drm/nouveau: do not forcibly power on lvds panels

This fix was put in place to fix a bug where the eDP panel on certain
laptops fails to respond over the aux channel after suspend.

It appears that on some systems (Dell M6600, with LVDS panel) there's a
very bad interaction with the eDP init table that causes the SOR to get
very confused and not drive the panel correctly, leading to bleed.

A DPMS off/on cycle is enough to bring it back, but, this will avoid the
problem by not touching the panel GPIOs at times we're not meant to.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_connector.c

@@ -127,12 +127,26 @@ nouveau_connector_ddc_detect(struct drm_connector *connector,
 			     struct nouveau_encoder **pnv_encoder)
 {
 	struct drm_device *dev = connector->dev;
+	struct nouveau_connector *nv_connector = nouveau_connector(connector);
 	struct nouveau_drm *drm = nouveau_drm(dev);
+	struct nouveau_gpio *gpio = nouveau_gpio(drm->device);
 	struct nouveau_i2c *i2c = nouveau_i2c(drm->device);
-	int i;
+	struct nouveau_i2c_port *port = NULL;
+	int i, panel = -ENODEV;
+
+	/* eDP panels need powering on by us (if the VBIOS doesn't default it
+	 * to on) before doing any AUX channel transactions.  LVDS panel power
+	 * is handled by the SOR itself, and not required for LVDS DDC.
+	 */
+	if (nv_connector->type == DCB_CONNECTOR_eDP) {
+		panel = gpio->get(gpio, 0, DCB_GPIO_PANEL_POWER, 0xff);
+		if (panel == 0) {
+			gpio->set(gpio, 0, DCB_GPIO_PANEL_POWER, 0xff, 1);
+			msleep(300);
+		}
+	}
 
 	for (i = 0; i < DRM_CONNECTOR_MAX_ENCODER; i++) {
-		struct nouveau_i2c_port *port = NULL;
 		struct nouveau_encoder *nv_encoder;
 		struct drm_mode_object *obj;
 		int id;
@@ -150,11 +164,19 @@ nouveau_connector_ddc_detect(struct drm_connector *connector,
 			port = i2c->find(i2c, nv_encoder->dcb->i2c_index);
 		if (port && nv_probe_i2c(port, 0x50)) {
 			*pnv_encoder = nv_encoder;
-			return port;
+			break;
 		}
+
+		port = NULL;
 	}
 
-	return NULL;
+	/* eDP panel not detected, restore panel power GPIO to previous
+	 * state to avoid confusing the SOR for other output types.
+	 */
+	if (!port && panel == 0)
+		gpio->set(gpio, 0, DCB_GPIO_PANEL_POWER, 0xff, panel);
+
+	return port;
 }
 
 static struct nouveau_encoder *

drivers/gpu/drm/nouveau/nouveau_display.c

@@ -225,15 +225,6 @@ nouveau_display_init(struct drm_device *dev)
 	if (ret)
 		return ret;
 
-	/* power on internal panel if it's not already.  the init tables of
-	 * some vbios default this to off for some reason, causing the
-	 * panel to not work after resume
-	 */
-	if (gpio && gpio->get(gpio, 0, DCB_GPIO_PANEL_POWER, 0xff) == 0) {
-		gpio->set(gpio, 0, DCB_GPIO_PANEL_POWER, 0xff, 1);
-		msleep(300);
-	}
-
 	/* enable polling for external displays */
 	drm_kms_helper_poll_enable(dev);