drm: rcar-du: lvds: Fix stop sequence

According to hardware manual, LVDCR0 register must be cleared bit by bit
when disabling LVDS.
Signed-off-by: Koji Matsuoka <koji.matsuoka.xm@renesas.com>
Signed-off-by: LUU HOAI <hoai.luu.ub@renesas.com>
[tomi.valkeinen: simplified the code a bit]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

drivers/gpu/drm/rcar-du/rcar_lvds.c

@@ -83,6 +83,11 @@ struct rcar_lvds {
 #define bridge_to_rcar_lvds(b) \
 	container_of(b, struct rcar_lvds, bridge)
 
+static u32 rcar_lvds_read(struct rcar_lvds *lvds, u32 reg)
+{
+	return ioread32(lvds->mmio + reg);
+}
+
 static void rcar_lvds_write(struct rcar_lvds *lvds, u32 reg, u32 data)
 {
 	iowrite32(data, lvds->mmio + reg);
@@ -544,6 +549,32 @@ static void rcar_lvds_atomic_disable(struct drm_bridge *bridge,
 				     struct drm_bridge_state *old_bridge_state)
 {
 	struct rcar_lvds *lvds = bridge_to_rcar_lvds(bridge);
+	u32 lvdcr0;
+
+	/*
+	 * Clear the LVDCR0 bits in the order specified by the hardware
+	 * documentation, ending with a write of 0 to the full register to
+	 * clear all remaining bits.
+	 */
+	lvdcr0 = rcar_lvds_read(lvds, LVDCR0);
+
+	lvdcr0 &= ~LVDCR0_LVRES;
+	rcar_lvds_write(lvds, LVDCR0, lvdcr0);
+
+	if (lvds->info->quirks & RCAR_LVDS_QUIRK_GEN3_LVEN) {
+		lvdcr0 &= ~LVDCR0_LVEN;
+		rcar_lvds_write(lvds, LVDCR0, lvdcr0);
+	}
+
+	if (lvds->info->quirks & RCAR_LVDS_QUIRK_PWD) {
+		lvdcr0 &= ~LVDCR0_PWD;
+		rcar_lvds_write(lvds, LVDCR0, lvdcr0);
+	}
+
+	if (!(lvds->info->quirks & RCAR_LVDS_QUIRK_EXT_PLL)) {
+		lvdcr0 &= ~LVDCR0_PLLON;
+		rcar_lvds_write(lvds, LVDCR0, lvdcr0);
+	}
 
 	rcar_lvds_write(lvds, LVDCR0, 0);
 	rcar_lvds_write(lvds, LVDCR1, 0);