iio: adc: add ltc2309 support

The LTC2309 is an 8-Channel, 12-Bit SAR ADC with an I2C Interface.

This implements support for all single-ended and differential channels,
in unipolar mode only.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Link: https://lore.kernel.org/r/20230828-ltc2309-v3-2-338b3a8fab8b@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/Kconfig

@@ -607,6 +607,16 @@ config LPC32XX_ADC
 	  activate only one via device tree selection.  Provides direct access
 	  via sysfs.
 
+config LTC2309
+	tristate "Linear Technology LTC2309 ADC driver"
+	depends on I2C
+	help
+	  Say yes here to build support for Linear Technology LTC2309, a low
+	  noise, low power, 8-channel, 12-bit SAR ADC
+
+	  This driver can also be built as a module. If so, the module will
+	  be called ltc2309.
+
 config LTC2471
 	tristate "Linear Technology LTC2471 and LTC2473 ADC driver"
 	depends on I2C

drivers/iio/adc/Makefile

@@ -56,6 +56,7 @@ obj-$(CONFIG_INTEL_MRFLD_ADC) += intel_mrfld_adc.o
 obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
 obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
 obj-$(CONFIG_LPC32XX_ADC) += lpc32xx_adc.o
+obj-$(CONFIG_LTC2309) += ltc2309.o
 obj-$(CONFIG_LTC2471) += ltc2471.o
 obj-$(CONFIG_LTC2485) += ltc2485.o
 obj-$(CONFIG_LTC2496) += ltc2496.o ltc2497-core.o

drivers/iio/adc/ltc2309.c

@@ -0,0 +1,246 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * The LTC2309 is an 8-Channel, 12-Bit SAR ADC with an I2C Interface.
+ *
+ * Datasheet:
+ * https://www.analog.com/media/en/technical-documentation/data-sheets/2309fd.pdf
+ *
+ * Copyright (c) 2023, Liam Beguin <liambeguin@gmail.com>
+ */
+#include <linux/bitfield.h>
+#include <linux/i2c.h>
+#include <linux/iio/iio.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/regulator/consumer.h>
+
+#define LTC2309_ADC_RESOLUTION	12
+
+#define LTC2309_DIN_CH_MASK	GENMASK(7, 4)
+#define LTC2309_DIN_SDN		BIT(7)
+#define LTC2309_DIN_OSN		BIT(6)
+#define LTC2309_DIN_S1		BIT(5)
+#define LTC2309_DIN_S0		BIT(4)
+#define LTC2309_DIN_UNI		BIT(3)
+#define LTC2309_DIN_SLEEP	BIT(2)
+
+/**
+ * struct ltc2309 - internal device data structure
+ * @dev:	Device reference
+ * @client:	I2C reference
+ * @vref:	External reference source
+ * @lock:	Lock to serialize data access
+ * @vref_mv:	Internal voltage reference
+ */
+struct ltc2309 {
+	struct device		*dev;
+	struct i2c_client	*client;
+	struct regulator	*vref;
+	struct mutex		lock; /* serialize data access */
+	int			vref_mv;
+};
+
+/* Order matches expected channel address, See datasheet Table 1. */
+enum ltc2309_channels {
+	LTC2309_CH0_CH1 = 0,
+	LTC2309_CH2_CH3,
+	LTC2309_CH4_CH5,
+	LTC2309_CH6_CH7,
+	LTC2309_CH1_CH0,
+	LTC2309_CH3_CH2,
+	LTC2309_CH5_CH4,
+	LTC2309_CH7_CH6,
+	LTC2309_CH0,
+	LTC2309_CH2,
+	LTC2309_CH4,
+	LTC2309_CH6,
+	LTC2309_CH1,
+	LTC2309_CH3,
+	LTC2309_CH5,
+	LTC2309_CH7,
+};
+
+#define LTC2309_CHAN(_chan, _addr) {				\
+	.type = IIO_VOLTAGE,					\
+	.indexed = 1,						\
+	.address = _addr,					\
+	.channel = _chan,					\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
+}
+
+#define LTC2309_DIFF_CHAN(_chan, _chan2, _addr) {		\
+	.type = IIO_VOLTAGE,					\
+	.differential = 1,					\
+	.indexed = 1,						\
+	.address = _addr,					\
+	.channel = _chan,					\
+	.channel2 = _chan2,					\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
+}
+
+static const struct iio_chan_spec ltc2309_channels[] = {
+	LTC2309_CHAN(0, LTC2309_CH0),
+	LTC2309_CHAN(1, LTC2309_CH1),
+	LTC2309_CHAN(2, LTC2309_CH2),
+	LTC2309_CHAN(3, LTC2309_CH3),
+	LTC2309_CHAN(4, LTC2309_CH4),
+	LTC2309_CHAN(5, LTC2309_CH5),
+	LTC2309_CHAN(6, LTC2309_CH6),
+	LTC2309_CHAN(7, LTC2309_CH7),
+	LTC2309_DIFF_CHAN(0, 1, LTC2309_CH0_CH1),
+	LTC2309_DIFF_CHAN(2, 3, LTC2309_CH2_CH3),
+	LTC2309_DIFF_CHAN(4, 5, LTC2309_CH4_CH5),
+	LTC2309_DIFF_CHAN(6, 7, LTC2309_CH6_CH7),
+	LTC2309_DIFF_CHAN(1, 0, LTC2309_CH1_CH0),
+	LTC2309_DIFF_CHAN(3, 2, LTC2309_CH3_CH2),
+	LTC2309_DIFF_CHAN(5, 4, LTC2309_CH5_CH4),
+	LTC2309_DIFF_CHAN(7, 6, LTC2309_CH7_CH6),
+};
+
+static int ltc2309_read_raw_channel(struct ltc2309 *ltc2309,
+				    unsigned long address, int *val)
+{
+	int ret;
+	u16 buf;
+	u8 din;
+
+	din = FIELD_PREP(LTC2309_DIN_CH_MASK, address & 0x0f) |
+		FIELD_PREP(LTC2309_DIN_UNI, 1) |
+		FIELD_PREP(LTC2309_DIN_SLEEP, 0);
+
+	ret = i2c_smbus_write_byte(ltc2309->client, din);
+	if (ret < 0) {
+		dev_err(ltc2309->dev, "i2c command failed: %pe\n",
+			ERR_PTR(ret));
+		return ret;
+	}
+
+	ret = i2c_master_recv(ltc2309->client, (char *)&buf, 2);
+	if (ret < 0) {
+		dev_err(ltc2309->dev, "i2c read failed: %pe\n", ERR_PTR(ret));
+		return ret;
+	}
+
+	*val = be16_to_cpu(buf) >> 4;
+
+	return ret;
+}
+
+static int ltc2309_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan, int *val,
+			    int *val2, long mask)
+{
+	struct ltc2309 *ltc2309 = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		mutex_lock(&ltc2309->lock);
+		ret = ltc2309_read_raw_channel(ltc2309, chan->address, val);
+		mutex_unlock(&ltc2309->lock);
+		if (ret < 0)
+			return -EINVAL;
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		*val = ltc2309->vref_mv;
+		*val2 = LTC2309_ADC_RESOLUTION;
+		return IIO_VAL_FRACTIONAL_LOG2;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info ltc2309_info = {
+	.read_raw = ltc2309_read_raw,
+};
+
+static void ltc2309_regulator_disable(void *regulator)
+{
+	regulator_disable(regulator);
+}
+
+static int ltc2309_probe(struct i2c_client *client)
+{
+	struct iio_dev *indio_dev;
+	struct ltc2309 *ltc2309;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*ltc2309));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	ltc2309 = iio_priv(indio_dev);
+	ltc2309->dev = &indio_dev->dev;
+	ltc2309->client = client;
+	ltc2309->vref_mv = 4096; /* Default to the internal ref */
+
+	indio_dev->name = "ltc2309";
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = ltc2309_channels;
+	indio_dev->num_channels = ARRAY_SIZE(ltc2309_channels);
+	indio_dev->info = &ltc2309_info;
+
+	ltc2309->vref = devm_regulator_get_optional(&client->dev, "vref");
+	if (IS_ERR(ltc2309->vref)) {
+		ret = PTR_ERR(ltc2309->vref);
+		if (ret == -ENODEV)
+			ltc2309->vref = NULL;
+		else
+			return ret;
+	}
+
+	if (ltc2309->vref) {
+		ret = regulator_enable(ltc2309->vref);
+		if (ret)
+			return dev_err_probe(ltc2309->dev, ret,
+					     "failed to enable vref\n");
+
+		ret = devm_add_action_or_reset(ltc2309->dev,
+					       ltc2309_regulator_disable,
+					       ltc2309->vref);
+		if (ret) {
+			return dev_err_probe(ltc2309->dev, ret,
+					     "failed to add regulator_disable action: %d\n",
+					     ret);
+		}
+
+		ret = regulator_get_voltage(ltc2309->vref);
+		if (ret < 0)
+			return ret;
+
+		ltc2309->vref_mv = ret / 1000;
+	}
+
+	mutex_init(&ltc2309->lock);
+
+	return devm_iio_device_register(&client->dev, indio_dev);
+}
+
+static const struct of_device_id ltc2309_of_match[] = {
+	{ .compatible = "lltc,ltc2309" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ltc2309_of_match);
+
+static const struct i2c_device_id ltc2309_id[] = {
+	{ "ltc2309" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ltc2309_id);
+
+static struct i2c_driver ltc2309_driver = {
+	.driver = {
+		.name = "ltc2309",
+		.of_match_table = ltc2309_of_match,
+	},
+	.probe		= ltc2309_probe,
+	.id_table	= ltc2309_id,
+};
+module_i2c_driver(ltc2309_driver);
+
+MODULE_AUTHOR("Liam Beguin <liambeguin@gmail.com>");
+MODULE_DESCRIPTION("Linear Technology LTC2309 ADC");
+MODULE_LICENSE("GPL v2");