc-state.

Note that the transitional helpers do not maintain the plane_mask.  But
they only support the legacy ioctls, which have sufficient brute-force
locking around plane updates that they can continue to loop over all
planes to see what is attached to a crtc the old way.

Signed-off-by: Rob Clark <robdclark@gmail.com>
---
 drivers/gpu/drm/drm_atomic.c        | 25 ++++++++++++++++++++-----
 drivers/gpu/drm/drm_atomic_helper.c |  8 ++++----
 include/drm/drm_atomic.h            |  4 ++--
 include/drm/drm_crtc.h              | 14 +++++++++++---
 4 files changed, 37 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index d3b4674..8effbba 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -350,7 +350,8 @@ EXPORT_SYMBOL(drm_atomic_get_connector_state);
 
 /**
  * drm_atomic_set_crtc_for_plane - set crtc for plane
- * @plane_state: atomic state object for the plane
+ * @state: the incoming atomic state
+ * @plane: the plane whose incoming state to update
  * @crtc: crtc to use for the plane
  *
  * Changing the assigned crtc for a plane requires us to grab the lock and state
@@ -363,20 +364,34 @@ EXPORT_SYMBOL(drm_atomic_get_connector_state);
  * sequence must be restarted. All other errors are fatal.
  */
 int
-drm_atomic_set_crtc_for_plane(struct drm_plane_state *plane_state,
-			      struct drm_crtc *crtc)
+drm_atomic_set_crtc_for_plane(struct drm_atomic_state *state,
+			      struct drm_plane *plane, struct drm_crtc *crtc)
 {
+	struct drm_plane_state *plane_state =
+			drm_atomic_get_plane_state(state, plane);
 	struct drm_crtc_state *crtc_state;
 
-	if (crtc) {
+	/* acquire outgoing crtc lock, and clear bit in outgoing crtc mask: */
+	if (plane_state->crtc) {
 		crtc_state = drm_atomic_get_crtc_state(plane_state->state,
-						       crtc);
+						       plane_state->crtc);
 		if (IS_ERR(crtc_state))
 			return PTR_ERR(crtc_state);
+
+		crtc_state->plane_mask &= ~(1 << drm_plane_index(plane));
 	}
 
 	plane_state->crtc = crtc;
 
+	/* acquire incoming crtc lock, and set bit in incoming crtc mask: */
+	if (crtc) {
+		crtc_state = drm_atomic_get_crtc_state(plane_state->state,
+						       crtc);
+		if (IS_ERR(crtc_state))
+			return PTR_ERR(crtc_state);
+		crtc_state->plane_mask |= (1 << drm_plane_index(plane));
+	}
+
 	if (crtc)
 		DRM_DEBUG_KMS("Link plane state %p to [CRTC:%d]\n",
 			      plane_state, crtc->base.id);
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index a17b8e9..d765d37 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1187,7 +1187,7 @@ retry:
 		goto fail;
 	}
 
-	ret = drm_atomic_set_crtc_for_plane(plane_state, crtc);
+	ret = drm_atomic_set_crtc_for_plane(state, plane, crtc);
 	if (ret != 0)
 		goto fail;
 	drm_atomic_set_fb_for_plane(plane_state, fb);
@@ -1255,7 +1255,7 @@ retry:
 		goto fail;
 	}
 
-	ret = drm_atomic_set_crtc_for_plane(plane_state, NULL);
+	ret = drm_atomic_set_crtc_for_plane(state, plane, NULL);
 	if (ret != 0)
 		goto fail;
 	drm_atomic_set_fb_for_plane(plane_state, NULL);
@@ -1426,7 +1426,7 @@ retry:
 		goto fail;
 	}
 
-	ret = drm_atomic_set_crtc_for_plane(primary_state, crtc);
+	ret = drm_atomic_set_crtc_for_plane(state, crtc->primary, crtc);
 	if (ret != 0)
 		goto fail;
 	drm_atomic_set_fb_for_plane(primary_state, set->fb);
@@ -1698,7 +1698,7 @@ retry:
 		goto fail;
 	}
 
-	ret = drm_atomic_set_crtc_for_plane(plane_state, crtc);
+	ret = drm_atomic_set_crtc_for_plane(state, plane, crtc);
 	if (ret != 0)
 		goto fail;
 	drm_atomic_set_fb_for_plane(plane_state, fb);
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index 9d91916..6ff8775 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -44,8 +44,8 @@ drm_atomic_get_connector_state(struct drm_atomic_state *state,
 			       struct drm_connector *connector);
 
 int __must_check
-drm_atomic_set_crtc_for_plane(struct drm_plane_state *plane_state,
-			      struct drm_crtc *crtc);
+drm_atomic_set_crtc_for_plane(struct drm_atomic_state *state,
+			      struct drm_plane *plane, struct drm_crtc *crtc);
 void drm_atomic_set_fb_for_plane(struct drm_plane_state *plane_state,
 				 struct drm_framebuffer *fb);
 int __must_check
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index b459e8f..4cf6905 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -231,6 +231,7 @@ struct drm_atomic_state;
  * struct drm_crtc_state - mutable CRTC state
  * @enable: whether the CRTC should be enabled, gates all other state
  * @mode_changed: for use by helpers and drivers when computing state updates
+ * @plane_mask: bitmask of (1 << drm_plane_index(plane)) of attached planes
  * @last_vblank_count: for helpers and drivers to capture the vblank of the
  * 	update to ensure framebuffer cleanup isn't done too early
  * @planes_changed: for use by helpers and drivers when computing state updates
@@ -247,6 +248,13 @@ struct drm_crtc_state {
 	bool planes_changed : 1;
 	bool mode_changed : 1;
 
+	/* attached planes bitmask:
+	 * WARNING: transitional helpers do not maintain plane_mask so
+	 * drivers not converted over to atomic helpers should not rely
+	 * on plane_mask being accurate!
+	 */
+	u32 plane_mask;
+
 	/* last_vblank_count: for vblank waits before cleanup */
 	u32 last_vblank_count;
 
@@ -438,7 +446,7 @@ struct drm_crtc {
  * @state: backpointer to global drm_atomic_state
  */
 struct drm_connector_state {
-	struct drm_crtc *crtc;
+	struct drm_crtc *crtc;  /* do not write directly, use drm_atomic_set_crtc_for_connector() */
 
 	struct drm_encoder *best_encoder;
 
@@ -673,8 +681,8 @@ struct drm_connector {
  * @state: backpointer to global drm_atomic_state
  */
 struct drm_plane_state {
-	struct drm_crtc *crtc;
-	struct drm_framebuffer *fb;
+	struct drm_crtc *crtc;   /* do not write directly, use drm_atomic_set_crtc_for_plane() */
+	struct drm_framebuffer *fb;  /* do not write directly, use drm_atomic_set_fb_for_plane() */
 	struct fence *fence;
 
 	/* Signed dest location allows it to be partially off screen */
-- 
1.9.3

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