UPSTREAM: drm: Do not set connector->encoder in drivers

[firefly-linux-kernel-4.4.55.git] / drivers / gpu / drm / drm_crtc.c

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 7febc7dc6e68ddd724706a5632296d8b42560848..35af30cedb83237a14187d737716954a264790bb 100644 (file)
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -5153,6 +5153,20 @@ int drm_mode_connector_attach_encoder(struct drm_connector *connector,
 {
        int i;
 
+       /*
+        * In the past, drivers have attempted to model the static association
+        * of connector to encoder in simple connector/encoder devices using a
+        * direct assignment of connector->encoder = encoder. This connection
+        * is a logical one and the responsibility of the core, so drivers are
+        * expected not to mess with this.
+        *
+        * Note that the error return should've been enough here, but a large
+        * majority of drivers ignores the return value, so add in a big WARN
+        * to get people's attention.
+        */
+       if (WARN_ON(connector->encoder))
+               return -EINVAL;
+
        for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
                if (connector->encoder_ids[i] == 0) {
                        connector->encoder_ids[i] = encoder->base.id;