drm/atomic: Fix remaining places where !funcs->best_encoder is valid

Adapt drm_pick_crtcs() and update_connector_routing() to fallback to
drm_atomic_helper_best_encoder() if funcs->best_encoder() is NULL so
that DRM drivers can leave this hook unassigned if they know they want
to use drm_atomic_helper_best_encoder().

Update the vtables documentation accordingly.
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1465300095-16971-2-git-send-email-boris.brezillon@free-electrons.com

drivers/gpu/drm/drm_atomic_helper.c

@@ -300,8 +300,10 @@ update_connector_routing(struct drm_atomic_state *state,
 	if (funcs->atomic_best_encoder)
 		new_encoder = funcs->atomic_best_encoder(connector,
 							 connector_state);
-	else
+	else if (funcs->best_encoder)
 		new_encoder = funcs->best_encoder(connector);
+	else
+		new_encoder = drm_atomic_helper_best_encoder(connector);
 
 	if (!new_encoder) {
 		DRM_DEBUG_ATOMIC("No suitable encoder found for [CONNECTOR:%d:%s]\n",

drivers/gpu/drm/drm_fb_helper.c

@@ -1971,7 +1971,18 @@ static int drm_pick_crtcs(struct drm_fb_helper *fb_helper,
 		my_score++;
 
 	connector_funcs = connector->helper_private;
+
+	/*
+	 * If the DRM device implements atomic hooks and ->best_encoder() is
+	 * NULL we fallback to the default drm_atomic_helper_best_encoder()
+	 * helper.
+	 */
+	if (fb_helper->dev->mode_config.funcs->atomic_commit &&
+	    !connector_funcs->best_encoder)
+		encoder = drm_atomic_helper_best_encoder(connector);
+	else
 		encoder = connector_funcs->best_encoder(connector);
+
 	if (!encoder)
 		goto out;
 

include/drm/drm_modeset_helper_vtables.h

@@ -736,6 +736,11 @@ struct drm_connector_helper_funcs {
 	 * inspect dynamic configuration state should instead use
 	 * @atomic_best_encoder.
 	 *
+	 * You can leave this function to NULL if the connector is only
+	 * attached to a single encoder and you are using the atomic helpers.
+	 * In this case, the core will call drm_atomic_helper_best_encoder()
+	 * for you.
+	 *
 	 * RETURNS:
 	 *
 	 * Encoder that should be used for the given connector and connector
@@ -752,8 +757,9 @@ struct drm_connector_helper_funcs {
 	 * need to select the best encoder depending upon the desired
 	 * configuration and can't select it statically.
 	 *
-	 * This function is used by drm_atomic_helper_check_modeset() and either
-	 * this or @best_encoder is required.
+	 * This function is used by drm_atomic_helper_check_modeset().
+	 * If it is not implemented, the core will fallback to @best_encoder
+	 * (or drm_atomic_helper_best_encoder() if @best_encoder is NULL).
 	 *
 	 * NOTE:
 	 *