backlight: ktz8866: Add support for Kinetic KTZ8866 backlight

Add support for Kinetic KTZ8866 backlight, which is used in
Xiaomi tablet, Mi Pad 5 series. This driver lightly based on
downstream implementation [1].
[1] https://github.com/MiCode/Xiaomi_Kernel_OpenSource/blob/elish-r-oss/drivers/video/backlight/ktz8866.c

Signed-off-by: Jianhua Lu <lujianhua000@gmail.com>

MAINTAINERS

@@ -11674,6 +11674,12 @@ M:	John Hawley <warthog9@eaglescrag.net>
 S:	Maintained
 F:	tools/testing/ktest
 
+KTZ8866 BACKLIGHT DRIVER
+M:	Jianhua Lu <lujianhua000@gmail.com>
+S:	Maintained
+F:	Documentation/devicetree/bindings/leds/backlight/kinetic,ktz8866.yaml
+F:	drivers/video/backlight/ktz8866.c
+
 L3MDEV
 M:	David Ahern <dsahern@kernel.org>
 L:	netdev@vger.kernel.org

drivers/video/backlight/Kconfig

@@ -190,6 +190,14 @@ config BACKLIGHT_KTD253
 	  which is a 1-wire GPIO-controlled backlight found in some mobile
 	  phones.
 
+config BACKLIGHT_KTZ8866
+	tristate "Backlight Driver for Kinetic KTZ8866"
+	depends on I2C
+	select REGMAP_I2C
+	help
+		Say Y to enable the backlight driver for the Kinetic KTZ8866
+		found in Xiaomi Mi Pad 5 series.
+
 config BACKLIGHT_LM3533
 	tristate "Backlight Driver for LM3533"
 	depends on MFD_LM3533

drivers/video/backlight/Makefile

@@ -36,6 +36,7 @@ obj-$(CONFIG_BACKLIGHT_HP680)		+= hp680_bl.o
 obj-$(CONFIG_BACKLIGHT_HP700)		+= jornada720_bl.o
 obj-$(CONFIG_BACKLIGHT_IPAQ_MICRO)	+= ipaq_micro_bl.o
 obj-$(CONFIG_BACKLIGHT_KTD253)		+= ktd253-backlight.o
+obj-$(CONFIG_BACKLIGHT_KTZ8866)		+= ktz8866.o
 obj-$(CONFIG_BACKLIGHT_LM3533)		+= lm3533_bl.o
 obj-$(CONFIG_BACKLIGHT_LM3630A)		+= lm3630a_bl.o
 obj-$(CONFIG_BACKLIGHT_LM3639)		+= lm3639_bl.o

drivers/video/backlight/ktz8866.c

@@ -0,0 +1,205 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Backlight driver for the Kinetic KTZ8866
+ *
+ * Copyright (C) 2022, 2023 Jianhua Lu <lujianhua000@gmail.com>
+ */
+
+#include <linux/backlight.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+
+#define DEFAULT_BRIGHTNESS 1500
+#define MAX_BRIGHTNESS 2047
+#define REG_MAX 0x15
+
+/* reg */
+#define DEVICE_ID 0x01
+#define BL_CFG1 0x02
+#define BL_CFG2 0x03
+#define BL_BRT_LSB 0x04
+#define BL_BRT_MSB 0x05
+#define BL_EN 0x08
+#define LCD_BIAS_CFG1 0x09
+#define LCD_BIAS_CFG2 0x0A
+#define LCD_BIAS_CFG3 0x0B
+#define LCD_BOOST_CFG 0x0C
+#define OUTP_CFG 0x0D
+#define OUTN_CFG 0x0E
+#define FLAG 0x0F
+#define BL_OPTION1 0x10
+#define BL_OPTION2 0x11
+#define PWM2DIG_LSBs 0x12
+#define PWM2DIG_MSBs 0x13
+#define BL_DIMMING 0x14
+#define PWM_RAMP_TIME 0x15
+
+/* definition */
+#define BL_EN_BIT BIT(6)
+#define LCD_BIAS_EN 0x9F
+#define PWM_HYST 0x5
+
+struct ktz8866 {
+	struct i2c_client *client;
+	struct regmap *regmap;
+	bool led_on;
+};
+
+static const struct regmap_config ktz8866_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = REG_MAX,
+};
+
+static int ktz8866_write(struct ktz8866 *ktz, unsigned int reg,
+			 unsigned int val)
+{
+	return regmap_write(ktz->regmap, reg, val);
+}
+
+static int ktz8866_update_bits(struct ktz8866 *ktz, unsigned int reg,
+			       unsigned int mask, unsigned int val)
+{
+	return regmap_update_bits(ktz->regmap, reg, mask, val);
+}
+
+static int ktz8866_backlight_update_status(struct backlight_device *backlight_dev)
+{
+	struct ktz8866 *ktz = bl_get_data(backlight_dev);
+	unsigned int brightness = backlight_get_brightness(backlight_dev);
+
+	if (!ktz->led_on && brightness > 0) {
+		ktz8866_update_bits(ktz, BL_EN, BL_EN_BIT, BL_EN_BIT);
+		ktz->led_on = true;
+	} else if (brightness == 0) {
+		ktz8866_update_bits(ktz, BL_EN, BL_EN_BIT, 0);
+		ktz->led_on = false;
+		msleep(10);
+	}
+
+	/* Set brightness */
+	ktz8866_write(ktz, BL_BRT_LSB, brightness & 0x7);
+	ktz8866_write(ktz, BL_BRT_MSB, (brightness >> 3) & 0xFF);
+
+	return 0;
+}
+
+static const struct backlight_ops ktz8866_backlight_ops = {
+	.options = BL_CORE_SUSPENDRESUME,
+	.update_status = ktz8866_backlight_update_status,
+};
+
+static void ktz8866_init(struct ktz8866 *ktz)
+{
+	unsigned int val;
+
+	if(of_property_read_u32(ktz->client->dev.of_node, "current-num-sinks", &val))
+		ktz8866_write(ktz, BL_EN, BIT(val) - 1);
+	else
+		/* Enable all 6 current sinks if the number of current sinks isn't specifed. */
+		ktz8866_write(ktz, BL_EN, BIT(6) - 1);
+
+	if(of_property_read_u32(ktz->client->dev.of_node, "current-ramping-time-ms", &val)) {
+		if(val <= 128) {
+			ktz8866_write(ktz, BL_CFG2, BIT(7) | (ilog2(val) << 3) | PWM_HYST);
+		} else {
+			ktz8866_write(ktz, BL_CFG2, BIT(7) | ((5 + val / 64) << 3) | PWM_HYST);
+		}
+	}
+
+	if(of_property_read_u32(ktz->client->dev.of_node, "led-ramping-time-ms", &val)) {
+		if(val == 0) {
+			ktz8866_write(ktz, BL_DIMMING, 0);
+		} else {
+			unsigned int ramp_off_time = ilog2(val) + 1;
+			unsigned int ramp_on_time = ramp_off_time << 4;
+			ktz8866_write(ktz, BL_DIMMING, ramp_on_time | ramp_off_time);
+		}
+	}
+
+	if(of_property_read_bool(ktz->client->dev.of_node, "enable-lcd-bias"))
+		ktz8866_write(ktz, LCD_BIAS_CFG1, LCD_BIAS_EN);
+}
+
+static int ktz8866_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct backlight_device *backlight_dev;
+	struct backlight_properties props;
+	struct ktz8866 *ktz;
+
+	ktz = devm_kzalloc(&client->dev, sizeof(*ktz), GFP_KERNEL);
+	if (!ktz)
+		return -ENOMEM;
+
+	ktz->client = client;
+	ktz->regmap = devm_regmap_init_i2c(client, &ktz8866_regmap_config);
+
+	if (IS_ERR(ktz->regmap)) {
+		dev_err(&client->dev, "failed to init regmap\n");
+		return PTR_ERR(ktz->regmap);
+	}
+
+	memset(&props, 0, sizeof(props));
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = MAX_BRIGHTNESS;
+	props.brightness = DEFAULT_BRIGHTNESS;
+	props.scale = BACKLIGHT_SCALE_LINEAR;
+
+	backlight_dev = devm_backlight_device_register(
+		&client->dev, "ktz8866-backlight", &client->dev, ktz,
+		&ktz8866_backlight_ops, &props);
+
+	if (IS_ERR(backlight_dev)) {
+		dev_err(&client->dev, "failed to register backlight device\n");
+		return PTR_ERR(backlight_dev);
+	}
+
+	ktz8866_init(ktz);
+
+	i2c_set_clientdata(client, backlight_dev);
+	backlight_update_status(backlight_dev);
+
+	return 0;
+}
+
+static void ktz8866_remove(struct i2c_client *client)
+{
+	struct backlight_device *backlight_dev = i2c_get_clientdata(client);
+
+	backlight_dev->props.brightness = 0;
+	backlight_update_status(backlight_dev);
+}
+
+static const struct i2c_device_id ktz8866_ids[] = {
+	{ "ktz8866", 0 },
+	{},
+};
+MODULE_DEVICE_TABLE(i2c, ktz8866_ids);
+
+static const struct of_device_id ktz8866_match_table[] = {
+	{
+		.compatible = "kinetic,ktz8866",
+	},
+	{},
+};
+
+static struct i2c_driver ktz8866_driver = {
+	.driver = {
+		.name = "ktz8866",
+		.of_match_table = ktz8866_match_table,
+	},
+	.probe = ktz8866_probe,
+	.remove = ktz8866_remove,
+	.id_table = ktz8866_ids,
+};
+
+module_i2c_driver(ktz8866_driver);
+
+MODULE_DESCRIPTION("Kinetic KTZ8866 Backlight Driver");
+MODULE_AUTHOR("Jianhua Lu <lujianhua000@gmail.com>");
+MODULE_LICENSE("GPL");