[PATCH] iio: potentiometer: add driver for Maxim Integrated DS1807

[Michael Trimarchi <michael@amarulasolutions.com>]

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

Value are exported in DBm because it's used as an audio
attenuator

Datasheet: https://datasheets.maximintegrated.com/en/ds/DS1807.pdf

Change-Id: I24f6b33cfa92ce16f489ff763f1df26126a1a7f2
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
---
 .../bindings/iio/potentiometer/ds1807.txt          |  17 +++
 drivers/iio/potentiometer/Kconfig                  |  10 ++
 drivers/iio/potentiometer/Makefile                 |   1 +
 drivers/iio/potentiometer/ds1807.c                 | 156 +++++++++++++++++++++
 4 files changed, 184 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/potentiometer/ds1807.txt
 create mode 100644 drivers/iio/potentiometer/ds1807.c

diff --git a/Documentation/devicetree/bindings/iio/potentiometer/ds1807.txt b/Documentation/devicetree/bindings/iio/potentiometer/ds1807.txt
new file mode 100644
index 0000000..3e30f4c
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/potentiometer/ds1807.txt
@@ -0,0 +1,17 @@
+* Maxim Integrated DS1807 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: "maxim,ds1807",
+
+Example:
+ds1807: ds1807@1 {
+	reg = <0x28>;
+	compatible = "maxim,ds1807";
+};
diff --git a/drivers/iio/potentiometer/Kconfig b/drivers/iio/potentiometer/Kconfig
index 79ec2eb..92e5a6b 100644
--- a/drivers/iio/potentiometer/Kconfig
+++ b/drivers/iio/potentiometer/Kconfig
@@ -25,6 +25,16 @@ config DS1803
 	  To compile this driver as a module, choose M here: the
 	  module will be called ds1803.
 
+config DS1807
+	tristate "Maxim Integrated DS1807 Digital Potentiometer driver"
+	depends on I2C
+	help
+	  Say yes here to build support for the Maxim Integrated DS1807
+	  digital potentiometer chip. Value are reported back in DBm
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ds1807.
+
 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 4af6578..3c409bb 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-$(CONFIG_DS1807) += ds1807.o
 obj-$(CONFIG_MAX5481) += max5481.o
 obj-$(CONFIG_MAX5487) += max5487.o
 obj-$(CONFIG_MCP4018) += mcp4018.o
diff --git a/drivers/iio/potentiometer/ds1807.c b/drivers/iio/potentiometer/ds1807.c
new file mode 100644
index 0000000..acb4884
--- /dev/null
+++ b/drivers/iio/potentiometer/ds1807.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Maxim Integrated DS1807 digital potentiometer driver
+ * Copyright (c) 2018 Michael Trimarchi
+ *
+ * Datasheet: https://datasheets.maximintegrated.com/en/ds/DS1807.pdf
+ *
+ * DEVID	#Wipers	#Positions	Resistor Opts (kOhm)	i2c address
+ * ds1807	2	65		45			0101xxx
+ *
+ */
+
+#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 DS1807_MAX_VALUE	64
+#define DS1807_MUTE		-90
+#define DS1807_WRITE(chan)	(0xa8 | ((chan) + 1))
+
+#define DS1807_CHANNEL(ch) {					\
+	.type = IIO_CHAN_INFO_HARDWAREGAIN,			\
+	.indexed = 1,						\
+	.output = 1,						\
+	.channel = (ch),					\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_HARDWAREGAIN),	\
+}
+
+static const struct iio_chan_spec ds1807_channels[] = {
+	DS1807_CHANNEL(0),
+	DS1807_CHANNEL(1),
+};
+
+struct ds1807_data {
+	struct i2c_client *client;
+};
+
+static int ds1807_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int *val, int *val2, long mask)
+{
+	struct ds1807_data *data = iio_priv(indio_dev);
+	int pot = chan->channel;
+	int ret;
+	u8 result[ARRAY_SIZE(ds1807_channels)];
+
+	switch (mask) {
+	case IIO_CHAN_INFO_HARDWAREGAIN:
+		ret = i2c_master_recv(data->client, result,
+				indio_dev->num_channels);
+		if (ret < 0)
+			return ret;
+
+		*val2 = 0;
+		if (result[pot] == DS1807_MAX_VALUE)
+			*val = DS1807_MUTE;
+		else
+			*val = -result[pot];
+
+		return IIO_VAL_INT_PLUS_MICRO_DB;
+	}
+
+	return -EINVAL;
+}
+
+static int ds1807_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     int val, int val2, long mask)
+{
+	struct ds1807_data *data = iio_priv(indio_dev);
+	int pot = chan->channel;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_HARDWAREGAIN:
+		if (val2 != 0 || val < DS1807_MUTE || val > 0)
+			return -EINVAL;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	val = (val == DS1807_MUTE) ? DS1807_MAX_VALUE : -val;
+
+	return i2c_smbus_write_byte_data(data->client, DS1807_WRITE(pot), val);
+}
+
+static const struct iio_info ds1807_info = {
+	.read_raw = ds1807_read_raw,
+	.write_raw = ds1807_write_raw,
+};
+
+static int ds1807_probe(struct i2c_client *client,
+			 const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct ds1807_data *data;
+	struct iio_dev *indio_dev;
+	int channel, ret;
+
+	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;
+
+	indio_dev->dev.parent = dev;
+	indio_dev->info = &ds1807_info;
+	indio_dev->channels = ds1807_channels;
+	indio_dev->num_channels = ARRAY_SIZE(ds1807_channels);
+	indio_dev->name = client->name;
+
+	/* reset device gain */
+	for (channel = 0; channel < indio_dev->num_channels; channel++) {
+		ret = i2c_smbus_write_byte_data(client, DS1807_WRITE(channel),
+						DS1807_MUTE);
+		if (ret < 0)
+			return -ENODEV;
+	}
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+#if defined(CONFIG_OF)
+static const struct of_device_id ds1807_dt_ids[] = {
+	{ .compatible = "maxim,ds1807", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, ds1807_dt_ids);
+#endif /* CONFIG_OF */
+
+static const struct i2c_device_id ds1807_id[] = {
+	{ "ds1807", },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, ds1807_id);
+
+static struct i2c_driver ds1807_driver = {
+	.driver = {
+		.name	= "ds1807",
+		.of_match_table = of_match_ptr(ds1807_dt_ids),
+	},
+	.probe		= ds1807_probe,
+	.id_table	= ds1807_id,
+};
+
+module_i2c_driver(ds1807_driver);
+
+MODULE_AUTHOR("Michael Trimarchi <michael@amarulasolutions.com>");
+MODULE_DESCRIPTION("DS1807 digital potentiometer");
+MODULE_LICENSE("GPL v2");
-- 
2.7.4