drm/vc4: Respect GPIO_ACTIVE_LOW on HDMI HPD if set in the devicetree.

The original Raspberry Pi had the GPIO active high, but the later
models are active low.  The DT GPIO bindings allow specifying the
active flag, except that it doesn't get propagated to the gpiodesc, so
you have to handle it yourself.
Signed-off-by: Eric Anholt <eric@anholt.net>
Tested-by: Daniel Stone <daniels@collabora.com>

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -47,6 +47,7 @@ struct vc4_hdmi {
 	void __iomem *hdmicore_regs;
 	void __iomem *hd_regs;
 	int hpd_gpio;
+	bool hpd_active_low;
 
 	struct clk *pixel_clock;
 	struct clk *hsm_clock;
@@ -166,7 +167,8 @@ vc4_hdmi_connector_detect(struct drm_connector *connector, bool force)
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 
 	if (vc4->hdmi->hpd_gpio) {
-		if (gpio_get_value_cansleep(vc4->hdmi->hpd_gpio))
+		if (gpio_get_value_cansleep(vc4->hdmi->hpd_gpio) ^
+		    vc4->hdmi->hpd_active_low)
 			return connector_status_connected;
 		else
 			return connector_status_disconnected;
@@ -517,11 +519,17 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
 	 * we'll use the HDMI core's register.
 	 */
 	if (of_find_property(dev->of_node, "hpd-gpios", &value)) {
-		hdmi->hpd_gpio = of_get_named_gpio(dev->of_node, "hpd-gpios", 0);
+		enum of_gpio_flags hpd_gpio_flags;
+
+		hdmi->hpd_gpio = of_get_named_gpio_flags(dev->of_node,
+							 "hpd-gpios", 0,
+							 &hpd_gpio_flags);
 		if (hdmi->hpd_gpio < 0) {
 			ret = hdmi->hpd_gpio;
 			goto err_unprepare_hsm;
 		}
+
+		hdmi->hpd_active_low = hpd_gpio_flags & OF_GPIO_ACTIVE_LOW;
 	}
 
 	vc4->hdmi = hdmi;