panel-dt/panel-lvds: switch sel6-8-gpio to low in unprepare

There is an issue with a display showing artifacts after leaving the display
blank for some time. If sel6_8 line stays high during the power-off of the
display, the display gets side-powered by the sel6_8 line. And the power
sequence during the next power up does not reset the display in a good state.

So switch the sel6_8 gpio to low, when the VDD-LCD is powered of, and enable it
to the correct state, just before the VDD-LCD is powered on again.

(cherry picked from commit 4f570f563b1ea85d901b8db98af6ad629c4aa1ba)

sel68

drivers/gpu/drm/panel/panel-dt.c

@@ -145,6 +145,12 @@ static int panel_dt_unprepare(struct drm_panel *panel)
 
 	gpiod_set_value_cansleep(p->enable_gpio, 0);
 
+	/* Set sel6_8_gpio to low when powering off the display to prevent it
+	 * from being side-powered by the sel6_8 line.
+	 */
+	if (p->sel6_8_gpio)
+		gpiod_set_value_cansleep(p->sel6_8_gpio, 0);
+
 	regulator_disable(p->supply);
 
 	if (p->delay.unprepare)

drivers/gpu/drm/panel/panel-lvds.c

@@ -54,6 +54,13 @@ static int panel_lvds_unprepare(struct drm_panel *panel)
 	if (lvds->enable_gpio)
 		gpiod_set_value_cansleep(lvds->enable_gpio, 0);
 
+
+	/* Set sel6_8_gpio to low when powering off the display to prevent it
+	 * from being side-powered by the sel6_8 line.
+	 */
+	if (lvds->sel6_8_gpio)
+		gpiod_set_value_cansleep(lvds->sel6_8_gpio, 0);
+
 	if (lvds->supply)
 		regulator_disable(lvds->supply);