[PATCH v4 1/2] iio: potentiometer: add a driver for Maxim 5432-5435

[Martin Kaiser <martin@kaiser.cx>]

Add a driver for the Maxim Integrated MAX5432-MAX5435 family of digital
potentiometers.

These potentiometers are connected via I2C and have 32 wiper
positions.

Supported functionality
- set the volatile wiper position
- read the potentiometer scale

Datasheet:
https://datasheets.maximintegrated.com/en/ds/MAX5432-MAX5435.pdf

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
---
changes in v4
 - fix the dt bindings
   - replace ic20 with i2c
   - document the reg property
   - add additionalProperties and required

changes in v3
 - split dt bindings and driver code into separate patches
 - use yaml format for dt bindings
 - fix formatting of parameter lists

changes in v2
 - use MAX5432_ prefix for all defines
 - fix indentation
 - convert void * to unsigned long, not to u32
   (warning from kbuild test robot)

 drivers/iio/potentiometer/Kconfig   |  11 +++
 drivers/iio/potentiometer/Makefile  |   1 +
 drivers/iio/potentiometer/max5432.c | 135 ++++++++++++++++++++++++++++++++++++
 3 files changed, 147 insertions(+)
 create mode 100644 drivers/iio/potentiometer/max5432.c

diff --git a/drivers/iio/potentiometer/Kconfig b/drivers/iio/potentiometer/Kconfig
index ebc7c72a5e36..4cac0173db8b 100644
--- a/drivers/iio/potentiometer/Kconfig
+++ b/drivers/iio/potentiometer/Kconfig
@@ -26,6 +26,17 @@ config DS1803
 	  To compile this driver as a module, choose M here: the
 	  module will be called ds1803.
 
+config MAX5432
+	tristate "Maxim MAX5432-MAX5435 Digital Potentiometer driver"
+	depends on I2C
+	help
+	  Say yes here to build support for the Maxim
+	  MAX5432, MAX5433, MAX5434 and MAX5435 digital
+	  potentiometer chips.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called max5432.
+
 config MAX5481
 	tristate "Maxim MAX5481-MAX5484 Digital Potentiometer driver"
 	depends on SPI
diff --git a/drivers/iio/potentiometer/Makefile b/drivers/iio/potentiometer/Makefile
index 8ff55138cf12..091adf3cdd0b 100644
--- a/drivers/iio/potentiometer/Makefile
+++ b/drivers/iio/potentiometer/Makefile
@@ -6,6 +6,7 @@
 # When adding new entries keep the list in alphabetical order
 obj-$(CONFIG_AD5272) += ad5272.o
 obj-$(CONFIG_DS1803) += ds1803.o
+obj-$(CONFIG_MAX5432) += max5432.o
 obj-$(CONFIG_MAX5481) += max5481.o
 obj-$(CONFIG_MAX5487) += max5487.o
 obj-$(CONFIG_MCP4018) += mcp4018.o
diff --git a/drivers/iio/potentiometer/max5432.c b/drivers/iio/potentiometer/max5432.c
new file mode 100644
index 000000000000..641b1821fdf6
--- /dev/null
+++ b/drivers/iio/potentiometer/max5432.c
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Maxim Integrated MAX5432-MAX5435 digital potentiometer driver
+ * Copyright (C) 2019 Martin Kaiser <martin@kaiser.cx>
+ *
+ * Datasheet:
+ * https://datasheets.maximintegrated.com/en/ds/MAX5432-MAX5435.pdf
+ */
+
+#include <linux/i2c.h>
+#include <linux/iio/iio.h>
+#include <linux/limits.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+
+/* All chip variants have 32 wiper positions. */
+#define MAX5432_MAX_POS 31
+
+#define MAX5432_OHM_50K   (50  * 1000)
+#define MAX5432_OHM_100K  (100 * 1000)
+
+/* Update the volatile (currently active) setting. */
+#define MAX5432_CMD_VREG  0x11
+
+struct max5432_data {
+	struct i2c_client *client;
+	unsigned long ohm;
+};
+
+static const struct iio_chan_spec max5432_channels[] = {
+	{
+		.type = IIO_RESISTANCE,
+		.indexed = 1,
+		.output = 1,
+		.channel = 0,
+		.address = MAX5432_CMD_VREG,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
+	}
+};
+
+static int max5432_read_raw(struct iio_dev *indio_dev,
+			struct iio_chan_spec const *chan,
+			int *val, int *val2, long mask)
+{
+	struct max5432_data *data = iio_priv(indio_dev);
+
+	if (mask != IIO_CHAN_INFO_SCALE)
+		return -EINVAL;
+
+	if (unlikely(data->ohm > INT_MAX))
+		return -ERANGE;
+
+	*val = data->ohm;
+	*val2 = MAX5432_MAX_POS;
+
+	return IIO_VAL_FRACTIONAL;
+}
+
+static int max5432_write_raw(struct iio_dev *indio_dev,
+			struct iio_chan_spec const *chan,
+			int val, int val2, long mask)
+{
+	struct max5432_data *data = iio_priv(indio_dev);
+	u8 data_byte;
+
+	if (mask != IIO_CHAN_INFO_RAW)
+		return -EINVAL;
+
+	if (val < 0 || val > MAX5432_MAX_POS)
+		return -EINVAL;
+
+	if (val2 != 0)
+		return -EINVAL;
+
+	/* Wiper position is in bits D7-D3. (D2-D0 are don't care bits.) */
+	data_byte = val << 3;
+	return i2c_smbus_write_byte_data(data->client, chan->address,
+			data_byte);
+}
+
+static const struct iio_info max5432_info = {
+	.read_raw = max5432_read_raw,
+	.write_raw = max5432_write_raw,
+};
+
+static int max5432_probe(struct i2c_client *client,
+		const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct iio_dev *indio_dev;
+	struct max5432_data *data;
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(struct max5432_data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	i2c_set_clientdata(client, indio_dev);
+
+	data = iio_priv(indio_dev);
+	data->client = client;
+	data->ohm = (unsigned long)of_device_get_match_data(dev);
+
+	indio_dev->dev.parent = dev;
+	indio_dev->info = &max5432_info;
+	indio_dev->channels = max5432_channels;
+	indio_dev->num_channels = ARRAY_SIZE(max5432_channels);
+	indio_dev->name = client->name;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct of_device_id max5432_dt_ids[] = {
+	{ .compatible = "maxim,max5432", .data = (void *)MAX5432_OHM_50K  },
+	{ .compatible = "maxim,max5433", .data = (void *)MAX5432_OHM_100K },
+	{ .compatible = "maxim,max5434", .data = (void *)MAX5432_OHM_50K  },
+	{ .compatible = "maxim,max5435", .data = (void *)MAX5432_OHM_100K },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, max5432_dt_ids);
+
+static struct i2c_driver max5432_driver = {
+	.driver = {
+		.name = "max5432",
+		.of_match_table = of_match_ptr(max5432_dt_ids),
+	},
+	.probe = max5432_probe,
+};
+
+module_i2c_driver(max5432_driver);
+
+MODULE_AUTHOR("Martin Kaiser <martin@kaiser.cx>");
+MODULE_DESCRIPTION("max5432-max5435 digital potentiometers");
+MODULE_LICENSE("GPL v2");
-- 
2.11.0