iio: light: driver for Lite-On ltr390

Implements driver for the Ambient/UV Light sensor LTR390.
The driver exposes two ways of getting sensor readings:
  1. Raw UV Counts directly from the sensor
  2. The computed UV Index value with a percision of 2 decimal places

[NOTE] Ambient light sensing has not been implemented yet.

Driver tested on RPi Zero 2W

Datasheet: https://optoelectronics.liteon.com/upload/download/DS86-2015-0004/LTR-390UV_Final_%20DS_V1%201.pdfSigned-off-by: Anshul Dalal <anshulusr@gmail.com>
Link: https://lore.kernel.org/r/20231208102211.413019-2-anshulusr@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

MAINTAINERS

@@ -12663,6 +12663,13 @@ S:	Maintained
 W:	http://linux-test-project.github.io/
 T:	git https://github.com/linux-test-project/ltp.git
 
+LTR390 AMBIENT/UV LIGHT SENSOR DRIVER
+M:	Anshul Dalal <anshulusr@gmail.com>
+L:	linux-iio@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/iio/light/liteon,ltr390.yaml
+F:	drivers/iio/light/ltr390.c
+
 LYNX 28G SERDES PHY DRIVER
 M:	Ioana Ciornei <ioana.ciornei@nxp.com>
 L:	netdev@vger.kernel.org

drivers/iio/light/Kconfig

@@ -362,6 +362,17 @@ config SENSORS_LM3533
 	  changes. The ALS-control output values can be set per zone for the
 	  three current output channels.
 
+config LTR390
+	tristate "LTR-390UV-01 ambient light and UV sensor"
+	depends on I2C
+	select REGMAP_I2C
+	help
+	  If you say yes here you get support for the Lite-On LTR-390UV-01
+	  ambient light and UV sensor.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called ltr390.
+
 config LTR501
 	tristate "LTR-501ALS-01 light sensor"
 	depends on I2C

drivers/iio/light/Makefile

@@ -31,6 +31,7 @@ obj-$(CONFIG_ISL29125)		+= isl29125.o
 obj-$(CONFIG_ISL76682)		+= isl76682.o
 obj-$(CONFIG_JSA1212)		+= jsa1212.o
 obj-$(CONFIG_SENSORS_LM3533)	+= lm3533-als.o
+obj-$(CONFIG_LTR390)		+= ltr390.o
 obj-$(CONFIG_LTR501)		+= ltr501.o
 obj-$(CONFIG_LTRF216A)		+= ltrf216a.o
 obj-$(CONFIG_LV0104CS)		+= lv0104cs.o

drivers/iio/light/ltr390.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * IIO driver for Lite-On LTR390 ALS and UV sensor
+ * (7-bit I2C slave address 0x53)
+ *
+ * Based on the work of:
+ *   Shreeya Patel and Shi Zhigang (LTRF216 Driver)
+ *
+ * Copyright (C) 2023 Anshul Dalal <anshulusr@gmail.com>
+ *
+ * Datasheet:
+ *   https://optoelectronics.liteon.com/upload/download/DS86-2015-0004/LTR-390UV_Final_%20DS_V1%201.pdf
+ *
+ * TODO:
+ *   - Support for configurable gain and resolution
+ *   - Sensor suspend/resume support
+ *   - Add support for reading the ALS
+ *   - Interrupt support
+ */
+
+#include <linux/i2c.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/regmap.h>
+
+#include <linux/iio/iio.h>
+
+#include <asm/unaligned.h>
+
+#define LTR390_MAIN_CTRL      0x00
+#define LTR390_PART_ID	      0x06
+#define LTR390_UVS_DATA	      0x10
+
+#define LTR390_SW_RESET	      BIT(4)
+#define LTR390_UVS_MODE	      BIT(3)
+#define LTR390_SENSOR_ENABLE  BIT(1)
+
+#define LTR390_PART_NUMBER_ID 0xb
+
+/*
+ * At 20-bit resolution (integration time: 400ms) and 18x gain, 2300 counts of
+ * the sensor are equal to 1 UV Index [Datasheet Page#8].
+ *
+ * For the default resolution of 18-bit (integration time: 100ms) and default
+ * gain of 3x, the counts/uvi are calculated as follows:
+ * 2300 / ((3/18) * (100/400)) = 95.83
+ */
+#define LTR390_COUNTS_PER_UVI 96
+
+/*
+ * Window Factor is needed when the device is under Window glass with coated
+ * tinted ink. This is to compensate for the light loss due to the lower
+ * transmission rate of the window glass and helps * in calculating lux.
+ */
+#define LTR390_WINDOW_FACTOR 1
+
+struct ltr390_data {
+	struct regmap *regmap;
+	struct i2c_client *client;
+	/* Protects device from simulataneous reads */
+	struct mutex lock;
+};
+
+static const struct regmap_config ltr390_regmap_config = {
+	.name = "ltr390",
+	.reg_bits = 8,
+	.reg_stride = 1,
+	.val_bits = 8,
+};
+
+static int ltr390_register_read(struct ltr390_data *data, u8 register_address)
+{
+	struct device *dev = &data->client->dev;
+	int ret;
+	u8 recieve_buffer[3];
+
+	guard(mutex)(&data->lock);
+
+	ret = regmap_bulk_read(data->regmap, register_address, recieve_buffer,
+			       sizeof(recieve_buffer));
+	if (ret) {
+		dev_err(dev, "failed to read measurement data");
+		return ret;
+	}
+
+	return get_unaligned_le24(recieve_buffer);
+}
+
+static int ltr390_read_raw(struct iio_dev *iio_device,
+			   struct iio_chan_spec const *chan, int *val,
+			   int *val2, long mask)
+{
+	int ret;
+	struct ltr390_data *data = iio_priv(iio_device);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = ltr390_register_read(data, LTR390_UVS_DATA);
+		if (ret < 0)
+			return ret;
+		*val = ret;
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		*val = LTR390_WINDOW_FACTOR;
+		*val2 = LTR390_COUNTS_PER_UVI;
+		return IIO_VAL_FRACTIONAL;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info ltr390_info = {
+	.read_raw = ltr390_read_raw,
+};
+
+static const struct iio_chan_spec ltr390_channel = {
+	.type = IIO_UVINDEX,
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE)
+};
+
+static int ltr390_probe(struct i2c_client *client)
+{
+	struct ltr390_data *data;
+	struct iio_dev *indio_dev;
+	struct device *dev;
+	int ret, part_number;
+
+	dev = &client->dev;
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	data = iio_priv(indio_dev);
+
+	data->regmap = devm_regmap_init_i2c(client, &ltr390_regmap_config);
+	if (IS_ERR(data->regmap))
+		return dev_err_probe(dev, PTR_ERR(data->regmap),
+				     "regmap initialization failed\n");
+
+	data->client = client;
+	mutex_init(&data->lock);
+
+	indio_dev->info = &ltr390_info;
+	indio_dev->channels = &ltr390_channel;
+	indio_dev->num_channels = 1;
+	indio_dev->name = "ltr390";
+
+	ret = regmap_read(data->regmap, LTR390_PART_ID, &part_number);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "failed to get sensor's part id\n");
+	/* Lower 4 bits of `part_number` change with hardware revisions */
+	if (part_number >> 4 != LTR390_PART_NUMBER_ID)
+		dev_info(dev, "received invalid product id: 0x%x", part_number);
+	dev_dbg(dev, "LTR390, product id: 0x%x\n", part_number);
+
+	/* reset sensor, chip fails to respond to this, so ignore any errors */
+	regmap_set_bits(data->regmap, LTR390_MAIN_CTRL, LTR390_SW_RESET);
+
+	/* Wait for the registers to reset before proceeding */
+	usleep_range(1000, 2000);
+
+	ret = regmap_set_bits(data->regmap, LTR390_MAIN_CTRL,
+			      LTR390_SENSOR_ENABLE | LTR390_UVS_MODE);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to enable the sensor\n");
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct i2c_device_id ltr390_id[] = {
+	{ "ltr390" },
+	{ /* Sentinel */ }
+};
+MODULE_DEVICE_TABLE(i2c, ltr390_id);
+
+static const struct of_device_id ltr390_of_table[] = {
+	{ .compatible = "liteon,ltr390" },
+	{ /* Sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, ltr390_of_table);
+
+static struct i2c_driver ltr390_driver = {
+	.driver = {
+		.name = "ltr390",
+		.of_match_table = ltr390_of_table,
+	},
+	.probe = ltr390_probe,
+	.id_table = ltr390_id,
+};
+module_i2c_driver(ltr390_driver);
+
+MODULE_AUTHOR("Anshul Dalal <anshulusr@gmail.com>");
+MODULE_DESCRIPTION("Lite-On LTR390 ALS and UV sensor Driver");
+MODULE_LICENSE("GPL");