On 05/10/2023 20:49, Duje Mihanović wrote:

Add driver for the Kinetic KTD2801 backlight driver.

Signed-off-by: Duje Mihanović <duje.mihanovic@skole.hr>
---
 MAINTAINERS                                 |   6 ++
 drivers/video/backlight/Kconfig             |   7 ++
 drivers/video/backlight/Makefile            |   1 +
 drivers/video/backlight/ktd2801-backlight.c | 151 ++++++++++++++++++++++++++++
 4 files changed, 165 insertions(+)

...

+
+#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;

s/desc/enable_gpio/ or something similar. desc is totally not related.

+	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);

Hm, why device is kept off after this? Setting 0 means enable GPIO is
logical 0.

+	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);

OUT_LOW is keep it disabled, so is this intentional?

+	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 [off-list ref]");
+MODULE_DESCRIPTION("Kinetic KTD2801 Backlight Driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:ktd2801-backlight");

You should not need MODULE_ALIAS() in normal cases. If you need it,
usually it means your device ID table is wrong.

Best regards,
Krzysztof