Re: [PATCH 2/2] iio: ad5272: Add support for Analog Devices digital potentiometers

On Wed, 10 Jan 2018 14:17:31 +0800
Phil Reid [off-list ref] wrote:

Add implementation for Analog Devices AD5272 and AD5274 digital
potentiometer devices.

Signed-off-by: Phil Reid <preid-qgqNFa1JUf/o2iN0hyhwsIdd74u8MsAO@public.gmane.org>

Hi Phil,

A few minor comments inline, but looking pretty good.

Jonathan

Could go all SPDX with the gpl part of this.  Personally I don't mind
much but we'll probably end up converting it over soon anyway.

+ */
+
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/iio/iio.h>
+#include <linux/module.h>
+
+#define  AD5272_RDAC_WR  1
+#define  AD5272_RDAC_RD  2
+#define  AD5272_CTL      7
+
+#define  AD5272_RDAC_WR_EN  BIT(1)
+
+struct ad5272_cfg {
+	int max_pos;
+	int kohms;
+	int shift;
+};
+
+enum ad5272_type {
+	AD5272_020,
+	AD5272_050,
+	AD5272_100,
+	AD5274_020,
+	AD5274_100,
+};
+
+static const struct ad5272_cfg ad5272_cfg[] = {
+	/* on-semiconductor parts */
+	[AD5272_020] = { .max_pos = 1024, .kohms = 20 },
+	[AD5272_050] = { .max_pos = 1024, .kohms = 50 },
+	[AD5272_100] = { .max_pos = 1024, .kohms = 100 },
+	[AD5274_020] = { .max_pos = 256,  .kohms = 20,  .shift = 2 },
+	[AD5274_100] = { .max_pos = 256,  .kohms = 100, .shift = 2 },
+};
+
+struct ad5272_data {
+	struct i2c_client       *client;
+	struct mutex            lock;
+	const struct ad5272_cfg *cfg;
+};
+
+static const struct iio_chan_spec ad5272_channel = {
+	.type = IIO_RESISTANCE,
+	.output = 1,
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
+};
+
+static int ad5272_write(struct ad5272_data *data, int reg, int val)
+{
+	u8 buf[2];
+	int ret;
+
+	buf[0] = ((reg & 0xf) << 2) | ((val >> 8) & 0x3);
+	buf[1] = (u8)val;

again, could do as buf[2]  = {...};

+
+	mutex_lock(&data->lock);
+	ret = i2c_master_send(data->client, buf, 2);

sizeof(buf) preferred.

+	mutex_unlock(&data->lock);
+	return ret < 0 ? ret : 0;
+}
+
+static int ad5272_read(struct ad5272_data *data, int reg, int *val)
+{
+	u8 buf[2];

Could assign value here for compactness.
	u8 buf[2] = {(reg & 0xf) << 2, 0);

It's a little paranoid to mask reg given you are controlling it entirely
in the driver and anything of more than 4 bits is a bug anyway.

+	int ret;
+
+	buf[0] = (reg & 0xf) << 2;
+	buf[1] = 0;
+
+	mutex_lock(&data->lock);
+	ret = i2c_master_send(data->client, buf, 2);
+	if (ret < 0)
+		goto error;
+
+	ret = i2c_master_recv(data->client, buf, 2);
+	if (ret < 0)
+		goto error;
+
+	*val = ((buf[0] & 0x3) << 8) | buf[1];
+	ret = 0;
+error:
+	mutex_unlock(&data->lock);
+	return ret;
+}
+
+static int ad5272_read_raw(struct iio_dev *indio_dev,
+			   struct iio_chan_spec const *chan,
+			   int *val, int *val2, long mask)
+{
+	struct ad5272_data *data = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW: {
+		ret = ad5272_read(data, AD5272_RDAC_RD, val);
+		*val = *val >> data->cfg->shift;
+		return ret ? ret : IIO_VAL_INT;
+	}
+	case IIO_CHAN_INFO_SCALE:
+		*val = 1000 * data->cfg->kohms;
+		*val2 = data->cfg->max_pos;
+		return IIO_VAL_FRACTIONAL;
+	}
+
+	return -EINVAL;
+}
+
+static int ad5272_write_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int val, int val2, long mask)
+{
+	struct ad5272_data *data = iio_priv(indio_dev);
+
+	if (mask != IIO_CHAN_INFO_RAW)
+		return -EINVAL;
+
+	if (val >= data->cfg->max_pos || val < 0)
+		return -EINVAL;

Also verify that val2 = 0 as otherwise the classic
1.999999 evaluates to 1 rather surprises users.

+
+	val = val << data->cfg->shift;

I would role this into the next line.

	return ad5272_write(data, AD5272_RDAC_WR, val << data->cfg->shift);

+
+	return ad5272_write(data, AD5272_RDAC_WR, val);
+}
+
+static const struct iio_info ad5272_info = {
+	.read_raw = ad5272_read_raw,
+	.write_raw = ad5272_write_raw,
+	.driver_module = THIS_MODULE,

.driver_module no longer exists so just drop this.
We do the equivalent with some macro tricks to avoid having
to have this same line in every driver.

+};
+
+static int ad5272_probe(struct i2c_client *client,
+			const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct gpio_desc *reset_gpio;
+	struct iio_dev *indio_dev;
+	struct ad5272_data *data;
+	int ret;
+
+	reset_gpio = devm_gpiod_get_optional(&client->dev, "reset",
+		GPIOD_OUT_LOW);
+	if (IS_ERR(reset_gpio))
+		return PTR_ERR(reset_gpio);
+
+	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;
+	mutex_init(&data->lock);
+	data->cfg = &ad5272_cfg[id->driver_data];

Calling it cfg kind of implies config to me whereas this is
chip type specific data.

+
+	ret = ad5272_write(data, AD5272_CTL, AD5272_RDAC_WR_EN);
+	if (ret < 0)
+		return -ENODEV;
+
+	indio_dev->dev.parent = dev;
+	indio_dev->info = &ad5272_info;
+	indio_dev->channels = &ad5272_channel;
+	indio_dev->num_channels = 1;
+	indio_dev->name = client->name;
+
+	return devm_iio_device_register(dev, indio_dev);
+}
+
+#if defined(CONFIG_OF)
+static const struct of_device_id ad5272_dt_ids[] = {
+	{ .compatible = "adi,ad5272-020", .data = &ad5272_cfg[AD5272_020] },

Why do this rather than stash the index in the data parameter and look up later
(more consistent with the i2c_device_id table below)?

+	{ .compatible = "adi,ad5272-050", .data = &ad5272_cfg[AD5272_050] },
+	{ .compatible = "adi,ad5272-100", .data = &ad5272_cfg[AD5272_100] },
+	{ .compatible = "adi,ad5274-020", .data = &ad5272_cfg[AD5274_020] },
+	{ .compatible = "adi,ad5274-100", .data = &ad5272_cfg[AD5274_100] },
+	{}
+};
+MODULE_DEVICE_TABLE(of, ad5272_dt_ids);
+#endif /* CONFIG_OF */
+
+static const struct i2c_device_id ad5272_id[] = {
+	{ "ad5272-020", AD5272_020 },
+	{ "ad5272-050", AD5272_050 },
+	{ "ad5272-100", AD5272_100 },
+	{ "ad5274-020", AD5274_020 },
+	{ "ad5274-100", AD5274_100 },
+	{}
+};
+MODULE_DEVICE_TABLE(i2c, ad5272_id);
+
+static struct i2c_driver ad5272_driver = {
+	.driver = {
+		.name	= "ad5272",
+		.of_match_table = of_match_ptr(ad5272_dt_ids),
+	},
+	.probe		= ad5272_probe,
+	.id_table	= ad5272_id,
+};
+
+module_i2c_driver(ad5272_driver);
+
+MODULE_AUTHOR("Phil Reid [off-list ref]");
+MODULE_DESCRIPTION("AD5272 digital potentiometer");
+MODULE_LICENSE("GPL v2");