drm/vc4: crtc: Rework the encoder retrieval code (again)

It turns out the encoder retrieval code, in addition to being
unnecessarily complicated, has a bug when only the planes and crtcs are
affected by a given atomic commit.

Indeed, in such a case, either drm_atomic_get_old_connector_state or
drm_atomic_get_new_connector_state will return NULL and thus our encoder
retrieval code will not match on anything.

We can however simplify the code by using drm_for_each_encoder_mask, the
drm_crtc_state storing the encoders a given CRTC is connected to
directly and without relying on any other state.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20211025152903.1088803-6-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_crtc.c

@@ -282,26 +282,14 @@ static u32 vc4_crtc_get_fifo_full_level_bits(struct vc4_crtc *vc4_crtc,
  * same CRTC.
  */
 struct drm_encoder *vc4_get_crtc_encoder(struct drm_crtc *crtc,
-					 struct drm_atomic_state *state,
-					 struct drm_connector_state *(*get_state)(struct drm_atomic_state *state,
-										  struct drm_connector *connector))
+					 struct drm_crtc_state *state)
 {
-	struct drm_connector *connector;
-	struct drm_connector_list_iter conn_iter;
-
-	drm_connector_list_iter_begin(crtc->dev, &conn_iter);
-	drm_for_each_connector_iter(connector, &conn_iter) {
-		struct drm_connector_state *conn_state = get_state(state, connector);
+	struct drm_encoder *encoder;
 
-		if (!conn_state)
-			continue;
+	WARN_ON(hweight32(state->encoder_mask) > 1);
 
-		if (conn_state->crtc == crtc) {
-			drm_connector_list_iter_end(&conn_iter);
-			return connector->encoder;
-		}
-	}
-	drm_connector_list_iter_end(&conn_iter);
+	drm_for_each_encoder_mask(encoder, crtc->dev, state->encoder_mask)
+		return encoder;
 
 	return NULL;
 }
@@ -550,8 +538,7 @@ static void vc4_crtc_atomic_disable(struct drm_crtc *crtc,
 	struct drm_crtc_state *old_state = drm_atomic_get_old_crtc_state(state,
 									 crtc);
 	struct vc4_crtc_state *old_vc4_state = to_vc4_crtc_state(old_state);
-	struct drm_encoder *encoder = vc4_get_crtc_encoder(crtc, state,
-							   drm_atomic_get_old_connector_state);
+	struct drm_encoder *encoder = vc4_get_crtc_encoder(crtc, old_state);
 	struct drm_device *dev = crtc->dev;
 
 	require_hvs_enabled(dev);
@@ -578,10 +565,11 @@ static void vc4_crtc_atomic_disable(struct drm_crtc *crtc,
 static void vc4_crtc_atomic_enable(struct drm_crtc *crtc,
 				   struct drm_atomic_state *state)
 {
+	struct drm_crtc_state *new_state = drm_atomic_get_new_crtc_state(state,
+									 crtc);
 	struct drm_device *dev = crtc->dev;
 	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
-	struct drm_encoder *encoder = vc4_get_crtc_encoder(crtc, state,
-							   drm_atomic_get_new_connector_state);
+	struct drm_encoder *encoder = vc4_get_crtc_encoder(crtc, new_state);
 	struct vc4_encoder *vc4_encoder = to_vc4_encoder(encoder);
 
 	require_hvs_enabled(dev);

drivers/gpu/drm/vc4/vc4_drv.h

@@ -518,9 +518,7 @@ vc4_crtc_to_vc4_pv_data(const struct vc4_crtc *crtc)
 }
 
 struct drm_encoder *vc4_get_crtc_encoder(struct drm_crtc *crtc,
-					 struct drm_atomic_state *state,
-					 struct drm_connector_state *(*get_state)(struct drm_atomic_state *state,
-										  struct drm_connector *connector));
+					 struct drm_crtc_state *state);
 
 struct vc4_crtc_state {
 	struct drm_crtc_state base;