iio: amplifiers: hmc425a: Add support for HMC425A attenuator

This patch adds support for the HMC425A 0.5 dB LSB GaAs MMIC 6-BIT
DIGITAL POSITIVE CONTROL ATTENUATOR, 2.2 - 8.0 GHz.

Datasheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/hmc425A.pdf

Signed-off-by: Michael Hennerich <[e-mail]>
Signed-off-by: Alexandru Ardelean <[e-mail]>
Signed-off-by: Beniamin Bia <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/amplifiers/Kconfig

···
 	  To compile this driver as a module, choose M here: the
 	  module will be called ad8366.
 
+config HMC425
+	tristate "Analog Devices HMC425A and similar GPIO Gain Amplifiers"
+	depends on GPIOLIB
+	help
+	  Say yes here to build support for Analog Devices HMC425A and similar
+	  gain amplifiers or step attenuators.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called hmc425a.
+
 endmenu

drivers/iio/amplifiers/Makefile

···
 
 # When adding new entries keep the list in alphabetical order
 obj-$(CONFIG_AD8366) += ad8366.o
+obj-$(CONFIG_HMC425) += hmc425a.o

drivers/iio/amplifiers/hmc425a.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * HMC425A and similar Gain Amplifiers
+ *
+ * Copyright 2020 Analog Devices Inc.
+ */
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/regulator/consumer.h>
+#include <linux/sysfs.h>
+
+enum hmc425a_type {
+	ID_HMC425A,
+};
+
+struct hmc425a_chip_info {
+	const char			*name;
+	const struct iio_chan_spec	*channels;
+	unsigned int			num_channels;
+	unsigned int			num_gpios;
+	int				gain_min;
+	int				gain_max;
+	int				default_gain;
+};
+
+struct hmc425a_state {
+	struct	regulator *reg;
+	struct	mutex lock; /* protect sensor state */
+	struct	hmc425a_chip_info *chip_info;
+	struct	gpio_descs *gpios;
+	enum	hmc425a_type type;
+	u32	gain;
+};
+
+static int hmc425a_write(struct iio_dev *indio_dev, u32 value)
+{
+	struct hmc425a_state *st = iio_priv(indio_dev);
+	DECLARE_BITMAP(values, BITS_PER_TYPE(value));
+
+	values[0] = value;
+
+	gpiod_set_array_value_cansleep(st->gpios->ndescs, st->gpios->desc,
+				       NULL, values);
+	return 0;
+}
+
+static int hmc425a_read_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan, int *val,
+			    int *val2, long m)
+{
+	struct hmc425a_state *st = iio_priv(indio_dev);
+	int code, gain = 0;
+	int ret;
+
+	mutex_lock(&st->lock);
+	switch (m) {
+	case IIO_CHAN_INFO_HARDWAREGAIN:
+		code = st->gain;
+
+		switch (st->type) {
+		case ID_HMC425A:
+			gain = ~code * -500;
+			break;
+		}
+
+		*val = gain / 1000;
+		*val2 = (gain % 1000) * 1000;
+
+		ret = IIO_VAL_INT_PLUS_MICRO_DB;
+		break;
+	default:
+		ret = -EINVAL;
+	}
+	mutex_unlock(&st->lock);
+
+	return ret;
+};
+
+static int hmc425a_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan, int val,
+			     int val2, long mask)
+{
+	struct hmc425a_state *st = iio_priv(indio_dev);
+	struct hmc425a_chip_info *inf = st->chip_info;
+	int code = 0, gain;
+	int ret;
+
+	if (val < 0)
+		gain = (val * 1000) - (val2 / 1000);
+	else
+		gain = (val * 1000) + (val2 / 1000);
+
+	if (gain > inf->gain_max || gain < inf->gain_min)
+		return -EINVAL;
+
+	switch (st->type) {
+	case ID_HMC425A:
+		code = ~((abs(gain) / 500) & 0x3F);
+		break;
+	}
+
+	mutex_lock(&st->lock);
+	switch (mask) {
+	case IIO_CHAN_INFO_HARDWAREGAIN:
+		st->gain = code;
+
+		ret = hmc425a_write(indio_dev, st->gain);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+	mutex_unlock(&st->lock);
+
+	return ret;
+}
+
+static int hmc425a_write_raw_get_fmt(struct iio_dev *indio_dev,
+				     struct iio_chan_spec const *chan,
+				     long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_HARDWAREGAIN:
+		return IIO_VAL_INT_PLUS_MICRO_DB;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info hmc425a_info = {
+	.read_raw = &hmc425a_read_raw,
+	.write_raw = &hmc425a_write_raw,
+	.write_raw_get_fmt = &hmc425a_write_raw_get_fmt,
+};
+
+#define HMC425A_CHAN(_channel)						\
+{									\
+	.type = IIO_VOLTAGE,						\
+	.output = 1,							\
+	.indexed = 1,							\
+	.channel = _channel,						\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_HARDWAREGAIN),		\
+}
+
+static const struct iio_chan_spec hmc425a_channels[] = {
+	HMC425A_CHAN(0),
+};
+
+/* Match table for of_platform binding */
+static const struct of_device_id hmc425a_of_match[] = {
+	{ .compatible = "adi,hmc425a", .data = (void *)ID_HMC425A },
+	{},
+};
+MODULE_DEVICE_TABLE(of, hmc425a_of_match);
+
+static void hmc425a_reg_disable(void *data)
+{
+	struct hmc425a_state *st = data;
+
+	regulator_disable(st->reg);
+}
+
+static struct hmc425a_chip_info hmc425a_chip_info_tbl[] = {
+	[ID_HMC425A] = {
+		.name = "hmc425a",
+		.channels = hmc425a_channels,
+		.num_channels = ARRAY_SIZE(hmc425a_channels),
+		.num_gpios = 6,
+		.gain_min = -31500,
+		.gain_max = 0,
+		.default_gain = -0x40, /* set default gain -31.5db*/
+	},
+};
+
+static int hmc425a_probe(struct platform_device *pdev)
+{
+	struct iio_dev *indio_dev;
+	struct hmc425a_state *st;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	st = iio_priv(indio_dev);
+	st->type = (enum hmc425a_type)of_device_get_match_data(&pdev->dev);
+
+	st->chip_info = &hmc425a_chip_info_tbl[st->type];
+	indio_dev->num_channels = st->chip_info->num_channels;
+	indio_dev->channels = st->chip_info->channels;
+	indio_dev->name = st->chip_info->name;
+	st->gain = st->chip_info->default_gain;
+
+	st->gpios = devm_gpiod_get_array(&pdev->dev, "ctrl", GPIOD_OUT_LOW);
+	if (IS_ERR(st->gpios)) {
+		ret = PTR_ERR(st->gpios);
+		if (ret != -EPROBE_DEFER)
+			dev_err(&pdev->dev, "failed to get gpios\n");
+		return ret;
+	}
+
+	if (st->gpios->ndescs != st->chip_info->num_gpios) {
+		dev_err(&pdev->dev, "%d GPIOs needed to operate\n",
+			st->chip_info->num_gpios);
+		return -ENODEV;
+	}
+
+	st->reg = devm_regulator_get(&pdev->dev, "vcc-supply");
+	if (IS_ERR(st->reg))
+		return PTR_ERR(st->reg);
+
+	ret = regulator_enable(st->reg);
+	if (ret)
+		return ret;
+	ret = devm_add_action_or_reset(&pdev->dev, hmc425a_reg_disable, st);
+	if (ret)
+		return ret;
+
+	mutex_init(&st->lock);
+
+	indio_dev->dev.parent = &pdev->dev;
+	indio_dev->info = &hmc425a_info;
+	indio_dev->modes = INDIO_DIRECT_MODE;
+
+	return devm_iio_device_register(&pdev->dev, indio_dev);
+}
+
+static struct platform_driver hmc425a_driver = {
+	.driver = {
+		.name = KBUILD_MODNAME,
+		.of_match_table = hmc425a_of_match,
+	},
+	.probe = hmc425a_probe,
+};
+module_platform_driver(hmc425a_driver);
+
+MODULE_AUTHOR("Michael Hennerich <[e-mail]>");
+MODULE_DESCRIPTION("Analog Devices HMC425A and similar GPIO control Gain Amplifiers");
+MODULE_LICENSE("GPL v2");