drm: sun4i: Add support for enabling DDC I2C bus to sun8i_dw_hdmi glue

Orange Pi 3 board requires enabling a voltage shifting circuit via GPIO
for the DDC bus to be usable.

Add support for hdmi-connector node's optional ddc-en-gpios property to
support this use case.
Signed-off-by: Ondrej Jirman <megous@megous.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190806155744.10263-4-megous@megous.com

drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c

@@ -97,10 +97,34 @@ static u32 sun8i_dw_hdmi_find_possible_crtcs(struct drm_device *drm,
 	return crtcs;
 }
 
+static int sun8i_dw_hdmi_find_connector_pdev(struct device *dev,
+					     struct platform_device **pdev_out)
+{
+	struct platform_device *pdev;
+	struct device_node *remote;
+
+	remote = of_graph_get_remote_node(dev->of_node, 1, -1);
+	if (!remote)
+		return -ENODEV;
+
+	if (!of_device_is_compatible(remote, "hdmi-connector")) {
+		of_node_put(remote);
+		return -ENODEV;
+	}
+
+	pdev = of_find_device_by_node(remote);
+	of_node_put(remote);
+	if (!pdev)
+		return -ENODEV;
+
+	*pdev_out = pdev;
+	return 0;
+}
+
 static int sun8i_dw_hdmi_bind(struct device *dev, struct device *master,
 			      void *data)
 {
-	struct platform_device *pdev = to_platform_device(dev);
+	struct platform_device *pdev = to_platform_device(dev), *connector_pdev;
 	struct dw_hdmi_plat_data *plat_data;
 	struct drm_device *drm = data;
 	struct device_node *phy_node;
@@ -150,16 +174,30 @@ static int sun8i_dw_hdmi_bind(struct device *dev, struct device *master,
 		return PTR_ERR(hdmi->regulator);
 	}
 
+	ret = sun8i_dw_hdmi_find_connector_pdev(dev, &connector_pdev);
+	if (!ret) {
+		hdmi->ddc_en = gpiod_get_optional(&connector_pdev->dev,
+						  "ddc-en", GPIOD_OUT_HIGH);
+		platform_device_put(connector_pdev);
+
+		if (IS_ERR(hdmi->ddc_en)) {
+			dev_err(dev, "Couldn't get ddc-en gpio\n");
+			return PTR_ERR(hdmi->ddc_en);
+		}
+	}
+
 	ret = regulator_enable(hdmi->regulator);
 	if (ret) {
 		dev_err(dev, "Failed to enable regulator\n");
-		return ret;
+		goto err_unref_ddc_en;
 	}
 
+	gpiod_set_value(hdmi->ddc_en, 1);
+
 	ret = reset_control_deassert(hdmi->rst_ctrl);
 	if (ret) {
 		dev_err(dev, "Could not deassert ctrl reset control\n");
-		goto err_disable_regulator;
+		goto err_disable_ddc_en;
 	}
 
 	ret = clk_prepare_enable(hdmi->clk_tmds);
@@ -212,8 +250,12 @@ static int sun8i_dw_hdmi_bind(struct device *dev, struct device *master,
 	clk_disable_unprepare(hdmi->clk_tmds);
 err_assert_ctrl_reset:
 	reset_control_assert(hdmi->rst_ctrl);
-err_disable_regulator:
+err_disable_ddc_en:
+	gpiod_set_value(hdmi->ddc_en, 0);
 	regulator_disable(hdmi->regulator);
+err_unref_ddc_en:
+	if (hdmi->ddc_en)
+		gpiod_put(hdmi->ddc_en);
 
 	return ret;
 }
@@ -227,7 +269,11 @@ static void sun8i_dw_hdmi_unbind(struct device *dev, struct device *master,
 	sun8i_hdmi_phy_remove(hdmi);
 	clk_disable_unprepare(hdmi->clk_tmds);
 	reset_control_assert(hdmi->rst_ctrl);
+	gpiod_set_value(hdmi->ddc_en, 0);
 	regulator_disable(hdmi->regulator);
+
+	if (hdmi->ddc_en)
+		gpiod_put(hdmi->ddc_en);
 }
 
 static const struct component_ops sun8i_dw_hdmi_ops = {

drivers/gpu/drm/sun4i/sun8i_dw_hdmi.h

@@ -9,6 +9,7 @@
 #include <drm/bridge/dw_hdmi.h>
 #include <drm/drm_encoder.h>
 #include <linux/clk.h>
+#include <linux/gpio/consumer.h>
 #include <linux/regmap.h>
 #include <linux/regulator/consumer.h>
 #include <linux/reset.h>
@@ -190,6 +191,7 @@ struct sun8i_dw_hdmi {
 	struct regulator		*regulator;
 	const struct sun8i_dw_hdmi_quirks *quirks;
 	struct reset_control		*rst_ctrl;
+	struct gpio_desc		*ddc_en;
 };
 
 static inline struct sun8i_dw_hdmi *