drm/bridge: it6505: Send DPCD SET_POWER to downstream

Send DPCD SET_POWER command to downstream in .atomic_disable to make the
downstream monitor enter the power down mode, so the device suspend won't
be affected.

Fixes: b5c84a9e ("drm/bridge: add it6505 driver")
Signed-off-by: Pin-Yen Lin <treapking@chromium.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220425134424.1150965-1-treapking@chromium.orgReviewed-by: Robert Foss <robert.foss@linaro.org>

drivers/gpu/drm/bridge/ite-it6505.c

@@ -737,8 +737,9 @@ static int it6505_drm_dp_link_probe(struct drm_dp_aux *aux,
 	return 0;
 }
 
-static int it6505_drm_dp_link_power_up(struct drm_dp_aux *aux,
-				       struct it6505_drm_dp_link *link)
+static int it6505_drm_dp_link_set_power(struct drm_dp_aux *aux,
+					struct it6505_drm_dp_link *link,
+					u8 mode)
 {
 	u8 value;
 	int err;
@@ -752,18 +753,20 @@ static int it6505_drm_dp_link_power_up(struct drm_dp_aux *aux,
 		return err;
 
 	value &= ~DP_SET_POWER_MASK;
-	value |= DP_SET_POWER_D0;
+	value |= mode;
 
 	err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
 	if (err < 0)
 		return err;
 
-	/*
-	 * According to the DP 1.1 specification, a "Sink Device must exit the
-	 * power saving state within 1 ms" (Section 2.5.3.1, Table 5-52, "Sink
-	 * Control Field" (register 0x600).
-	 */
-	usleep_range(1000, 2000);
+	if (mode == DP_SET_POWER_D0) {
+		/*
+		 * According to the DP 1.1 specification, a "Sink Device must
+		 * exit the power saving state within 1 ms" (Section 2.5.3.1,
+		 * Table 5-52, "Sink Control Field" (register 0x600).
+		 */
+		usleep_range(1000, 2000);
+	}
 
 	return 0;
 }
@@ -2624,7 +2627,8 @@ static enum drm_connector_status it6505_detect(struct it6505 *it6505)
 	if (it6505_get_sink_hpd_status(it6505)) {
 		it6505_aux_on(it6505);
 		it6505_drm_dp_link_probe(&it6505->aux, &it6505->link);
-		it6505_drm_dp_link_power_up(&it6505->aux, &it6505->link);
+		it6505_drm_dp_link_set_power(&it6505->aux, &it6505->link,
+					     DP_SET_POWER_D0);
 		it6505->auto_train_retry = AUTO_TRAIN_RETRY;
 
 		if (it6505->dpcd[0] == 0) {
@@ -2960,8 +2964,11 @@ static void it6505_bridge_atomic_disable(struct drm_bridge *bridge,
 
 	DRM_DEV_DEBUG_DRIVER(dev, "start");
 
-	if (it6505->powered)
+	if (it6505->powered) {
 		it6505_video_disable(it6505);
+		it6505_drm_dp_link_set_power(&it6505->aux, &it6505->link,
+					     DP_SET_POWER_D3);
+	}
 }
 
 static enum drm_connector_status