[PATCH 2/6] drm/atomic: prepare to check that drivers follow restrictions for needs_modeset

[Dmitry Baryshkov]

Some drivers might fail to follow the restrictions documented for
drm_atomic_helper_check_modesets(). In order to catch such an issues,
add the drm_atomic_state->dirty_needs_modeset field and check it in
drm_atomic_check_only(). Make sure that neither of atomic_check()
callbacks can set that field without calling
drm_atomic_helper_check_modesets() again.

Suggested-by: Simona Vetter <simona.vetter@xxxxxxxx>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
---
 drivers/gpu/drm/drm_atomic.c        |  3 ++
 drivers/gpu/drm/drm_atomic_helper.c | 77 +++++++++++++++++++++++++++++++++----
 include/drm/drm_atomic.h            | 10 +++++
 3 files changed, 82 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 9ea2611770f43ce7ccba410406d5f2c528aab022..202e4e64bd31921d0a4d4b86605b501311e14c33 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -1449,6 +1449,9 @@ int drm_atomic_check_only(struct drm_atomic_state *state)
 		}
 	}
 
+	WARN_RATELIMIT(state->dirty_needs_modeset,
+		       "Driver changed needs_modeset under drm_atomic_helper_check_modeset()");
+
 	if (!state->allow_modeset) {
 		for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
 			if (drm_atomic_crtc_needs_modeset(new_crtc_state)) {
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index f26887c3fe8b194137200f9f2426653274c50fda..2c62840416f4b807d6a880b5c30ae024a16af528 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -433,6 +433,7 @@ mode_fixup(struct drm_atomic_state *state)
 
 	for_each_new_connector_in_state(state, connector, new_conn_state, i) {
 		const struct drm_encoder_helper_funcs *funcs;
+		bool old_needs_modeset = false;
 		struct drm_encoder *encoder;
 		struct drm_bridge *bridge;
 
@@ -451,6 +452,9 @@ mode_fixup(struct drm_atomic_state *state)
 		encoder = new_conn_state->best_encoder;
 		funcs = encoder->helper_private;
 
+		if (new_crtc_state)
+			old_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
+
 		bridge = drm_bridge_chain_get_first_bridge(encoder);
 		ret = drm_atomic_bridge_chain_check(bridge,
 						    new_crtc_state,
@@ -479,6 +483,12 @@ mode_fixup(struct drm_atomic_state *state)
 				return -EINVAL;
 			}
 		}
+
+		if (new_crtc_state) {
+			bool new_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
+
+			state->dirty_needs_modeset |= (new_needs_modeset != old_needs_modeset);
+		}
 	}
 
 	for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
@@ -574,6 +584,36 @@ mode_valid(struct drm_atomic_state *state)
 	return 0;
 }
 
+static int
+connector_atomic_check(struct drm_atomic_state *state,
+		       struct drm_connector *connector,
+		       struct drm_connector_state *old_connector_state,
+		       struct drm_connector_state *new_connector_state)
+{
+	const struct drm_connector_helper_funcs *funcs = connector->helper_private;
+	struct drm_crtc_state *new_crtc_state;
+	bool old_needs_modeset = false;
+	int ret;
+
+	if (new_connector_state->crtc)
+		new_crtc_state = drm_atomic_get_new_crtc_state(state, new_connector_state->crtc);
+	if (new_crtc_state)
+		old_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
+
+	if (funcs->atomic_check)
+		ret = funcs->atomic_check(connector, state);
+	else
+		ret = 0;
+
+	if (new_crtc_state) {
+		bool new_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
+
+		state->dirty_needs_modeset |= (new_needs_modeset != old_needs_modeset);
+	}
+
+	return ret;
+}
+
 /**
  * drm_atomic_helper_check_modeset - validate state object for modeset changes
  * @dev: DRM device
@@ -628,6 +668,8 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 	int i, ret;
 	unsigned int connectors_mask = 0, user_connectors_mask = 0;
 
+	state->dirty_needs_modeset = false;
+
 	for_each_oldnew_connector_in_state(state, connector, old_connector_state, new_connector_state, i)
 		user_connectors_mask |= BIT(i);
 
@@ -683,8 +725,6 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 		return ret;
 
 	for_each_oldnew_connector_in_state(state, connector, old_connector_state, new_connector_state, i) {
-		const struct drm_connector_helper_funcs *funcs = connector->helper_private;
-
 		WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
 
 		/*
@@ -710,8 +750,8 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 				new_crtc_state->connectors_changed = true;
 		}
 
-		if (funcs->atomic_check)
-			ret = funcs->atomic_check(connector, state);
+		ret = connector_atomic_check(state, connector,
+					     old_connector_state, new_connector_state);
 		if (ret) {
 			drm_dbg_atomic(dev,
 				       "[CONNECTOR:%d:%s] driver check failed\n",
@@ -752,13 +792,11 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 	 * has been called on them when a modeset is forced.
 	 */
 	for_each_oldnew_connector_in_state(state, connector, old_connector_state, new_connector_state, i) {
-		const struct drm_connector_helper_funcs *funcs = connector->helper_private;
-
 		if (connectors_mask & BIT(i))
 			continue;
 
-		if (funcs->atomic_check)
-			ret = funcs->atomic_check(connector, state);
+		ret = connector_atomic_check(state, connector,
+					     old_connector_state, new_connector_state);
 		if (ret) {
 			drm_dbg_atomic(dev,
 				       "[CONNECTOR:%d:%s] driver check failed\n",
@@ -994,6 +1032,7 @@ drm_atomic_helper_check_planes(struct drm_device *dev,
 
 	for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) {
 		const struct drm_plane_helper_funcs *funcs;
+		bool old_needs_modeset = false;
 
 		WARN_ON(!drm_modeset_is_locked(&plane->mutex));
 
@@ -1006,6 +1045,12 @@ drm_atomic_helper_check_planes(struct drm_device *dev,
 		if (!funcs || !funcs->atomic_check)
 			continue;
 
+		if (new_plane_state->crtc)
+			new_crtc_state = drm_atomic_get_new_crtc_state(state,
+								       new_plane_state->crtc);
+		if (new_crtc_state)
+			old_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
+
 		ret = funcs->atomic_check(plane, state);
 		if (ret) {
 			drm_dbg_atomic(plane->dev,
@@ -1013,16 +1058,26 @@ drm_atomic_helper_check_planes(struct drm_device *dev,
 				       plane->base.id, plane->name);
 			return ret;
 		}
+
+		if (new_crtc_state) {
+			bool new_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
+
+			state->dirty_needs_modeset |= (new_needs_modeset != old_needs_modeset);
+		}
 	}
 
 	for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
 		const struct drm_crtc_helper_funcs *funcs;
+		bool old_needs_modeset = false;
 
 		funcs = crtc->helper_private;
 
 		if (!funcs || !funcs->atomic_check)
 			continue;
 
+		if (new_crtc_state)
+			old_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
+
 		ret = funcs->atomic_check(crtc, state);
 		if (ret) {
 			drm_dbg_atomic(crtc->dev,
@@ -1030,6 +1085,12 @@ drm_atomic_helper_check_planes(struct drm_device *dev,
 				       crtc->base.id, crtc->name);
 			return ret;
 		}
+
+		if (new_crtc_state) {
+			bool new_needs_modeset = drm_atomic_crtc_needs_modeset(new_crtc_state);
+
+			state->dirty_needs_modeset |= (new_needs_modeset != old_needs_modeset);
+		}
 	}
 
 	return ret;
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
index 31ca88deb10d262fb3a3f8e14d2afe24f8410cb1..7b0dbd3c8a3df340399a458aaf79263f0fdc24e5 100644
--- a/include/drm/drm_atomic.h
+++ b/include/drm/drm_atomic.h
@@ -408,6 +408,16 @@ struct drm_atomic_state {
 	 */
 	bool duplicated : 1;
 
+	/**
+	 * @dirty_needs_modeset:
+	 *
+	 * Indicates whether the drm_atomic_crtc_needs_modeset() changed in an
+	 * unexpected way. Usually this means that driver implements atomic
+	 * helpers using drm_atomic_crtc_needs_modeset(), but mode_changed has
+	 * toggled by one of its atomic_check() callbacks.
+	 */
+	bool dirty_needs_modeset : 1;
+
 	/**
 	 * @planes:
 	 *

-- 
2.39.5