iio: adc: Add MAX1241 driver

Add driver for the Maxim MAX1241 12-bit, single-channel ADC.

Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX1240-MAX1241.pdf
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Alexandru Lazar <alazar@startmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/Kconfig

@@ -630,6 +630,16 @@ config MAX1118
 	  To compile this driver as a module, choose M here: the module will be
 	  called max1118.
 
+config MAX1241
+	tristate "Maxim max1241 ADC driver"
+	depends on SPI_MASTER
+	help
+	  Say yes here to build support for Maxim max1241 12-bit, single-channel
+	  ADC.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called max1241.
+
 config MAX1363
 	tristate "Maxim max1363 ADC driver"
 	depends on I2C

drivers/iio/adc/Makefile

@@ -59,6 +59,7 @@ obj-$(CONFIG_LTC2497) += ltc2497.o ltc2497-core.o
 obj-$(CONFIG_MAX1027) += max1027.o
 obj-$(CONFIG_MAX11100) += max11100.o
 obj-$(CONFIG_MAX1118) += max1118.o
+obj-$(CONFIG_MAX1241) += max1241.o
 obj-$(CONFIG_MAX1363) += max1363.o
 obj-$(CONFIG_MAX9611) += max9611.o
 obj-$(CONFIG_MCP320X) += mcp320x.o

drivers/iio/adc/max1241.c

@@ -0,0 +1,227 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * MAX1241 low-power, 12-bit serial ADC
+ *
+ * Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX1240-MAX1241.pdf
+ */
+
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
+#include <linux/iio/iio.h>
+#include <linux/module.h>
+#include <linux/regulator/consumer.h>
+#include <linux/spi/spi.h>
+
+#define MAX1241_VAL_MASK GENMASK(11, 0)
+#define MAX1241_SHUTDOWN_DELAY_USEC 4
+
+enum max1241_id {
+	max1241,
+};
+
+struct max1241 {
+	struct spi_device *spi;
+	struct mutex lock;
+	struct regulator *vdd;
+	struct regulator *vref;
+	struct gpio_desc *shutdown;
+
+	__be16 data ____cacheline_aligned;
+};
+
+static const struct iio_chan_spec max1241_channels[] = {
+	{
+		.type = IIO_VOLTAGE,
+		.indexed = 1,
+		.channel = 0,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				BIT(IIO_CHAN_INFO_SCALE),
+	},
+};
+
+static int max1241_read(struct max1241 *adc)
+{
+	struct spi_transfer xfers[] = {
+		/*
+		 * Begin conversion by bringing /CS low for at least
+		 * tconv us.
+		 */
+		{
+			.len = 0,
+			.delay.value = 8,
+			.delay.unit = SPI_DELAY_UNIT_USECS,
+		},
+		/*
+		 * Then read two bytes of data in our RX buffer.
+		 */
+		{
+			.rx_buf = &adc->data,
+			.len = 2,
+		},
+	};
+
+	return spi_sync_transfer(adc->spi, xfers, ARRAY_SIZE(xfers));
+}
+
+static int max1241_read_raw(struct iio_dev *indio_dev,
+			struct iio_chan_spec const *chan,
+			int *val, int *val2, long mask)
+{
+	int ret, vref_uV;
+	struct max1241 *adc = iio_priv(indio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		mutex_lock(&adc->lock);
+
+		if (adc->shutdown) {
+			gpiod_set_value(adc->shutdown, 0);
+			udelay(MAX1241_SHUTDOWN_DELAY_USEC);
+			ret = max1241_read(adc);
+			gpiod_set_value(adc->shutdown, 1);
+		} else
+			ret = max1241_read(adc);
+
+		if (ret) {
+			mutex_unlock(&adc->lock);
+			return ret;
+		}
+
+		*val = (be16_to_cpu(adc->data) >> 3) & MAX1241_VAL_MASK;
+
+		mutex_unlock(&adc->lock);
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SCALE:
+		vref_uV = regulator_get_voltage(adc->vref);
+
+		if (vref_uV < 0)
+			return vref_uV;
+
+		*val = vref_uV / 1000;
+		*val2 = 12;
+
+		return IIO_VAL_FRACTIONAL_LOG2;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info max1241_info = {
+	.read_raw = max1241_read_raw,
+};
+
+static void max1241_disable_vdd_action(void *data)
+{
+	struct max1241 *adc = data;
+	struct device *dev = &adc->spi->dev;
+	int err;
+
+	err = regulator_disable(adc->vdd);
+	if (err)
+		dev_err(dev, "could not disable vdd regulator.\n");
+}
+
+static void max1241_disable_vref_action(void *data)
+{
+	struct max1241 *adc = data;
+	struct device *dev = &adc->spi->dev;
+	int err;
+
+	err = regulator_disable(adc->vref);
+	if (err)
+		dev_err(dev, "could not disable vref regulator.\n");
+}
+
+static int max1241_probe(struct spi_device *spi)
+{
+	struct device *dev = &spi->dev;
+	struct iio_dev *indio_dev;
+	struct max1241 *adc;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*adc));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	adc = iio_priv(indio_dev);
+	adc->spi = spi;
+	mutex_init(&adc->lock);
+
+	spi_set_drvdata(spi, indio_dev);
+
+	adc->vdd = devm_regulator_get(dev, "vdd");
+	if (IS_ERR(adc->vdd)) {
+		dev_err(dev, "failed to get vdd regulator\n");
+		return PTR_ERR(adc->vdd);
+	}
+
+	ret = regulator_enable(adc->vdd);
+	if (ret)
+		return ret;
+
+	ret = devm_add_action_or_reset(dev, max1241_disable_vdd_action, adc);
+	if (ret) {
+		dev_err(dev, "could not set up vdd regulator cleanup action\n");
+		return ret;
+	}
+
+	adc->vref = devm_regulator_get(dev, "vref");
+	if (IS_ERR(adc->vref)) {
+		dev_err(dev, "failed to get vref regulator\n");
+		return PTR_ERR(adc->vref);
+	}
+
+	ret = regulator_enable(adc->vref);
+	if (ret)
+		return ret;
+
+	ret = devm_add_action_or_reset(dev, max1241_disable_vref_action, adc);
+	if (ret) {
+		dev_err(dev, "could not set up vref regulator cleanup action\n");
+		return ret;
+	}
+
+	adc->shutdown = devm_gpiod_get_optional(dev, "shutdown",
+						GPIOD_OUT_HIGH);
+	if (IS_ERR(adc->shutdown))
+		return PTR_ERR(adc->shutdown);
+
+	if (adc->shutdown)
+		dev_dbg(dev, "shutdown pin passed, low-power mode enabled");
+	else
+		dev_dbg(dev, "no shutdown pin passed, low-power mode disabled");
+
+	indio_dev->name = spi_get_device_id(spi)->name;
+	indio_dev->dev.parent = dev;
+	indio_dev->info = &max1241_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+	indio_dev->channels = max1241_channels;
+	indio_dev->num_channels = ARRAY_SIZE(max1241_channels);
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct spi_device_id max1241_id[] = {
+	{ "max1241", max1241 },
+	{}
+};
+
+static const struct of_device_id max1241_dt_ids[] = {
+	{ .compatible = "maxim,max1241" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, max1241_dt_ids);
+
+static struct spi_driver max1241_spi_driver = {
+	.driver = {
+		.name = "max1241",
+		.of_match_table = max1241_dt_ids,
+	},
+	.probe = max1241_probe,
+	.id_table = max1241_id,
+};
+module_spi_driver(max1241_spi_driver);
+
+MODULE_AUTHOR("Alexandru Lazar <alazar@startmail.com>");
+MODULE_DESCRIPTION("MAX1241 ADC driver");
+MODULE_LICENSE("GPL v2");