[v3 2/2] backlight: Add DisplayPort aux backlight driver

[Rajeev Nandan]

Add backlight driver for the panels supporting backlight control
using DPCD registers on the DisplayPort aux channel.

Changes in v2:
- New (most of the code reused from drm_dp_aux_backlight.c of v1)

Changes in v3:
- Add missing ';' to fix module compilation (kernel test bot)

Signed-off-by: Rajeev Nandan <rajeevny@xxxxxxxxxxxxxx>
---
 drivers/video/backlight/Kconfig            |   7 +
 drivers/video/backlight/Makefile           |   1 +
 drivers/video/backlight/dp_aux_backlight.c | 245 +++++++++++++++++++++++++++++
 3 files changed, 253 insertions(+)
 create mode 100644 drivers/video/backlight/dp_aux_backlight.c

diff --git a/drivers/video/backlight/Kconfig b/drivers/video/backlight/Kconfig
index d83c87b..82c88f0 100644
--- a/drivers/video/backlight/Kconfig
+++ b/drivers/video/backlight/Kconfig
@@ -456,6 +456,13 @@ config BACKLIGHT_LED
 	  If you have a LCD backlight adjustable by LED class driver, say Y
 	  to enable this driver.
 
+config BACKLIGHT_DP_AUX
+       tristate "DisplayPort aux backlight driver"
+       depends on DRM && DRM_KMS_HELPER
+       help
+         If you have a panel backlight controlled by DPCD registers
+         on the DisplayPort aux channel, say Y to enable this driver.
+
 endif # BACKLIGHT_CLASS_DEVICE
 
 endmenu
diff --git a/drivers/video/backlight/Makefile b/drivers/video/backlight/Makefile
index 685f3f1..ba23c7c 100644
--- a/drivers/video/backlight/Makefile
+++ b/drivers/video/backlight/Makefile
@@ -57,3 +57,4 @@ obj-$(CONFIG_BACKLIGHT_WM831X)		+= wm831x_bl.o
 obj-$(CONFIG_BACKLIGHT_ARCXCNN) 	+= arcxcnn_bl.o
 obj-$(CONFIG_BACKLIGHT_RAVE_SP)		+= rave-sp-backlight.o
 obj-$(CONFIG_BACKLIGHT_LED)		+= led_bl.o
+obj-$(CONFIG_BACKLIGHT_DP_AUX)		+= dp_aux_backlight.o
diff --git a/drivers/video/backlight/dp_aux_backlight.c b/drivers/video/backlight/dp_aux_backlight.c
new file mode 100644
index 00000000..3398383
--- /dev/null
+++ b/drivers/video/backlight/dp_aux_backlight.c
@@ -0,0 +1,245 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Backlight driver to control the brightness over DisplayPort aux channel.
+ */
+
+#include <linux/backlight.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <drm/drm_dp_helper.h>
+
+#define DP_AUX_MAX_BRIGHTNESS		0xffff
+
+/**
+ * struct dp_aux_backlight - DisplayPort aux backlight data
+ * @dev: pointer to our device.
+ * @aux: the DisplayPort aux channel.
+ * @enable_gpio: the backlight enable gpio.
+ * @enabled: true if backlight is enabled else false.
+ */
+struct dp_aux_backlight {
+	struct device *dev;
+	struct drm_dp_aux *aux;
+	struct gpio_desc *enable_gpio;
+	bool enabled;
+};
+
+static struct drm_dp_aux *i2c_to_aux(struct i2c_adapter *i2c)
+{
+	return container_of(i2c, struct drm_dp_aux, ddc);
+}
+
+static int dp_aux_backlight_enable(struct dp_aux_backlight *aux_bl)
+{
+	u8 val = 0;
+	int ret;
+
+	if (aux_bl->enabled)
+		return 0;
+
+	/* Set backlight control mode */
+	ret = drm_dp_dpcd_readb(aux_bl->aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
+				&val);
+	if (ret < 0)
+		return ret;
+
+	val &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
+	val |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
+	ret = drm_dp_dpcd_writeb(aux_bl->aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
+				 val);
+	if (ret < 0)
+		return ret;
+
+	/* Enable backlight */
+	ret = drm_dp_dpcd_readb(aux_bl->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
+				&val);
+	if (ret < 0)
+		return ret;
+
+	val |= DP_EDP_BACKLIGHT_ENABLE;
+	ret = drm_dp_dpcd_writeb(aux_bl->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
+				 val);
+	if (ret < 0)
+		return ret;
+
+	if (aux_bl->enable_gpio)
+		gpiod_set_value(aux_bl->enable_gpio, 1);
+
+	aux_bl->enabled = true;
+
+	return 0;
+}
+
+static int dp_aux_backlight_disable(struct dp_aux_backlight *aux_bl)
+{
+	u8 val = 0;
+	int ret;
+
+	if (!aux_bl->enabled)
+		return 0;
+
+	if (aux_bl->enable_gpio)
+		gpiod_set_value(aux_bl->enable_gpio, 0);
+
+	ret = drm_dp_dpcd_readb(aux_bl->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
+				&val);
+	if (ret < 0)
+		return ret;
+
+	val &= ~DP_EDP_BACKLIGHT_ENABLE;
+	ret = drm_dp_dpcd_writeb(aux_bl->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
+				 val);
+	if (ret < 0)
+		return ret;
+
+	aux_bl->enabled = false;
+
+	return 0;
+}
+
+static int dp_aux_backlight_update_status(struct backlight_device *bd)
+{
+	struct dp_aux_backlight *aux_bl = bl_get_data(bd);
+	u16 brightness = backlight_get_brightness(bd);
+	u8 val[2] = { 0x0 };
+	int ret = 0;
+
+	if (brightness > 0) {
+		val[0] = brightness >> 8;
+		val[1] = brightness & 0xff;
+		ret = drm_dp_dpcd_write(aux_bl->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
+					val, sizeof(val));
+		if (ret < 0)
+			return ret;
+
+		dp_aux_backlight_enable(aux_bl);
+	} else {
+		dp_aux_backlight_disable(aux_bl);
+	}
+
+	return 0;
+}
+
+static int dp_aux_backlight_get_brightness(struct backlight_device *bd)
+{
+	struct dp_aux_backlight *aux_bl = bl_get_data(bd);
+	u8 val[2] = { 0x0 };
+	int ret = 0;
+
+	if (backlight_is_blank(bd))
+		return 0;
+
+	ret = drm_dp_dpcd_read(aux_bl->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
+			       &val, sizeof(val));
+	if (ret < 0)
+		return ret;
+
+	return (val[0] << 8 | val[1]);
+}
+
+static const struct backlight_ops aux_bl_ops = {
+	.update_status = dp_aux_backlight_update_status,
+	.get_brightness = dp_aux_backlight_get_brightness,
+};
+
+
+static int dp_aux_backlight_probe(struct platform_device *pdev)
+{
+	struct dp_aux_backlight *aux_bl;
+	struct backlight_device *bd;
+	struct backlight_properties bl_props = { 0 };
+	struct device_node *np;
+	struct i2c_adapter *ddc;
+	int ret = 0;
+	u32 val;
+
+	aux_bl = devm_kzalloc(&pdev->dev, sizeof(*aux_bl), GFP_KERNEL);
+	if (!aux_bl)
+		return -ENOMEM;
+
+	aux_bl->dev = &pdev->dev;
+
+	np = of_parse_phandle(pdev->dev.of_node, "ddc-i2c-bus", 0);
+	if (!np) {
+		dev_err(&pdev->dev, "failed to get aux ddc I2C bus\n");
+		return -ENODEV;
+	}
+
+	ddc = of_find_i2c_adapter_by_node(np);
+	of_node_put(np);
+	if (!ddc)
+		return -EPROBE_DEFER;
+
+	aux_bl->aux = i2c_to_aux(ddc);
+	dev_dbg(&pdev->dev, "using dp aux %s\n", aux_bl->aux->name);
+
+	aux_bl->enable_gpio = devm_gpiod_get_optional(&pdev->dev, "enable",
+					     GPIOD_OUT_LOW);
+	if (IS_ERR(aux_bl->enable_gpio)) {
+		ret = PTR_ERR(aux_bl->enable_gpio);
+		goto free_ddc;
+	}
+
+	val = DP_AUX_MAX_BRIGHTNESS;
+	of_property_read_u32(pdev->dev.of_node, "max-brightness", &val);
+	if (val > DP_AUX_MAX_BRIGHTNESS)
+		val = DP_AUX_MAX_BRIGHTNESS;
+
+	bl_props.max_brightness = val;
+	bl_props.brightness = val;
+	bl_props.type = BACKLIGHT_RAW;
+	bd = devm_backlight_device_register(&pdev->dev, dev_name(&pdev->dev),
+					    &pdev->dev, aux_bl,
+					    &aux_bl_ops, &bl_props);
+	if (IS_ERR(bd)) {
+		ret = PTR_ERR(bd);
+		dev_err(&pdev->dev,
+			      "failed to register backlight (%d)\n", ret);
+		goto free_ddc;
+	}
+
+	platform_set_drvdata(pdev, bd);
+
+	return 0;
+
+free_ddc:
+	if (ddc)
+		put_device(&ddc->dev);
+
+	return ret;
+}
+
+static int dp_aux_backlight_remove(struct platform_device *pdev)
+{
+	struct backlight_device *bd = platform_get_drvdata(pdev);
+	struct dp_aux_backlight *aux_bl = bl_get_data(bd);
+	struct i2c_adapter *ddc = &aux_bl->aux->ddc;
+
+	if (ddc)
+		put_device(&ddc->dev);
+
+	return 0;
+}
+
+static const struct of_device_id dp_aux_bl_of_match_table[] = {
+	{ .compatible = "dp-aux-backlight"},
+	{},
+};
+MODULE_DEVICE_TABLE(of, dp_aux_bl_of_match_table);
+
+static struct platform_driver dp_aux_backlight_driver = {
+	.driver = {
+		.name = "dp-aux-backlight",
+		.of_match_table = dp_aux_bl_of_match_table,
+	},
+	.probe = dp_aux_backlight_probe,
+	.remove = dp_aux_backlight_remove,
+
+};
+module_platform_driver(dp_aux_backlight_driver);
+
+MODULE_DESCRIPTION("DisplayPort aux backlight driver");
+MODULE_LICENSE("GPL v2");
-- 
2.7.4