[PATCH 2/2] drm/bridge: ti-sn65dsi86: Expose backlight controls

[Bjorn Andersson]

The TI SN65DSI86 can be configured to generate a PWM pulse on GPIO4,
to be used to drive a backlight driver.

Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
---
 drivers/gpu/drm/bridge/Kconfig        |   1 +
 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 143 +++++++++++++++++++++++++-
 2 files changed, 140 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index 43271c21d3fc..eea310bd88e1 100644
--- a/drivers/gpu/drm/bridge/Kconfig
+++ b/drivers/gpu/drm/bridge/Kconfig
@@ -195,6 +195,7 @@ config DRM_TI_SN65DSI86
 	select REGMAP_I2C
 	select DRM_PANEL
 	select DRM_MIPI_DSI
+	select BACKLIGHT_CLASS_DEVICE
 	help
 	  Texas Instruments SN65DSI86 DSI to eDP Bridge driver
 
diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 5b6e19ecbc84..41e24d0dbd18 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -68,6 +68,7 @@
 #define  SN_GPIO_MUX_OUTPUT			1
 #define  SN_GPIO_MUX_SPECIAL			2
 #define  SN_GPIO_MUX_MASK			0x3
+#define  SN_GPIO_MUX_SHIFT(gpio)		((gpio) * 2)
 #define SN_AUX_WDATA_REG(x)			(0x64 + (x))
 #define SN_AUX_ADDR_19_16_REG			0x74
 #define SN_AUX_ADDR_15_8_REG			0x75
@@ -86,6 +87,12 @@
 #define SN_ML_TX_MODE_REG			0x96
 #define  ML_TX_MAIN_LINK_OFF			0
 #define  ML_TX_NORMAL_MODE			BIT(0)
+#define SN_PWM_PRE_DIV_REG			0xA0
+#define SN_BACKLIGHT_SCALE_REG			0xA1
+#define SN_BACKLIGHT_REG			0xA3
+#define SN_PWM_CTL_REG				0xA5
+#define  SN_PWM_ENABLE				BIT(1)
+#define  SN_PWM_INVERT				BIT(0)
 #define SN_AUX_CMD_STATUS_REG			0xF4
 #define  AUX_IRQ_STATUS_AUX_RPLY_TOUT		BIT(3)
 #define  AUX_IRQ_STATUS_AUX_SHORT		BIT(5)
@@ -155,6 +162,8 @@ struct ti_sn_bridge {
 	struct gpio_chip		gchip;
 	DECLARE_BITMAP(gchip_output, SN_NUM_GPIOS);
 #endif
+	u32				brightness;
+	u32				max_brightness;
 };
 
 static const struct regmap_range ti_sn_bridge_volatile_ranges[] = {
@@ -173,6 +182,18 @@ static const struct regmap_config ti_sn_bridge_regmap_config = {
 	.cache_type = REGCACHE_NONE,
 };
 
+static void ti_sn_bridge_read_u16(struct ti_sn_bridge *pdata,
+				  unsigned int reg, u16 *val)
+{
+	unsigned int high;
+	unsigned int low;
+
+	regmap_read(pdata->regmap, reg, &low);
+	regmap_read(pdata->regmap, reg + 1, &high);
+
+	*val = high << 8 | low;
+}
+
 static void ti_sn_bridge_write_u16(struct ti_sn_bridge *pdata,
 				   unsigned int reg, u16 val)
 {
@@ -180,6 +201,50 @@ static void ti_sn_bridge_write_u16(struct ti_sn_bridge *pdata,
 	regmap_write(pdata->regmap, reg + 1, val >> 8);
 }
 
+static int ti_sn_backlight_update(struct ti_sn_bridge *pdata)
+{
+	unsigned int pre_div;
+
+	if (!pdata->max_brightness)
+		return 0;
+
+	/* Enable PWM on GPIO4 */
+	regmap_update_bits(pdata->regmap, SN_GPIO_CTRL_REG,
+			   SN_GPIO_MUX_MASK << SN_GPIO_MUX_SHIFT(4 - 1),
+			   SN_GPIO_MUX_SPECIAL << SN_GPIO_MUX_SHIFT(4 - 1));
+
+	if (pdata->brightness) {
+		/* Set max brightness */
+		ti_sn_bridge_write_u16(pdata, SN_BACKLIGHT_SCALE_REG, pdata->max_brightness);
+
+		/* Set brightness */
+		ti_sn_bridge_write_u16(pdata, SN_BACKLIGHT_REG, pdata->brightness);
+
+		/*
+		 * The PWM frequency is derived from the refclk as:
+		 * PWM_FREQ = REFCLK_FREQ / (PWM_PRE_DIV * BACKLIGHT_SCALE + 1)
+		 *
+		 * A hand wavy estimate based on 12MHz refclk and 500Hz desired
+		 * PWM frequency gives us a pre_div resulting in a PWM
+		 * frequency of between 500 and 1600Hz, depending on the actual
+		 * refclk rate.
+		 *
+		 * One is added to avoid high BACKLIGHT_SCALE values to produce
+		 * a pre_div of 0 - which cancels out the large BACKLIGHT_SCALE
+		 * value.
+		 */
+		pre_div = 12000000 / (500 * pdata->max_brightness) + 1;
+		regmap_write(pdata->regmap, SN_PWM_PRE_DIV_REG, pre_div);
+
+		/* Enable PWM */
+		regmap_update_bits(pdata->regmap, SN_PWM_CTL_REG, SN_PWM_ENABLE, SN_PWM_ENABLE);
+	} else {
+		regmap_update_bits(pdata->regmap, SN_PWM_CTL_REG, SN_PWM_ENABLE, 0);
+	}
+
+	return 0;
+}
+
 static int __maybe_unused ti_sn_bridge_resume(struct device *dev)
 {
 	struct ti_sn_bridge *pdata = dev_get_drvdata(dev);
@@ -193,7 +258,7 @@ static int __maybe_unused ti_sn_bridge_resume(struct device *dev)
 
 	gpiod_set_value(pdata->enable_gpio, 1);
 
-	return ret;
+	return ti_sn_backlight_update(pdata);
 }
 
 static int __maybe_unused ti_sn_bridge_suspend(struct device *dev)
@@ -1010,7 +1075,7 @@ static int ti_sn_bridge_gpio_direction_input(struct gpio_chip *chip,
 					     unsigned int offset)
 {
 	struct ti_sn_bridge *pdata = gpiochip_get_data(chip);
-	int shift = offset * 2;
+	int shift = SN_GPIO_MUX_SHIFT(offset);
 	int ret;
 
 	if (!test_and_clear_bit(offset, pdata->gchip_output))
@@ -1038,7 +1103,7 @@ static int ti_sn_bridge_gpio_direction_output(struct gpio_chip *chip,
 					      unsigned int offset, int val)
 {
 	struct ti_sn_bridge *pdata = gpiochip_get_data(chip);
-	int shift = offset * 2;
+	int shift = SN_GPIO_MUX_SHIFT(offset);
 	int ret;
 
 	if (test_and_set_bit(offset, pdata->gchip_output))
@@ -1073,12 +1138,17 @@ static const char * const ti_sn_bridge_gpio_names[SN_NUM_GPIOS] = {
 
 static int ti_sn_setup_gpio_controller(struct ti_sn_bridge *pdata)
 {
+	int ngpio = SN_NUM_GPIOS;
 	int ret;
 
 	/* Only init if someone is going to use us as a GPIO controller */
 	if (!of_property_read_bool(pdata->dev->of_node, "gpio-controller"))
 		return 0;
 
+	/* If GPIO4 is used for backlight, reduce number of gpios */
+	if (pdata->max_brightness)
+		ngpio--;
+
 	pdata->gchip.label = dev_name(pdata->dev);
 	pdata->gchip.parent = pdata->dev;
 	pdata->gchip.owner = THIS_MODULE;
@@ -1092,7 +1162,7 @@ static int ti_sn_setup_gpio_controller(struct ti_sn_bridge *pdata)
 	pdata->gchip.set = ti_sn_bridge_gpio_set;
 	pdata->gchip.can_sleep = true;
 	pdata->gchip.names = ti_sn_bridge_gpio_names;
-	pdata->gchip.ngpio = SN_NUM_GPIOS;
+	pdata->gchip.ngpio = ngpio;
 	pdata->gchip.base = -1;
 	ret = devm_gpiochip_add_data(pdata->dev, &pdata->gchip, pdata);
 	if (ret)
@@ -1159,6 +1229,65 @@ static void ti_sn_bridge_parse_lanes(struct ti_sn_bridge *pdata,
 	pdata->ln_polrs = ln_polrs;
 }
 
+static int ti_sn_backlight_update_status(struct backlight_device *bl)
+{
+	struct ti_sn_bridge *pdata = bl_get_data(bl);
+	int brightness = bl->props.brightness;
+
+	if (bl->props.power != FB_BLANK_UNBLANK ||
+	    bl->props.fb_blank != FB_BLANK_UNBLANK ||
+	    bl->props.state & BL_CORE_FBBLANK) {
+		pdata->brightness = 0;
+	}
+
+	pdata->brightness = brightness;
+
+	return ti_sn_backlight_update(pdata);
+}
+
+static int ti_sn_backlight_get_brightness(struct backlight_device *bl)
+{
+	struct ti_sn_bridge *pdata = bl_get_data(bl);
+	u16 val;
+
+	ti_sn_bridge_read_u16(pdata, SN_BACKLIGHT_REG, &val);
+
+	return val;
+}
+
+const struct backlight_ops ti_sn_backlight_ops = {
+	.update_status = ti_sn_backlight_update_status,
+	.get_brightness = ti_sn_backlight_get_brightness,
+};
+
+static int ti_sn_backlight_init(struct ti_sn_bridge *pdata)
+{
+	struct backlight_properties props = {};
+	struct backlight_device	*bl;
+	struct device *dev = pdata->dev;
+	struct device_node *np = dev->of_node;
+	int ret;
+
+	ret = of_property_read_u32(np, "ti,backlight-scale", &pdata->max_brightness);
+	if (ret == -EINVAL) {
+		return 0;
+	} else if (ret || pdata->max_brightness >= 0xffff) {
+		DRM_ERROR("invalid max-brightness\n");
+		return -EINVAL;
+	}
+
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = pdata->max_brightness;
+	bl = devm_backlight_device_register(dev, "sn65dsi86", dev, pdata,
+					    &ti_sn_backlight_ops, &props);
+	if (IS_ERR(bl)) {
+		DRM_ERROR("failed to register backlight device\n");
+		return PTR_ERR(bl);
+	}
+
+	return 0;
+}
+
 static int ti_sn_bridge_probe(struct i2c_client *client,
 			      const struct i2c_device_id *id)
 {
@@ -1224,6 +1353,12 @@ static int ti_sn_bridge_probe(struct i2c_client *client,
 
 	pm_runtime_enable(pdata->dev);
 
+	ret = ti_sn_backlight_init(pdata);
+	if (ret) {
+		pm_runtime_disable(pdata->dev);
+		return ret;
+	}
+
 	ret = ti_sn_setup_gpio_controller(pdata);
 	if (ret) {
 		pm_runtime_disable(pdata->dev);
-- 
2.28.0