iio: potentiometer: add driver for Maxim Integrated DS1803

The following functions are supported:
- write, read potentiometer value
- potentiometer scale

Datasheet: https://datasheets.maximintegrated.com/en/ds/DS1803.pdf

Signed-off-by Slawomir Stepien <[email protected]>

---
 .../bindings/iio/potentiometer/ds1803.txt          |  21 +++
 drivers/iio/potentiometer/Kconfig                  |  10 ++
 drivers/iio/potentiometer/Makefile                 |   1 +
 drivers/iio/potentiometer/ds1803.c                 | 178 +++++++++++++++++++++
 4 files changed, 210 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/potentiometer/ds1803.txt
 create mode 100644 drivers/iio/potentiometer/ds1803.c

Documentation/devicetree/bindings/iio/potentiometer/ds1803.txt new file +21 -0

new file mode 100644
index 0000000..df77bf5
@@ -0,0 +1,21 @@
+* Maxim Integrated DS1803 digital potentiometer driver
+
+The node for this driver must be a child node of a I2C controller, hence
+all mandatory properties for your controller must be specified. See directory:
+
+        Documentation/devicetree/bindings/i2c
+
+for more details.
+
+Required properties:
+	- compatible:  	Must be one of the following, depending on the
+			model:
+			"maxim,ds1803-010",
+			"maxim,ds1803-050",
+			"maxim,ds1803-100"
+
+Example:
+ds1803: ds1803@1 {
+	reg = <0x28>;
+	compatible = "maxim,ds1803-010";
+};

drivers/iio/potentiometer/Kconfig +10 -0

index 7ea069b..6acb238 100644
@@ -5,6 +5,16 @@
 
 menu "Digital potentiometers"
 
+config DS1803
+	tristate "Maxim Integrated DS1803 Digital Potentiometer driver"
+	depends on I2C
+	help
+	  Say yes here to build support for the Maxim Integrated DS1803
+	  digital potentiomenter chip.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ds1803.
+
 config MCP4131
 	tristate "Microchip MCP413X/414X/415X/416X/423X/424X/425X/426X Digital Potentiometer driver"
 	depends on SPI

drivers/iio/potentiometer/Makefile +1 -0

index 91a80f8..6007faa 100644
@@ -3,6 +3,7 @@
 #
 
 # When adding new entries keep the list in alphabetical order
+obj-$(CONFIG_DS1803) += ds1803.o
 obj-$(CONFIG_MCP4131) += mcp4131.o
 obj-$(CONFIG_MCP4531) += mcp4531.o
 obj-$(CONFIG_TPL0102) += tpl0102.o

drivers/iio/potentiometer/ds1803.c new file +5 -0

new file mode 100644
index 0000000..b5e5b1c
@@ -0,0 +1,178 @@
+/*
+ * Maxim Integrated DS1803 digital potentiometer driver
+ * Copyright (c) 2016 Slawomir Stepien
+ *
+ * Datasheet: https://datasheets.maximintegrated.com/en/ds/DS1803.pdf

drivers/iio/potentiometer/ds1803.c new file +47 -0

+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/i2c.h>
+#include <linux/iio/iio.h>
+#include <linux/module.h>
+#include <linux/of.h>
+
+#define DS1803_NUM_WIPERS	2
+#define DS1803_MAX_POS		255
+#define DS1803_WRITE(n)		(0xA8 | ((n) + 1))
+
+enum ds1803_type {
+	DS1803_010,
+	DS1803_050,
+	DS1803_100,
+};
+
+struct ds1803_cfg {
+	int kohms;
+};
+
+static const struct ds1803_cfg ds1803_cfg[] = {
+	[DS1803_010] = { .kohms =  10, },
+	[DS1803_050] = { .kohms =  50, },
+	[DS1803_100] = { .kohms = 100, },
+};
+
+struct ds1803_data {
+	struct i2c_client *client;
+	const struct ds1803_cfg *cfg;
+};
+
+#define DS1803_CHANNEL(ch) {					\
+	.type = IIO_RESISTANCE,					\
+	.indexed = 1,						\
+	.output = 1,						\
+	.channel = (ch),					\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
+}
+
+static const struct iio_chan_spec ds1803_channels[] = {
+	DS1803_CHANNEL(0),
+	DS1803_CHANNEL(1),
+};
+
+static int ds1803_read_raw(struct iio_dev *indio_dev,

drivers/iio/potentiometer/ds1803.c new file +11 -0

+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		*val = 1000 * data->cfg->kohms;
+		*val2 = DS1803_MAX_POS;
+		return IIO_VAL_FRACTIONAL;
+	}
+
+	return -EINVAL;
+}
+

drivers/iio/potentiometer/ds1803.c new file +33 -0

+			return -EINVAL;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return i2c_smbus_write_byte_data(data->client, DS1803_WRITE(pot), val);
+}
+
+static const struct iio_info ds1803_info = {
+	.read_raw = ds1803_read_raw,
+	.write_raw = ds1803_write_raw,
+	.driver_module = THIS_MODULE,
+};
+
+static int ds1803_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct ds1803_data *data;
+	struct iio_dev *indio_dev;
+
+	/* Value of two pots is read at the same time */
+	if (!i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_WORD_DATA)) {
+		dev_err(dev, "SMBUS Word Data not supported\n");
+		return -EOPNOTSUPP;
+	}
+
+	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+

drivers/iio/potentiometer/ds1803.c new file +37 -0

+	indio_dev->name = client->name;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+#if defined(CONFIG_OF)
+static const struct of_device_id ds1803_dt_ids[] = {
+	{ .compatible = "maxim,ds1803-010", .data = &ds1803_cfg[DS1803_010] },
+	{ .compatible = "maxim,ds1803-050", .data = &ds1803_cfg[DS1803_050] },
+	{ .compatible = "maxim,ds1803-100", .data = &ds1803_cfg[DS1803_100] },
+	{}
+};
+MODULE_DEVICE_TABLE(of, ds1803_dt_ids);
+#endif /* CONFIG_OF */
+
+static const struct i2c_device_id ds1803_id[] = {
+	{ "ds1803-010", DS1803_010 },
+	{ "ds1803-050", DS1803_050 },
+	{ "ds1803-100", DS1803_100 },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, ds1803_id);
+
+static struct i2c_driver ds1803_driver = {
+	.driver = {
+		.name	= "ds1803",
+		.of_match_table = of_match_ptr(ds1803_dt_ids),
+	},
+	.probe		= ds1803_probe,
+	.id_table	= ds1803_id,
+};
+
+module_i2c_driver(ds1803_driver);
+
+MODULE_AUTHOR("Slawomir Stepien <[email protected]>");
+MODULE_DESCRIPTION("DS1803 digital potentiometer");
+MODULE_LICENSE("GPL v2");

Quoted 4 lines

The following functions are supported:
- write, read potentiometer value
- potentiometer scale

minor comments below, nice driver

Quoted 1 line

+#include <linux/cache.h>

for what is cache.h needed?

Quoted 5 lines

drivers/iio/potentiometer/ds1803.c new file +5 -0

+static int ds1803_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int *val, int *val2, long mask)
+{
+	struct ds1803_data *data = iio_priv(indio_dev);

drivers/iio/potentiometer/ds1803.c line 72

Quoted 6 lines

drivers/iio/potentiometer/ds1803.c new file +6 -0

+	int pot = chan->channel;
+	s32 ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = i2c_smbus_read_word_swapped(data->client, 0);

maybe a #define to explain the name of register 0

drivers/iio/potentiometer/ds1803.c line 77

Quoted 5 lines

drivers/iio/potentiometer/ds1803.c new file +5 -0

+		if (ret < 0)
+			return ret;
+
+		/* Get bits for given pot */
+		*val = (pot == 0 ? ret >> 8 : ret & 255);

often 0xff is used to mask a byte

Quoted 15 lines

drivers/iio/potentiometer/ds1803.c new file +15 -0

+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		*val = 1000 * data->cfg->kohms;
+		*val2 = DS1803_MAX_POS;
+		return IIO_VAL_FRACTIONAL;
+	}
+
+	return -EINVAL;
+}
+
+static int ds1803_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     int val, int val2, long mask)
+{

drivers/iio/potentiometer/ds1803.c line 98

Quoted 6 lines

drivers/iio/potentiometer/ds1803.c new file +6 -0

+	struct ds1803_data *data = iio_priv(indio_dev);
+	int pot = chan->channel;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		if (val > DS1803_MAX_POS || val < 0)

check that val2 is 0 or use .write_raw_get_fmt

drivers/iio/potentiometer/ds1803.c line 141

Quoted 4 lines

drivers/iio/potentiometer/ds1803.c new file +4 -0

+	indio_dev->dev.parent = dev;
+	indio_dev->info = &ds1803_info;
+	indio_dev->channels = ds1803_channels;
+	indio_dev->num_channels = DS1803_NUM_WIPERS;

ARRAY_SIZE(ds1803_channels)

Quoted 2 lines

maybe a #define to explain the name of register 0

Well this zero is not register nor any kind of command that DS1803 needs to send back pots values.
DS1803 only requires the standard R/W bit to be set as read.
I used _word_ function series to get back a word (16 bits) as this poti returns 16 bits.

How should I named it?

#define NON_COMMAND 0
?

Or should I use different function? (2x i2c_smbus_read_byte?)

The i2c_smbus_read_byte() function also used 0 as command for its transfers...

Quoted 4 lines

Quoted 4 lines

drivers/iio/potentiometer/ds1803.c new file +4 -0

+static int ds1803_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     int val, int val2, long mask)
+{

Quoted 8 lines

drivers/iio/potentiometer/ds1803.c line 98

Quoted 6 lines

drivers/iio/potentiometer/ds1803.c new file +6 -0

+	struct ds1803_data *data = iio_priv(indio_dev);
+	int pot = chan->channel;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		if (val > DS1803_MAX_POS || val < 0)

check that val2 is 0 or use .write_raw_get_fmt

At this point I do not know why should I do it, but I will look into that.

Quoted 9 lines

Quoted 2 lines

maybe a #define to explain the name of register 0

Well this zero is not register nor any kind of command that DS1803 needs to send back pots values.
DS1803 only requires the standard R/W bit to be set as read.
I used _word_ function series to get back a word (16 bits) as this poti returns 16 bits.

Quoted 4 lines

How should I named it?

#define NON_COMMAND 0
?

maybe i2c_transfer() is more appropriate then

        u8 databuf[2];
        struct i2c_msg msgs[2] = {
                { .addr = client->addr, .len = sizeof(databuf), .buf = databuf,
                  .flags = I2C_M_RD } };
        ret = i2c_transfer(client->adapter, msgs, 2);

this does not send any data to the chip but only reads two bytes

Quoted 18 lines

Or should I use different function? (2x i2c_smbus_read_byte?)

The i2c_smbus_read_byte() function also used 0 as command for its transfers...

Quoted 12 lines

drivers/iio/potentiometer/ds1803.c line 98

Quoted 10 lines

drivers/iio/potentiometer/ds1803.c new file +10 -0

+static int ds1803_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     int val, int val2, long mask)
+{
+	struct ds1803_data *data = iio_priv(indio_dev);
+	int pot = chan->channel;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		if (val > DS1803_MAX_POS || val < 0)

check that val2 is 0 or use .write_raw_get_fmt

Quoted 1 line

At this point I do not know why should I do it, but I will look into that.

write_raw expects a VAL_INT_PLUS_MICROS per default, passed in val and val2

you can change that with .write_raw_get_fmt (e.g. to expect VAL_INT), or just make sure that the micros are 0