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

[Jonathan Cameron <jic23-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Wed, 10 Jan 2018 14:17:31 +0800
Phil Reid <preid-qgqNFa1JUf/o2iN0hyhwsIdd74u8MsAO@public.gmane.org> 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

> ---
>  drivers/iio/potentiometer/Kconfig  |  10 ++
>  drivers/iio/potentiometer/Makefile |   1 +
>  drivers/iio/potentiometer/ad5272.c | 219 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 230 insertions(+)
>  create mode 100644 drivers/iio/potentiometer/ad5272.c
> 
> diff --git a/drivers/iio/potentiometer/Kconfig b/drivers/iio/potentiometer/Kconfig
> index 8bf2825..0b04063 100644
> --- a/drivers/iio/potentiometer/Kconfig
> +++ b/drivers/iio/potentiometer/Kconfig
> @@ -5,6 +5,16 @@
>  
>  menu "Digital potentiometers"
>  
> +config AD5272
> +	tristate "Analog Devices AD5272 Digital Potentiometer driver"
> +	depends on I2C
> +	help
> +	  Say yes here to build support for the Analog Devices AD5272
> +	  digital potentiometer chip.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called ad5272.
> +
>  config DS1803
>  	tristate "Maxim Integrated DS1803 Digital Potentiometer driver"
>  	depends on I2C
> diff --git a/drivers/iio/potentiometer/Makefile b/drivers/iio/potentiometer/Makefile
> index 2260d40..498bbb8 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-$(CONFIG_AD5272) += ad5272.o
>  obj-$(CONFIG_DS1803) += ds1803.o
>  obj-$(CONFIG_MAX5481) += max5481.o
>  obj-$(CONFIG_MAX5487) += max5487.o
> diff --git a/drivers/iio/potentiometer/ad5272.c b/drivers/iio/potentiometer/ad5272.c
> new file mode 100644
> index 0000000..b9208c2
> --- /dev/null
> +++ b/drivers/iio/potentiometer/ad5272.c
> @@ -0,0 +1,219 @@
> +/*
> + * Analog Devices AD5372 digital potentiometer driver
> + * Copyright (C) 2018 Phil Reid <preid-qgqNFa1JUf/o2iN0hyhwsIdd74u8MsAO@public.gmane.org>
> + *
> + * Datasheet: http://www.analog.com/media/en/technical-documentation/data-sheets/AD5272_5274.pdf
> + *
> + * DEVID	#Wipers	#Positions	Resistor Opts (kOhm)	i2c address
> + * ad5272	1	1024		20, 50, 100		01011xx
> + * ad5274	1	256		20, 100			01011xx
> + *
> + * 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.

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 <preid-TeWIRZsGUAnP+dxuUfoltA@public.gmane.org>");
> +MODULE_DESCRIPTION("AD5272 digital potentiometer");
> +MODULE_LICENSE("GPL v2");