drm: Do not set connector->encoder in drivers

An encoder is associated with a connector by the DRM core as a result of
setting up a configuration. Drivers using the atomic or legacy helpers
should never set up this link, even if it is a static one.

While at it, try to catch this kind of error in the future by adding a
WARN_ON() in drm_mode_connector_attach_encoder(). Note that this doesn't
cover all the cases, since drivers could set this up after attaching.
Drivers that use the atomic helpers will get a warning later on, though,
so hopefully the two combined cover enough to help people avoid this in
the future.

Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Liviu Dudau <Liviu.Dudau@arm.com>
Cc: Mark yao <mark.yao@rock-chips.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1447694393-24700-1-git-send-email-thierry.reding@gmail.com

drivers/gpu/drm/bridge/dw_hdmi.c

@@ -1648,8 +1648,6 @@ static int dw_hdmi_register(struct drm_device *drm, struct dw_hdmi *hdmi)
 	drm_connector_init(drm, &hdmi->connector, &dw_hdmi_connector_funcs,
 			   DRM_MODE_CONNECTOR_HDMIA);
 
-	hdmi->connector.encoder = encoder;
-
 	drm_mode_connector_attach_encoder(&hdmi->connector, encoder);
 
 	return 0;

drivers/gpu/drm/drm_crtc.c

@@ -5054,6 +5054,20 @@ 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;

drivers/gpu/drm/i2c/tda998x_drv.c

@@ -1439,7 +1439,6 @@ static int tda998x_bind(struct device *dev, struct device *master, void *data)
 	if (ret)
 		goto err_sysfs;
 
-	priv->connector.encoder = &priv->encoder;
 	drm_mode_connector_attach_encoder(&priv->connector, &priv->encoder);
 
 	return 0;

drivers/gpu/drm/imx/parallel-display.c

@@ -204,8 +204,6 @@ static int imx_pd_register(struct drm_device *drm,
 
 	drm_mode_connector_attach_encoder(&imxpd->connector, &imxpd->encoder);
 
-	imxpd->connector.encoder = &imxpd->encoder;
-
 	return 0;
 }
 

drivers/gpu/drm/shmobile/shmob_drm_crtc.c

@@ -739,8 +739,6 @@ int shmob_drm_connector_create(struct shmob_drm_device *sdev,
 	if (ret < 0)
 		goto err_backlight;
 
-	connector->encoder = encoder;
-
 	drm_helper_connector_dpms(connector, DRM_MODE_DPMS_OFF);
 	drm_object_property_set_value(&connector->base,
 		sdev->ddev->mode_config.dpms_property, DRM_MODE_DPMS_OFF);