[PATCH] iio: potentiometer: add driver for Maxim Integrated DS1803

[PATCH] iio: potentiometer: add driver for Maxim Integrated DS1803

[Slawomir Stepien]

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 <sst@poczta.fm>
---
 .../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

diff --git a/Documentation/devicetree/bindings/iio/potentiometer/ds1803.txt b/Documentation/devicetree/bindings/iio/potentiometer/ds1803.txt
new file mode 100644
index 0000000..df77bf5
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/potentiometer/ds1803.txt
@@ -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";
+};
diff --git a/drivers/iio/potentiometer/Kconfig b/drivers/iio/potentiometer/Kconfig
index 7ea069b..6acb238 100644
--- a/drivers/iio/potentiometer/Kconfig
+++ b/drivers/iio/potentiometer/Kconfig
@@ -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
diff --git a/drivers/iio/potentiometer/Makefile b/drivers/iio/potentiometer/Makefile
index 91a80f8..6007faa 100644
--- a/drivers/iio/potentiometer/Makefile
+++ b/drivers/iio/potentiometer/Makefile
@@ -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
diff --git a/drivers/iio/potentiometer/ds1803.c b/drivers/iio/potentiometer/ds1803.c
new file mode 100644
index 0000000..b5e5b1c
--- /dev/null
+++ b/drivers/iio/potentiometer/ds1803.c
@@ -0,0 +1,178 @@
+/*
+ * Maxim Integrated DS1803 digital potentiometer driver
+ * Copyright (c) 2016 Slawomir Stepien
+ *
+ * Datasheet: https://datasheets.maximintegrated.com/en/ds/DS1803.pdf
+ *
+ * DEVID	#Wipers	#Positions	Resistor Opts (kOhm)	i2c address
+ * ds1803	2	256		10, 50, 100		0101xxx
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ */
+
+#include <linux/cache.h>
+#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,
+			    struct iio_chan_spec const *chan,
+			    int *val, int *val2, long mask)
+{
+	struct ds1803_data *data = iio_priv(indio_dev);
+	int pot = chan->channel;
+	s32 ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		ret = i2c_smbus_read_word_swapped(data->client, 0);
+		if (ret < 0)
+			return ret;
+
+		/* Get bits for given pot */
+		*val = (pot == 0 ? ret >> 8 : ret & 255);
+		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)
+{
+	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)
+			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;
+
+	i2c_set_clientdata(client, indio_dev);
+
+	data = iio_priv(indio_dev);
+	data->client = client;
+	data->cfg = &ds1803_cfg[id->driver_data];
+
+	indio_dev->dev.parent = dev;
+	indio_dev->info = &ds1803_info;
+	indio_dev->channels = ds1803_channels;
+	indio_dev->num_channels = DS1803_NUM_WIPERS;
+	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 <sst@poczta.fm>");
+MODULE_DESCRIPTION("DS1803 digital potentiometer");
+MODULE_LICENSE("GPL v2");
-- 
2.7.4

Re: [PATCH] iio: potentiometer: add driver for Maxim Integrated DS1803

[Peter Meerwald-Stadler]

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

minor comments below, nice driver
 
> Datasheet: https://datasheets.maximintegrated.com/en/ds/DS1803.pdf
> 
> Signed-off-by: Slawomir Stepien <sst@poczta.fm>
> ---
>  .../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
> 
> diff --git a/Documentation/devicetree/bindings/iio/potentiometer/ds1803.txt b/Documentation/devicetree/bindings/iio/potentiometer/ds1803.txt
> new file mode 100644
> index 0000000..df77bf5
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/potentiometer/ds1803.txt
> @@ -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";
> +};
> diff --git a/drivers/iio/potentiometer/Kconfig b/drivers/iio/potentiometer/Kconfig
> index 7ea069b..6acb238 100644
> --- a/drivers/iio/potentiometer/Kconfig
> +++ b/drivers/iio/potentiometer/Kconfig
> @@ -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
> diff --git a/drivers/iio/potentiometer/Makefile b/drivers/iio/potentiometer/Makefile
> index 91a80f8..6007faa 100644
> --- a/drivers/iio/potentiometer/Makefile
> +++ b/drivers/iio/potentiometer/Makefile
> @@ -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
> diff --git a/drivers/iio/potentiometer/ds1803.c b/drivers/iio/potentiometer/ds1803.c
> new file mode 100644
> index 0000000..b5e5b1c
> --- /dev/null
> +++ b/drivers/iio/potentiometer/ds1803.c
> @@ -0,0 +1,178 @@
> +/*
> + * Maxim Integrated DS1803 digital potentiometer driver
> + * Copyright (c) 2016 Slawomir Stepien
> + *
> + * Datasheet: https://datasheets.maximintegrated.com/en/ds/DS1803.pdf
> + *
> + * DEVID	#Wipers	#Positions	Resistor Opts (kOhm)	i2c address
> + * ds1803	2	256		10, 50, 100		0101xxx
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published by
> + * the Free Software Foundation.
> + */
> +
> +#include <linux/cache.h>

for what is cache.h needed?

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

> +		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

> +		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)
> +{
> +	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

> +			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;
> +
> +	i2c_set_clientdata(client, indio_dev);
> +
> +	data = iio_priv(indio_dev);
> +	data->client = client;
> +	data->cfg = &ds1803_cfg[id->driver_data];
> +
> +	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)

> +	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 <sst@poczta.fm>");
> +MODULE_DESCRIPTION("DS1803 digital potentiometer");
> +MODULE_LICENSE("GPL v2");
> 

-- 

Peter Meerwald-Stadler
+43-664-2444418 (mobile)

Re: [PATCH] iio: potentiometer: add driver for Maxim Integrated DS1803

[Slawomir Stepien]

On Apr 07, 2016 21:36, Peter Meerwald-Stadler wrote:
> 
> > The following functions are supported:
> >  - write, read potentiometer value
> >  - potentiometer scale
> 
> minor comments below, nice driver

Thank you for your comments!

> > +#include <linux/cache.h>
> 
> for what is cache.h needed?

It is not needed here. I will delete it in v2.

> > +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);
> > +	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

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...

> > +		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

OK.

> > +		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)
> > +{
> > +	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.

> > +	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)

Good point.

-- 
Slawomir Stepien

Re: [PATCH] iio: potentiometer: add driver for Maxim Integrated DS1803

[Peter Meerwald-Stadler]

> > 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
> ?

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
 
> 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...

> > > +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
> 
> 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
 
-- 

Peter Meerwald-Stadler
+43-664-2444418 (mobile)

Re: [PATCH] iio: potentiometer: add driver for Maxim Integrated DS1803

[Slawomir Stepien]

On Apr 08, 2016 18:00, Peter Meerwald-Stadler wrote:
> 
> > > 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
> > ?
> 
> 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

Good point. But maybe the better solution would be to use i2c_master_recv?
Anyhow I will check both options ;)

> > 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...
> 
> > > > +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
> > 
> > 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

Thank you for the explanation.

-- 
Slawomir Stepien