drm/exynos: dp: support hotplug detection via GPIO

Certain bridge chips use a GPIO to indicate the cable status instead
of the I_DP_HPD pin.  This adds an optional device-tree property,
"samsung,hpd-gpio", to the exynos-dp controller which indicates that
the specified GPIO should be used for hotplug detection.
The GPIO is then set up as an edge-triggered interrupt where the
rising edge indicates hotplug-in and the falling edge indicates hotplug-out.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Rahul Sharma <rahul.sharma@samsung.com>
Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

Documentation/devicetree/bindings/video/exynos_dp.txt

@@ -62,6 +62,10 @@ Optional properties for dp-controller:
 	-hsync-active-high:
 		HSYNC polarity configuration.
 			High if defined, Low if not defined
+	-samsung,hpd-gpio:
+		Hotplug detect GPIO.
+			Indicates which GPIO should be used for hotplug
+			detection
 
 Example:
 

drivers/gpu/drm/exynos/exynos_dp_core.c

@@ -18,6 +18,8 @@
 #include <linux/interrupt.h>
 #include <linux/delay.h>
 #include <linux/of.h>
+#include <linux/of_gpio.h>
+#include <linux/gpio.h>
 #include <linux/component.h>
 #include <linux/phy/phy.h>
 #include <video/of_display_timing.h>
@@ -1217,6 +1219,7 @@ static int exynos_dp_bind(struct device *dev, struct device *master, void *data)
 	struct drm_device *drm_dev = data;
 	struct resource *res;
 	struct exynos_dp_device *dp;
+	unsigned int irq_flags;
 
 	int ret = 0;
 
@@ -1254,7 +1257,30 @@ static int exynos_dp_bind(struct device *dev, struct device *master, void *data)
 	if (IS_ERR(dp->reg_base))
 		return PTR_ERR(dp->reg_base);
 
-	dp->irq = platform_get_irq(pdev, 0);
+	dp->hpd_gpio = of_get_named_gpio(dev->of_node, "samsung,hpd-gpio", 0);
+
+	if (gpio_is_valid(dp->hpd_gpio)) {
+		/*
+		 * Set up the hotplug GPIO from the device tree as an interrupt.
+		 * Simply specifying a different interrupt in the device tree
+		 * doesn't work since we handle hotplug rather differently when
+		 * using a GPIO.  We also need the actual GPIO specifier so
+		 * that we can get the current state of the GPIO.
+		 */
+		ret = devm_gpio_request_one(&pdev->dev, dp->hpd_gpio, GPIOF_IN,
+					    "hpd_gpio");
+		if (ret) {
+			dev_err(&pdev->dev, "failed to get hpd gpio\n");
+			return ret;
+		}
+		dp->irq = gpio_to_irq(dp->hpd_gpio);
+		irq_flags = IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING;
+	} else {
+		dp->hpd_gpio = -ENODEV;
+		dp->irq = platform_get_irq(pdev, 0);
+		irq_flags = 0;
+	}
+
 	if (dp->irq == -ENXIO) {
 		dev_err(&pdev->dev, "failed to get irq\n");
 		return -ENODEV;
@@ -1266,8 +1292,8 @@ static int exynos_dp_bind(struct device *dev, struct device *master, void *data)
 
 	exynos_dp_init_dp(dp);
 
-	ret = devm_request_irq(&pdev->dev, dp->irq, exynos_dp_irq_handler, 0,
-				"exynos-dp", dp);
+	ret = devm_request_irq(&pdev->dev, dp->irq, exynos_dp_irq_handler,
+			irq_flags, "exynos-dp", dp);
 	if (ret) {
 		dev_err(&pdev->dev, "failed to request irq\n");
 		return ret;

drivers/gpu/drm/exynos/exynos_dp_core.h

@@ -159,6 +159,7 @@ struct exynos_dp_device {
 	struct work_struct	hotplug_work;
 	struct phy		*phy;
 	int			dpms_mode;
+	int			hpd_gpio;
 
 	struct exynos_drm_panel_info panel;
 };

drivers/gpu/drm/exynos/exynos_dp_reg.c

@@ -13,6 +13,7 @@
 #include <linux/device.h>
 #include <linux/io.h>
 #include <linux/delay.h>
+#include <linux/gpio.h>
 
 #include "exynos_dp_core.h"
 #include "exynos_dp_reg.h"
@@ -326,6 +327,9 @@ void exynos_dp_clear_hotplug_interrupts(struct exynos_dp_device *dp)
 {
 	u32 reg;
 
+	if (gpio_is_valid(dp->hpd_gpio))
+		return;
+
 	reg = HOTPLUG_CHG | HPD_LOST | PLUG;
 	writel(reg, dp->reg_base + EXYNOS_DP_COMMON_INT_STA_4);
 
@@ -337,6 +341,9 @@ void exynos_dp_init_hpd(struct exynos_dp_device *dp)
 {
 	u32 reg;
 
+	if (gpio_is_valid(dp->hpd_gpio))
+		return;
+
 	exynos_dp_clear_hotplug_interrupts(dp);
 
 	reg = readl(dp->reg_base + EXYNOS_DP_SYS_CTL_3);
@@ -348,19 +355,27 @@ enum dp_irq_type exynos_dp_get_irq_type(struct exynos_dp_device *dp)
 {
 	u32 reg;
 
-	/* Parse hotplug interrupt status register */
-	reg = readl(dp->reg_base + EXYNOS_DP_COMMON_INT_STA_4);
+	if (gpio_is_valid(dp->hpd_gpio)) {
+		reg = gpio_get_value(dp->hpd_gpio);
+		if (reg)
+			return DP_IRQ_TYPE_HP_CABLE_IN;
+		else
+			return DP_IRQ_TYPE_HP_CABLE_OUT;
+	} else {
+		/* Parse hotplug interrupt status register */
+		reg = readl(dp->reg_base + EXYNOS_DP_COMMON_INT_STA_4);
 
-	if (reg & PLUG)
-		return DP_IRQ_TYPE_HP_CABLE_IN;
+		if (reg & PLUG)
+			return DP_IRQ_TYPE_HP_CABLE_IN;
 
-	if (reg & HPD_LOST)
-		return DP_IRQ_TYPE_HP_CABLE_OUT;
+		if (reg & HPD_LOST)
+			return DP_IRQ_TYPE_HP_CABLE_OUT;
 
-	if (reg & HOTPLUG_CHG)
-		return DP_IRQ_TYPE_HP_CHANGE;
+		if (reg & HOTPLUG_CHG)
+			return DP_IRQ_TYPE_HP_CHANGE;
 
-	return DP_IRQ_TYPE_UNKNOWN;
+		return DP_IRQ_TYPE_UNKNOWN;
+	}
 }
 
 void exynos_dp_reset_aux(struct exynos_dp_device *dp)
@@ -402,9 +417,14 @@ int exynos_dp_get_plug_in_status(struct exynos_dp_device *dp)
 {
 	u32 reg;
 
-	reg = readl(dp->reg_base + EXYNOS_DP_SYS_CTL_3);
-	if (reg & HPD_STATUS)
-		return 0;
+	if (gpio_is_valid(dp->hpd_gpio)) {
+		if (gpio_get_value(dp->hpd_gpio))
+			return 0;
+	} else {
+		reg = readl(dp->reg_base + EXYNOS_DP_SYS_CTL_3);
+		if (reg & HPD_STATUS)
+			return 0;
+	}
 
 	return -EINVAL;
 }