--- /dev/null
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/backlight.h>
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+
+#define EW_DELAY 150
+#define EW_DET 270
+#define LOW_BIT_HIGH 5
+#define LOW_BIT_LOW (4 * HIGH_BIT_LOW)
+#define HIGH_BIT_LOW 5
+#define HIGH_BIT_HIGH (4 * HIGH_BIT_LOW)
+#define DS 5
+#define EOD_L 10
+#define EOD_H 350
+#define PWR_DOWN_DELAY 2600
+
+#define KTD2801_DEFAULT_BRIGHTNESS 100
+#define KTD2801_MAX_BRIGHTNESS 255
+
+struct ktd2801_backlight {
+ struct device *dev;
+ struct backlight_device *bd;
+ struct gpio_desc *desc;
+ bool was_on;
+};
+
+static int ktd2801_update_status(struct backlight_device *bd)
+{
+ struct ktd2801_backlight *ktd2801 = bl_get_data(bd);
+ u8 brightness = (u8) backlight_get_brightness(bd);
+
+ if (backlight_is_blank(bd)) {
+ gpiod_set_value(ktd2801->desc, 1);
+ udelay(PWR_DOWN_DELAY);
+ ktd2801->was_on = false;
+ return 0;
+ }
+
+ if (!ktd2801->was_on) {
+ gpiod_set_value(ktd2801->desc, 0);
+ udelay(EW_DELAY);
+ gpiod_set_value(ktd2801->desc, 1);
+ udelay(EW_DET);
+ gpiod_set_value(ktd2801->desc, 0);
+ ktd2801->was_on = true;
+ }
+
+ gpiod_set_value(ktd2801->desc, 0);
+ udelay(DS);
+
+ for (int i = 0; i < 8; i++) {
+ u8 next_bit = (brightness & 0x80) >> 7;
+
+ if (!next_bit) {
+ gpiod_set_value(ktd2801->desc, 1);
+ udelay(LOW_BIT_LOW);
+ gpiod_set_value(ktd2801->desc, 0);
+ udelay(LOW_BIT_HIGH);
+ } else {
+ gpiod_set_value(ktd2801->desc, 1);
+ udelay(HIGH_BIT_LOW);
+ gpiod_set_value(ktd2801->desc, 0);
+ udelay(HIGH_BIT_HIGH);
+ }
+ brightness <<= 1;
+ }
+ gpiod_set_value(ktd2801->desc, 1);
+ udelay(EOD_L);
+ gpiod_set_value(ktd2801->desc, 0);
+ udelay(EOD_H);
+ return 0;
+}
+
+static const struct backlight_ops ktd2801_backlight_ops = {
+ .update_status = ktd2801_update_status,
+};
+
+static int ktd2801_backlight_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct backlight_device *bd;
+ struct ktd2801_backlight *ktd2801;
+ u32 brightness, max_brightness;
+ int ret;
+
+ ktd2801 = devm_kzalloc(dev, sizeof(*ktd2801), GFP_KERNEL);
+ if (!ktd2801)
+ return -ENOMEM;
+ ktd2801->dev = dev;
+ ktd2801->was_on = true;
+
+ ret = device_property_read_u32(dev, "max-brightness", &max_brightness);
+ if (ret)
+ max_brightness = KTD2801_MAX_BRIGHTNESS;
+ if (max_brightness > KTD2801_MAX_BRIGHTNESS) {
+ dev_err(dev, "illegal max brightness specified\n");
+ max_brightness = KTD2801_MAX_BRIGHTNESS;
+ }
+
+ ret = device_property_read_u32(dev, "default-brightness", &brightness);
+ if (ret)
+ brightness = KTD2801_DEFAULT_BRIGHTNESS;
+ if (brightness > max_brightness) {
+ dev_err(dev, "default brightness exceeds max\n");
+ brightness = max_brightness;
+ }
+
+ ktd2801->desc = devm_gpiod_get(dev, "enable", GPIOD_OUT_LOW);
+ if (IS_ERR(ktd2801->desc))
+ return dev_err_probe(dev, PTR_ERR(ktd2801->desc),
+ "failed to get backlight GPIO");
+ gpiod_set_consumer_name(ktd2801->desc, dev_name(dev));
+
+ bd = devm_backlight_device_register(dev, dev_name(dev), dev, ktd2801,
+ &ktd2801_backlight_ops, NULL);
+ if (IS_ERR(bd))
+ return dev_err_probe(dev, PTR_ERR(bd),
+ "failed to register backlight");
+
+ bd->props.max_brightness = max_brightness;
+ bd->props.brightness = brightness;
+
+ ktd2801->bd = bd;
+ platform_set_drvdata(pdev, bd);
+ backlight_update_status(bd);
+
+ return 0;
+}
+
+static const struct of_device_id ktd2801_of_match[] = {
+ { .compatible = "kinetic,ktd2801" },
+ { }
+};
+MODULE_DEVICE_TABLE(of, ktd2801_of_match);
+
+static struct platform_driver ktd2801_backlight_driver = {
+ .driver = {
+ .name = "ktd2801-backlight",
+ .of_match_table = ktd2801_of_match,
+ },
+ .probe = ktd2801_backlight_probe,
+};
+module_platform_driver(ktd2801_backlight_driver);
+
+MODULE_AUTHOR("Duje Mihanović <duje.mihanovic@skole.hr>");
+MODULE_DESCRIPTION("Kinetic KTD2801 Backlight Driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:ktd2801-backlight");