[PATCH v2 14/21] drm/bridge: Add an ->atomic_check() hook

[Boris Brezillon]

So that bridge drivers have a way to check/reject an atomic operation.
The drm_atomic_bridge_chain_check() (which is just a wrapper around
the ->atomic_check() hook) is called in place of
drm_bridge_chain_mode_fixup() (when ->atomic_check() is not implemented,
the core falls back to ->mode_fixup(), so the behavior should stay
the same for existing bridge drivers).

Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
---
Laurent,

I haven't clarified what's allowed to be changed in
->mode_fixup()/->atomic_check() simply because I don't know what the
constraints are. Since the problem already exists with the
->mode_fixup() hook, and given the goal of this series is to support
bus_format negotation (which does not involve tweaking the display
mode), I'd prefer to delay these semantic adjustments if you're okay
with that.

Regards,

Boris

Changes in v2:
* Clarify the fact that ->atomic_check() is replacing ->mode_fixup()
---
 drivers/gpu/drm/drm_atomic_helper.c | 12 +++---
 drivers/gpu/drm/drm_bridge.c        | 62 +++++++++++++++++++++++++++++
 include/drm/drm_bridge.h            | 29 +++++++++++++-
 3 files changed, 96 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index b3f59e757b30..2a4ac69ccc93 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -445,12 +445,12 @@ mode_fixup(struct drm_atomic_state *state)
 		encoder = new_conn_state->best_encoder;
 		funcs = encoder->helper_private;
 
-		ret = drm_bridge_chain_mode_fixup(&encoder->bridge,
-					&new_crtc_state->mode,
-					&new_crtc_state->adjusted_mode);
-		if (!ret) {
-			DRM_DEBUG_ATOMIC("Bridge fixup failed\n");
-			return -EINVAL;
+		ret = drm_atomic_bridge_chain_check(&encoder->bridge,
+						    new_crtc_state,
+						    new_conn_state);
+		if (ret) {
+			DRM_DEBUG_ATOMIC("Bridge atomic check failed\n");
+			return ret;
 		}
 
 		if (funcs && funcs->atomic_check) {
diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 5c83cac7975e..7f7e0ea5b06c 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -581,6 +581,68 @@ void drm_atomic_bridge_chain_enable(struct drm_bridge *bridge,
 }
 EXPORT_SYMBOL(drm_atomic_bridge_chain_enable);
 
+static int drm_atomic_bridge_check(struct drm_bridge *bridge,
+				   struct drm_crtc_state *crtc_state,
+				   struct drm_connector_state *conn_state)
+{
+	if (bridge->funcs->atomic_check) {
+		struct drm_bridge_state *bridge_state;
+		int ret;
+
+		bridge_state = drm_atomic_get_new_bridge_state(crtc_state->state,
+							       bridge);
+		if (WARN_ON(!bridge_state))
+			return -EINVAL;
+
+		ret = bridge->funcs->atomic_check(bridge, bridge_state,
+						  crtc_state, conn_state);
+		if (ret)
+			return ret;
+	} else if (bridge->funcs->mode_fixup) {
+		if (!bridge->funcs->mode_fixup(bridge, &crtc_state->mode,
+					       &crtc_state->adjusted_mode))
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * drm_atomic_bridge_chain_check() - Do an atomic check on the bridge chain
+ * @bridge: bridge control structure
+ * @crtc_state: new CRTC state
+ * @conn_state: new connector state
+ *
+ * Calls &drm_bridge_funcs.atomic_check() (falls back on
+ * &drm_bridge_funcs.mode_fixup()) op for all the bridges in the encoder chain,
+ * starting from the last bridge to the first. These are called before calling
+ * &drm_encoder_helper_funcs.atomic_check()
+ *
+ * RETURNS:
+ * 0 on success, a negative error code on failure
+ */
+int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
+				  struct drm_crtc_state *crtc_state,
+				  struct drm_connector_state *conn_state)
+{
+	struct drm_encoder *encoder = bridge->encoder;
+	struct drm_bridge *iter;
+
+	list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) {
+		int ret;
+
+		ret = drm_atomic_bridge_check(iter, crtc_state, conn_state);
+		if (ret)
+			return ret;
+
+		if (iter == bridge)
+			break;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_atomic_bridge_chain_check);
+
 /**
  * drm_atomic_helper_bridge_destroy_state() - Default destroy state helper
  * @bridge: the bridge this state refers to
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 231f62cd681d..7fdce6dc5f26 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -126,7 +126,9 @@ struct drm_bridge_funcs {
 	 * this function passes all other callbacks must succeed for this
 	 * configuration.
 	 *
-	 * The mode_fixup callback is optional.
+	 * The mode_fixup callback is optional. &drm_bridge_funcs.mode_fixup()
+	 * is not called when &drm_bridge_funcs.atomic_check() is implemented,
+	 * so only one of them should be provided.
 	 *
 	 * NOTE:
 	 *
@@ -389,6 +391,28 @@ struct drm_bridge_funcs {
 	void (*atomic_destroy_state)(struct drm_bridge *bridge,
 				     struct drm_bridge_state *state);
 
+	/**
+	 * @atomic_check:
+	 *
+	 * This method is responsible for checking bridge state correctness.
+	 * It can also check the state of the surrounding components in chain
+	 * to make sure the whole pipeline can work properly.
+	 *
+	 * &drm_bridge_funcs.atomic_check() hooks are called in reverse
+	 * order (from the last to the first bridge).
+	 *
+	 * This method is optional. &drm_bridge_funcs.mode_fixup() is not
+	 * called when &drm_bridge_funcs.atomic_check() is implemented, so only
+	 * one of them should be provided.
+	 *
+	 * RETURNS:
+	 * zero if the check passed, a negative error code otherwise.
+	 */
+	int (*atomic_check)(struct drm_bridge *bridge,
+			    struct drm_bridge_state *bridge_state,
+			    struct drm_crtc_state *crtc_state,
+			    struct drm_connector_state *conn_state);
+
 	/**
 	 * @atomic_reset:
 	 *
@@ -511,6 +535,9 @@ void drm_bridge_chain_mode_set(struct drm_bridge *bridge,
 void drm_bridge_chain_pre_enable(struct drm_bridge *bridge);
 void drm_bridge_chain_enable(struct drm_bridge *bridge);
 
+int drm_atomic_bridge_chain_check(struct drm_bridge *bridge,
+				  struct drm_crtc_state *crtc_state,
+				  struct drm_connector_state *conn_state);
 void drm_atomic_bridge_chain_disable(struct drm_bridge *bridge,
 				     struct drm_atomic_state *state);
 void drm_atomic_bridge_chain_post_disable(struct drm_bridge *bridge,
-- 
2.21.0