drm/apple: Power DCP off when HDMI port is not connected

Power DCP off after init when the HDMI port is not connected. According
to user reports connecting and disconnecting the HMI port saves ~0.5W on
14-/16-inch Macbook Pros. This was not reproducibable here though but
powering DCP down is correct in any case.

Signed-off-by: Janne Grunau <j@jannau.net>

Author: jannau

drivers/gpu/drm/apple/dcp.c

@@ -581,6 +581,21 @@ int dcp_start(struct platform_device *pdev)
 	return ret;
 }
 
+static void _dcp_poweroff(struct apple_dcp *dcp)
+{
+	switch (dcp->fw_compat) {
+	case DCP_FIRMWARE_V_12_3:
+		iomfb_poweroff_v12_3(dcp);
+		break;
+	case DCP_FIRMWARE_V_13_5:
+		iomfb_poweroff_v13_3(dcp);
+		break;
+	default:
+		WARN_ONCE(true, "Unexpected firmware version: %u\n", dcp->fw_compat);
+		break;
+	}
+}
+
 static int dcp_enable_dp2hdmi_hpd(struct apple_dcp *dcp)
 {
 	// check HPD state before enabling the edge triggered IRQ
@@ -590,6 +605,8 @@ static int dcp_enable_dp2hdmi_hpd(struct apple_dcp *dcp)
 
 		if (connected)
 			dcp_dptx_connect(dcp, 0);
+		else
+			_dcp_poweroff(dcp);
 	}
 
 	if (dcp->hdmi_hpd_irq)
@@ -673,17 +690,7 @@ void dcp_poweroff(struct platform_device *pdev)
 	if (dcp->avep)
 		av_service_disconnect(dcp);
 
-	switch (dcp->fw_compat) {
-	case DCP_FIRMWARE_V_12_3:
-		iomfb_poweroff_v12_3(dcp);
-		break;
-	case DCP_FIRMWARE_V_13_5:
-		iomfb_poweroff_v13_3(dcp);
-		break;
-	default:
-		WARN_ONCE(true, "Unexpected firmware version: %u\n", dcp->fw_compat);
-		break;
-	}
+	_dcp_poweroff(dcp);
 
 	if (dcp->hdmi_hpd) {
 		bool connected = gpiod_get_value_cansleep(dcp->hdmi_hpd);