drm: add helper functions to retrieve old and new crtc

Add new helper functions, drm_atomic_get_old_crtc_for_encoder
and drm_atomic_get_new_crtc_for_encoder to retrieve the
corresponding crtc for the encoder.

Signed-off-by: Sankeerth Billakanti <[e-mail]>
Signed-off-by: Vinod Polimera <[e-mail]>
Reviewed-by: Douglas Anderson <[e-mail]>
Reviewed-by: Daniel Vetter <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/524718/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

drivers/gpu/drm/drm_atomic.c

···
 EXPORT_SYMBOL(drm_atomic_get_new_connector_for_encoder);
 
 /**
+ * drm_atomic_get_old_crtc_for_encoder - Get old crtc for an encoder
+ * @state: Atomic state
+ * @encoder: The encoder to fetch the crtc state for
+ *
+ * This function finds and returns the crtc that was connected to @encoder
+ * as specified by the @state.
+ *
+ * Returns: The old crtc connected to @encoder, or NULL if the encoder is
+ * not connected.
+ */
+struct drm_crtc *
+drm_atomic_get_old_crtc_for_encoder(struct drm_atomic_state *state,
+				    struct drm_encoder *encoder)
+{
+	struct drm_connector *connector;
+	struct drm_connector_state *conn_state;
+
+	connector = drm_atomic_get_old_connector_for_encoder(state, encoder);
+	if (!connector)
+		return NULL;
+
+	conn_state = drm_atomic_get_old_connector_state(state, connector);
+	if (!conn_state)
+		return NULL;
+
+	return conn_state->crtc;
+}
+EXPORT_SYMBOL(drm_atomic_get_old_crtc_for_encoder);
+
+/**
+ * drm_atomic_get_new_crtc_for_encoder - Get new crtc for an encoder
+ * @state: Atomic state
+ * @encoder: The encoder to fetch the crtc state for
+ *
+ * This function finds and returns the crtc that will be connected to @encoder
+ * as specified by the @state.
+ *
+ * Returns: The new crtc connected to @encoder, or NULL if the encoder is
+ * not connected.
+ */
+struct drm_crtc *
+drm_atomic_get_new_crtc_for_encoder(struct drm_atomic_state *state,
+				    struct drm_encoder *encoder)
+{
+	struct drm_connector *connector;
+	struct drm_connector_state *conn_state;
+
+	connector = drm_atomic_get_new_connector_for_encoder(state, encoder);
+	if (!connector)
+		return NULL;
+
+	conn_state = drm_atomic_get_new_connector_state(state, connector);
+	if (!conn_state)
+		return NULL;
+
+	return conn_state->crtc;
+}
+EXPORT_SYMBOL(drm_atomic_get_new_crtc_for_encoder);
+
+/**
  * drm_atomic_get_connector_state - get connector state
  * @state: global atomic state object
  * @connector: connector to get state object for

include/drm/drm_atomic.h

···
 drm_atomic_get_new_connector_for_encoder(const struct drm_atomic_state *state,
 					 struct drm_encoder *encoder);
 
+struct drm_crtc *
+drm_atomic_get_old_crtc_for_encoder(struct drm_atomic_state *state,
+					 struct drm_encoder *encoder);
+struct drm_crtc *
+drm_atomic_get_new_crtc_for_encoder(struct drm_atomic_state *state,
+					 struct drm_encoder *encoder);
+
 /**
  * drm_atomic_get_existing_crtc_state - get CRTC state, if it exists
  * @state: global atomic state object