iio: max5481: Add support for Maxim digital potentiometers

Add implementation for Maxim Integrated 5481, 5482, 5483,
and 5484 digital potentiometer devices.

Datasheet:
http://datasheets.maximintegrated.com/en/ds/MAX5481-MAX5484.pdf

Signed-off-by: Maury Anderson <[e-mail]>
Signed-off-by: Matthew Weber <[e-mail]>
Signed-off-by: Slawomir Stepien <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/devicetree/bindings/iio/potentiometer/max5481.txt

···
+* Maxim Linear-Taper Digital Potentiometer MAX5481-MAX5484
+
+The node for this driver must be a child node of a SPI controller, hence
+all mandatory properties described in
+
+        Documentation/devicetree/bindings/spi/spi-bus.txt
+
+must be specified.
+
+Required properties:
+	- compatible:  	Must be one of the following, depending on the
+			model:
+			"maxim,max5481"
+			"maxim,max5482"
+			"maxim,max5483"
+			"maxim,max5484"
+
+Example:
+max548x: max548x@0 {
+	compatible = "maxim,max5482";
+	spi-max-frequency = <7000000>;
+	reg = <0>; /* chip-select */
+};

drivers/iio/potentiometer/Kconfig

···
 	  To compile this driver as a module, choose M here: the
 	  module will be called ds1803.
 
+config MAX5481
+        tristate "Maxim MAX5481-MAX5484 Digital Potentiometer driver"
+        depends on SPI
+        help
+          Say yes here to build support for the Maxim
+          MAX5481, MAX5482, MAX5483, MAX5484 digital potentiometer
+          chips.
+
+          To compile this driver as a module, choose M here: the
+          module will be called max5481.
+
 config MAX5487
         tristate "Maxim MAX5487/MAX5488/MAX5489 Digital Potentiometer driver"
         depends on SPI

drivers/iio/potentiometer/Makefile

···
 
 # When adding new entries keep the list in alphabetical order
 obj-$(CONFIG_DS1803) += ds1803.o
+obj-$(CONFIG_MAX5481) += max5481.o
 obj-$(CONFIG_MAX5487) += max5487.o
 obj-$(CONFIG_MCP4131) += mcp4131.o
 obj-$(CONFIG_MCP4531) += mcp4531.o

drivers/iio/potentiometer/max5481.c

···
+/*
+ * Maxim Integrated MAX5481-MAX5484 digital potentiometer driver
+ * Copyright 2016 Rockwell Collins
+ *
+ * Datasheet:
+ * http://datasheets.maximintegrated.com/en/ds/MAX5481-MAX5484.pdf
+ *
+ * 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/acpi.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/spi/spi.h>
+
+/* write wiper reg */
+#define MAX5481_WRITE_WIPER (0 << 4)
+/* copy wiper reg to NV reg */
+#define MAX5481_COPY_AB_TO_NV (2 << 4)
+/* copy NV reg to wiper reg */
+#define MAX5481_COPY_NV_TO_AB (3 << 4)
+
+#define MAX5481_MAX_POS    1023
+
+enum max5481_variant {
+	max5481,
+	max5482,
+	max5483,
+	max5484,
+};
+
+struct max5481_cfg {
+	int kohms;
+};
+
+static const struct max5481_cfg max5481_cfg[] = {
+	[max5481] = { .kohms =  10, },
+	[max5482] = { .kohms =  50, },
+	[max5483] = { .kohms =  10, },
+	[max5484] = { .kohms =  50, },
+};
+
+struct max5481_data {
+	struct spi_device *spi;
+	const struct max5481_cfg *cfg;
+	u8 msg[3] ____cacheline_aligned;
+};
+
+#define MAX5481_CHANNEL {					\
+	.type = IIO_RESISTANCE,					\
+	.indexed = 1,						\
+	.output = 1,						\
+	.channel = 0,						\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
+}
+
+static const struct iio_chan_spec max5481_channels[] = {
+	MAX5481_CHANNEL,
+};
+
+static int max5481_write_cmd(struct max5481_data *data, u8 cmd, u16 val)
+{
+	struct spi_device *spi = data->spi;
+
+	data->msg[0] = cmd;
+
+	switch (cmd) {
+	case MAX5481_WRITE_WIPER:
+		data->msg[1] = val >> 2;
+		data->msg[2] = (val & 0x3) << 6;
+		return spi_write(spi, data->msg, 3);
+
+	case MAX5481_COPY_AB_TO_NV:
+	case MAX5481_COPY_NV_TO_AB:
+		return spi_write(spi, data->msg, 1);
+
+	default:
+		return -EIO;
+	}
+}
+
+static int max5481_read_raw(struct iio_dev *indio_dev,
+		struct iio_chan_spec const *chan,
+		int *val, int *val2, long mask)
+{
+	struct max5481_data *data = iio_priv(indio_dev);
+
+	if (mask != IIO_CHAN_INFO_SCALE)
+		return -EINVAL;
+
+	*val = 1000 * data->cfg->kohms;
+	*val2 = MAX5481_MAX_POS;
+
+	return IIO_VAL_FRACTIONAL;
+}
+
+static int max5481_write_raw(struct iio_dev *indio_dev,
+		struct iio_chan_spec const *chan,
+		int val, int val2, long mask)
+{
+	struct max5481_data *data = iio_priv(indio_dev);
+
+	if (mask != IIO_CHAN_INFO_RAW)
+		return -EINVAL;
+
+	if (val < 0 || val > MAX5481_MAX_POS)
+		return -EINVAL;
+
+	return max5481_write_cmd(data, MAX5481_WRITE_WIPER, val);
+}
+
+static const struct iio_info max5481_info = {
+	.read_raw = max5481_read_raw,
+	.write_raw = max5481_write_raw,
+	.driver_module = THIS_MODULE,
+};
+
+#if defined(CONFIG_OF)
+static const struct of_device_id max5481_match[] = {
+	{ .compatible = "maxim,max5481", .data = &max5481_cfg[max5481] },
+	{ .compatible = "maxim,max5482", .data = &max5481_cfg[max5482] },
+	{ .compatible = "maxim,max5483", .data = &max5481_cfg[max5483] },
+	{ .compatible = "maxim,max5484", .data = &max5481_cfg[max5484] },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max5481_match);
+#endif
+
+static int max5481_probe(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev;
+	struct max5481_data *data;
+	const struct spi_device_id *id = spi_get_device_id(spi);
+	const struct of_device_id *match;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*data));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	dev_set_drvdata(&spi->dev, indio_dev);
+	data = iio_priv(indio_dev);
+
+	data->spi = spi;
+
+	match = of_match_device(of_match_ptr(max5481_match), &spi->dev);
+	if (match)
+		data->cfg = of_device_get_match_data(&spi->dev);
+	else
+		data->cfg = &max5481_cfg[id->driver_data];
+
+	indio_dev->name = id->name;
+	indio_dev->dev.parent = &spi->dev;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+
+	/* variant specific configuration */
+	indio_dev->info = &max5481_info;
+	indio_dev->channels = max5481_channels;
+	indio_dev->num_channels = ARRAY_SIZE(max5481_channels);
+
+	/* restore wiper from NV */
+	ret = max5481_write_cmd(data, MAX5481_COPY_NV_TO_AB, 0);
+	if (ret < 0)
+		return ret;
+
+	return iio_device_register(indio_dev);
+}
+
+static int max5481_remove(struct spi_device *spi)
+{
+	struct iio_dev *indio_dev = dev_get_drvdata(&spi->dev);
+	struct max5481_data *data = iio_priv(indio_dev);
+
+	iio_device_unregister(indio_dev);
+
+	/* save wiper reg to NV reg */
+	return max5481_write_cmd(data, MAX5481_COPY_AB_TO_NV, 0);
+}
+
+static const struct spi_device_id max5481_id_table[] = {
+	{ "max5481", max5481 },
+	{ "max5482", max5482 },
+	{ "max5483", max5483 },
+	{ "max5484", max5484 },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, max5481_id_table);
+
+#if defined(CONFIG_ACPI)
+static const struct acpi_device_id max5481_acpi_match[] = {
+	{ "max5481", max5481 },
+	{ "max5482", max5482 },
+	{ "max5483", max5483 },
+	{ "max5484", max5484 },
+	{ }
+};
+MODULE_DEVICE_TABLE(acpi, max5481_acpi_match);
+#endif
+
+static struct spi_driver max5481_driver = {
+	.driver = {
+		.name  = "max5481",
+		.owner = THIS_MODULE,
+		.of_match_table = of_match_ptr(max5481_match),
+		.acpi_match_table = ACPI_PTR(max5481_acpi_match),
+	},
+	.probe = max5481_probe,
+	.remove = max5481_remove,
+	.id_table = max5481_id_table,
+};
+
+module_spi_driver(max5481_driver);
+
+MODULE_AUTHOR("Maury Anderson <[e-mail]>");
+MODULE_DESCRIPTION("max5481 SPI driver");
+MODULE_LICENSE("GPL v2");