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Date:   Sun, 25 Apr 2021 16:46:13 +0100
From:   Jonathan Cameron <jic23@kernel.org>
To:     Tomasz Duszynski <tomasz.duszynski@octakon.com>
Cc:     <linux-iio@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <devicetree@vger.kernel.org>, <lars@metafoo.de>,
        <robh+dt@kernel.org>
Subject: Re: [PATCH 1/3] iio: sps30: separate core and interface specific
 code
Message-ID: <20210425164613.7eda8f6c@jic23-huawei>
In-Reply-To: <20210425135546.57343-2-tomasz.duszynski@octakon.com>
References: <20210425135546.57343-1-tomasz.duszynski@octakon.com>
        <20210425135546.57343-2-tomasz.duszynski@octakon.com>
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On Sun, 25 Apr 2021 15:55:44 +0200
Tomasz Duszynski <tomasz.duszynski@octakon.com> wrote:

> Move code responsible for handling i2c communication to a separate file.
> Rationale for this change is preparation for adding support for serial
> communication.
> 
> Signed-off-by: Tomasz Duszynski <tomasz.duszynski@octakon.com>

Hi Tomasz,

This seems rather less minimal than I'd usually expect for this sort of refactor
but (other than a few things commented on inline) it seems like all the other
bits of refactoring are sensible to me.

Thanks,

Jonathan

> ---
>  MAINTAINERS                      |   1 +
>  drivers/iio/chemical/Kconfig     |  13 +-
>  drivers/iio/chemical/Makefile    |   1 +
>  drivers/iio/chemical/sps30.c     | 270 ++++++-------------------------
>  drivers/iio/chemical/sps30.h     |  73 +++++++++
>  drivers/iio/chemical/sps30_i2c.c | 256 +++++++++++++++++++++++++++++
>  6 files changed, 391 insertions(+), 223 deletions(-)
>  create mode 100644 drivers/iio/chemical/sps30.h
>  create mode 100644 drivers/iio/chemical/sps30_i2c.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index ccc59fd7e5c0..4b39a9c48736 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -16137,6 +16137,7 @@ M:	Tomasz Duszynski <tduszyns@gmail.com>
>  S:	Maintained
>  F:	Documentation/devicetree/bindings/iio/chemical/sensirion,sps30.yaml
>  F:	drivers/iio/chemical/sps30.c
> +F:	drivers/iio/chemical/sps30_i2c.c
>  
>  SERIAL DEVICE BUS
>  M:	Rob Herring <robh@kernel.org>
> diff --git a/drivers/iio/chemical/Kconfig b/drivers/iio/chemical/Kconfig
> index 10bb431bc3ce..82af5f62fbc6 100644
> --- a/drivers/iio/chemical/Kconfig
> +++ b/drivers/iio/chemical/Kconfig
> @@ -133,8 +133,6 @@ config SENSIRION_SGP30
>  
>  config SPS30
>  	tristate "SPS30 particulate matter sensor"

One option here is to simplify the Kconfig memu options by
dropping the text above so the option is hidden then selecting
this option (rather than depends) for the bus specific drivers.

> -	depends on I2C
> -	select CRC8
>  	select IIO_BUFFER
>  	select IIO_TRIGGERED_BUFFER
>  	help
> @@ -144,6 +142,17 @@ config SPS30
>  	  To compile this driver as a module, choose M here: the module will
>  	  be called sps30.
>  
> +config SPS30_I2C
> +	tristate "SPS30 particulate matter sensor I2C driver"
> +	depends on SPS30 && I2C
> +	select CRC8
> +	help
> +	  Say Y here to build support for the Sensirion SPS30 I2C interface
> +	  driver.
> +
> +	  To compile this driver as a module, choose M here: the module will
> +	  be called sps30_i2c.
> +
>  config VZ89X
>  	tristate "SGX Sensortech MiCS VZ89X VOC sensor"
>  	depends on I2C
> diff --git a/drivers/iio/chemical/Makefile b/drivers/iio/chemical/Makefile
> index fef63dd5bf92..41c264a229c0 100644
> --- a/drivers/iio/chemical/Makefile
> +++ b/drivers/iio/chemical/Makefile
> @@ -17,4 +17,5 @@ obj-$(CONFIG_SCD30_I2C) += scd30_i2c.o
>  obj-$(CONFIG_SCD30_SERIAL) += scd30_serial.o
>  obj-$(CONFIG_SENSIRION_SGP30)	+= sgp30.o
>  obj-$(CONFIG_SPS30) += sps30.o
> +obj-$(CONFIG_SPS30_I2C) += sps30_i2c.o
>  obj-$(CONFIG_VZ89X)		+= vz89x.o
> diff --git a/drivers/iio/chemical/sps30.c b/drivers/iio/chemical/sps30.c
> index 7486591588c3..ec9db99e324c 100644
> --- a/drivers/iio/chemical/sps30.c
> +++ b/drivers/iio/chemical/sps30.c
> @@ -3,11 +3,8 @@
>   * Sensirion SPS30 particulate matter sensor driver
>   *
>   * Copyright (c) Tomasz Duszynski <tduszyns@gmail.com>
> - *
> - * I2C slave address: 0x69
>   */
>  
> -#include <asm/unaligned.h>
>  #include <linux/crc8.h>
>  #include <linux/delay.h>
>  #include <linux/i2c.h>
> @@ -19,27 +16,14 @@
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  
> -#define SPS30_CRC8_POLYNOMIAL 0x31
> -/* max number of bytes needed to store PM measurements or serial string */
> -#define SPS30_MAX_READ_SIZE 48
> +#include "sps30.h"
> +
>  /* sensor measures reliably up to 3000 ug / m3 */
>  #define SPS30_MAX_PM 3000
>  /* minimum and maximum self cleaning periods in seconds */
>  #define SPS30_AUTO_CLEANING_PERIOD_MIN 0
>  #define SPS30_AUTO_CLEANING_PERIOD_MAX 604800
>  
> -/* SPS30 commands */
> -#define SPS30_START_MEAS 0x0010
> -#define SPS30_STOP_MEAS 0x0104
> -#define SPS30_RESET 0xd304
> -#define SPS30_READ_DATA_READY_FLAG 0x0202
> -#define SPS30_READ_DATA 0x0300
> -#define SPS30_READ_SERIAL 0xd033
> -#define SPS30_START_FAN_CLEANING 0x5607
> -#define SPS30_AUTO_CLEANING_PERIOD 0x8004
> -/* not a sensor command per se, used only to distinguish write from read */
> -#define SPS30_READ_AUTO_CLEANING_PERIOD 0x8005
> -
>  enum {
>  	PM1,
>  	PM2P5,
> @@ -52,114 +36,9 @@ enum {
>  	MEASURING,
>  };
>  
> -struct sps30_state {
> -	struct i2c_client *client;
> -	/*
> -	 * Guards against concurrent access to sensor registers.
> -	 * Must be held whenever sequence of commands is to be executed.
> -	 */
> -	struct mutex lock;
> -	int state;
> -};
> -
> -DECLARE_CRC8_TABLE(sps30_crc8_table);
> -
> -static int sps30_write_then_read(struct sps30_state *state, u8 *txbuf,
> -				 int txsize, u8 *rxbuf, int rxsize)
> -{
> -	int ret;
> -
> -	/*
> -	 * Sensor does not support repeated start so instead of
> -	 * sending two i2c messages in a row we just send one by one.
> -	 */
> -	ret = i2c_master_send(state->client, txbuf, txsize);
> -	if (ret != txsize)
> -		return ret < 0 ? ret : -EIO;
> -
> -	if (!rxbuf)
> -		return 0;
> -
> -	ret = i2c_master_recv(state->client, rxbuf, rxsize);
> -	if (ret != rxsize)
> -		return ret < 0 ? ret : -EIO;
> -
> -	return 0;
> -}
> -
> -static int sps30_do_cmd(struct sps30_state *state, u16 cmd, u8 *data, int size)
> -{
> -	/*
> -	 * Internally sensor stores measurements in a following manner:
> -	 *
> -	 * PM1: upper two bytes, crc8, lower two bytes, crc8
> -	 * PM2P5: upper two bytes, crc8, lower two bytes, crc8
> -	 * PM4: upper two bytes, crc8, lower two bytes, crc8
> -	 * PM10: upper two bytes, crc8, lower two bytes, crc8
> -	 *
> -	 * What follows next are number concentration measurements and
> -	 * typical particle size measurement which we omit.
> -	 */
> -	u8 buf[SPS30_MAX_READ_SIZE] = { cmd >> 8, cmd };
> -	int i, ret = 0;
> -
> -	switch (cmd) {
> -	case SPS30_START_MEAS:
> -		buf[2] = 0x03;
> -		buf[3] = 0x00;
> -		buf[4] = crc8(sps30_crc8_table, &buf[2], 2, CRC8_INIT_VALUE);
> -		ret = sps30_write_then_read(state, buf, 5, NULL, 0);
> -		break;
> -	case SPS30_STOP_MEAS:
> -	case SPS30_RESET:
> -	case SPS30_START_FAN_CLEANING:
> -		ret = sps30_write_then_read(state, buf, 2, NULL, 0);
> -		break;
> -	case SPS30_READ_AUTO_CLEANING_PERIOD:
> -		buf[0] = SPS30_AUTO_CLEANING_PERIOD >> 8;
> -		buf[1] = (u8)(SPS30_AUTO_CLEANING_PERIOD & 0xff);
> -		fallthrough;
> -	case SPS30_READ_DATA_READY_FLAG:
> -	case SPS30_READ_DATA:
> -	case SPS30_READ_SERIAL:
> -		/* every two data bytes are checksummed */
> -		size += size / 2;
> -		ret = sps30_write_then_read(state, buf, 2, buf, size);
> -		break;
> -	case SPS30_AUTO_CLEANING_PERIOD:
> -		buf[2] = data[0];
> -		buf[3] = data[1];
> -		buf[4] = crc8(sps30_crc8_table, &buf[2], 2, CRC8_INIT_VALUE);
> -		buf[5] = data[2];
> -		buf[6] = data[3];
> -		buf[7] = crc8(sps30_crc8_table, &buf[5], 2, CRC8_INIT_VALUE);
> -		ret = sps30_write_then_read(state, buf, 8, NULL, 0);
> -		break;
> -	}
> -
> -	if (ret)
> -		return ret;
> -
> -	/* validate received data and strip off crc bytes */
> -	for (i = 0; i < size; i += 3) {
> -		u8 crc = crc8(sps30_crc8_table, &buf[i], 2, CRC8_INIT_VALUE);
> -
> -		if (crc != buf[i + 2]) {
> -			dev_err(&state->client->dev,
> -				"data integrity check failed\n");
> -			return -EIO;
> -		}
> -
> -		*data++ = buf[i];
> -		*data++ = buf[i + 1];
> -	}
> -
> -	return 0;
> -}
> -
> -static s32 sps30_float_to_int_clamped(const u8 *fp)
> +static s32 sps30_float_to_int_clamped(__be32 fp)
>  {
> -	int val = get_unaligned_be32(fp);
> +	int val = be32_to_cpu(fp);
>  	int mantissa = val & GENMASK(22, 0);
>  	/* this is fine since passed float is always non-negative */
>  	int exp = val >> 23;
> @@ -188,38 +67,35 @@ static s32 sps30_float_to_int_clamped(const u8 *fp)
>  
>  static int sps30_do_meas(struct sps30_state *state, s32 *data, int size)
>  {
> -	int i, ret, tries = 5;
> -	u8 tmp[16];
> +	int i, ret;
>  
>  	if (state->state == RESET) {
> -		ret = sps30_do_cmd(state, SPS30_START_MEAS, NULL, 0);
> +		ret = sps30_start_meas(state);
>  		if (ret)
>  			return ret;
>  
>  		state->state = MEASURING;
>  	}
>  
> -	while (tries--) {
> -		ret = sps30_do_cmd(state, SPS30_READ_DATA_READY_FLAG, tmp, 2);
> -		if (ret)
> -			return -EIO;
> +	ret = sps30_read_meas(state, data, size);
> +	if (ret)
> +		return ret;
>  
> -		/* new measurements ready to be read */
> -		if (tmp[1] == 1)
> -			break;
> +	for (i = 0; i < size; i++)
> +		data[i] = sps30_float_to_int_clamped((__force __be32)data[i]);
>  
> -		msleep_interruptible(300);
> -	}
> +	return 0;
> +}
>  
> -	if (tries == -1)
> -		return -ETIMEDOUT;
> +static int sps30_do_reset(struct sps30_state *state)
> +{
> +	int ret;
>  
> -	ret = sps30_do_cmd(state, SPS30_READ_DATA, tmp, sizeof(int) * size);
> +	ret = sps30_reset(state);
>  	if (ret)
>  		return ret;
>  
> -	for (i = 0; i < size; i++)
> -		data[i] = sps30_float_to_int_clamped(&tmp[4 * i]);
> +	state->state = RESET;
>  
>  	return 0;
>  }
> @@ -310,24 +186,6 @@ static int sps30_read_raw(struct iio_dev *indio_dev,
>  	return -EINVAL;
>  }
>  
> -static int sps30_do_cmd_reset(struct sps30_state *state)
> -{
> -	int ret;
> -
> -	ret = sps30_do_cmd(state, SPS30_RESET, NULL, 0);
> -	msleep(300);
> -	/*
> -	 * Power-on-reset causes sensor to produce some glitch on i2c bus and
> -	 * some controllers end up in error state. Recover simply by placing
> -	 * some data on the bus, for example STOP_MEAS command, which
> -	 * is NOP in this case.
> -	 */
> -	sps30_do_cmd(state, SPS30_STOP_MEAS, NULL, 0);
> -	state->state = RESET;
> -
> -	return ret;
> -}
> -
>  static ssize_t start_cleaning_store(struct device *dev,
>  				    struct device_attribute *attr,
>  				    const char *buf, size_t len)
> @@ -340,7 +198,7 @@ static ssize_t start_cleaning_store(struct device *dev,
>  		return -EINVAL;
>  
>  	mutex_lock(&state->lock);
> -	ret = sps30_do_cmd(state, SPS30_START_FAN_CLEANING, NULL, 0);
> +	ret = sps30_clean_fan(state);
>  	mutex_unlock(&state->lock);
>  	if (ret)
>  		return ret;
> @@ -349,31 +207,28 @@ static ssize_t start_cleaning_store(struct device *dev,
>  }
>  
>  static ssize_t cleaning_period_show(struct device *dev,
> -				      struct device_attribute *attr,
> -				      char *buf)
> +				    struct device_attribute *attr,
> +				    char *buf)
>  {
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct sps30_state *state = iio_priv(indio_dev);
> -	u8 tmp[4];
> -	int ret;
> +	int val, ret;
>  
>  	mutex_lock(&state->lock);
> -	ret = sps30_do_cmd(state, SPS30_READ_AUTO_CLEANING_PERIOD, tmp, 4);
> +	ret = sps30_read_cleaning_period(state, &val);
>  	mutex_unlock(&state->lock);
>  	if (ret)
>  		return ret;
>  
> -	return sprintf(buf, "%d\n", get_unaligned_be32(tmp));
> +	return sprintf(buf, "%d\n", be32_to_cpu((__force __be32)val));

As below, I'm not seeing the necessity of this cast.  Just make val a
__be32 and deal with parameters being passed around as that type.

>  }
>  
> -static ssize_t cleaning_period_store(struct device *dev,
> -				       struct device_attribute *attr,
> -				       const char *buf, size_t len)
> +static ssize_t cleaning_period_store(struct device *dev, struct device_attribute *attr,
> +				     const char *buf, size_t len)
>  {
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct sps30_state *state = iio_priv(indio_dev);
>  	int val, ret;
> -	u8 tmp[4];
>  
>  	if (kstrtoint(buf, 0, &val))
>  		return -EINVAL;
> @@ -382,10 +237,8 @@ static ssize_t cleaning_period_store(struct device *dev,
>  	    (val > SPS30_AUTO_CLEANING_PERIOD_MAX))
>  		return -EINVAL;
>  
> -	put_unaligned_be32(val, tmp);
> -
>  	mutex_lock(&state->lock);
> -	ret = sps30_do_cmd(state, SPS30_AUTO_CLEANING_PERIOD, tmp, 0);
> +	ret = sps30_write_cleaning_period(state, (__force int)cpu_to_be32(val));

I guess this is related to the below question of the type of period parameter.
I'd make it a be32 directly if that's what it actually is!

>  	if (ret) {
>  		mutex_unlock(&state->lock);
>  		return ret;
> @@ -397,7 +250,7 @@ static ssize_t cleaning_period_store(struct device *dev,
>  	 * sensor requires reset in order to return up to date self cleaning
>  	 * period
>  	 */
> -	ret = sps30_do_cmd_reset(state);
> +	ret = sps30_do_reset(state);
>  	if (ret)
>  		dev_warn(dev,
>  			 "period changed but reads will return the old value\n");
> @@ -460,90 +313,65 @@ static const struct iio_chan_spec sps30_channels[] = {
>  	IIO_CHAN_SOFT_TIMESTAMP(4),
>  };
>  
> -static void sps30_stop_meas(void *data)
> +static void sps30_devm_stop_meas(void *data)
>  {
>  	struct sps30_state *state = data;
>  
> -	sps30_do_cmd(state, SPS30_STOP_MEAS, NULL, 0);
> +	if (state->state == MEASURING)
> +		sps30_stop_meas(state);
>  }
>  
>  static const unsigned long sps30_scan_masks[] = { 0x0f, 0x00 };
>  
> -static int sps30_probe(struct i2c_client *client)
> +int sps30_probe(struct device *dev, const char *name, void *priv, const struct sps30_ops *ops)
>  {
>  	struct iio_dev *indio_dev;
>  	struct sps30_state *state;
> -	u8 buf[32];
>  	int ret;
>  
> -	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> -		return -EOPNOTSUPP;
> -
> -	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*state));
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*state));
>  	if (!indio_dev)
>  		return -ENOMEM;
>  
> +	dev_set_drvdata(dev, indio_dev);
> +
>  	state = iio_priv(indio_dev);
> -	i2c_set_clientdata(client, indio_dev);
> -	state->client = client;
> -	state->state = RESET;
> +	state->dev = dev;
> +	state->priv = priv;
> +	state->ops = ops;
> +	mutex_init(&state->lock);
> +
>  	indio_dev->info = &sps30_info;
> -	indio_dev->name = client->name;
> +	indio_dev->name = name;
>  	indio_dev->channels = sps30_channels;
>  	indio_dev->num_channels = ARRAY_SIZE(sps30_channels);
>  	indio_dev->modes = INDIO_DIRECT_MODE;
>  	indio_dev->available_scan_masks = sps30_scan_masks;
>  
> -	mutex_init(&state->lock);
> -	crc8_populate_msb(sps30_crc8_table, SPS30_CRC8_POLYNOMIAL);
> -
> -	ret = sps30_do_cmd_reset(state);
> +	ret = sps30_do_reset(state);
>  	if (ret) {
> -		dev_err(&client->dev, "failed to reset device\n");
> +		dev_err(dev, "failed to reset device\n");
>  		return ret;
>  	}
>  
> -	ret = sps30_do_cmd(state, SPS30_READ_SERIAL, buf, sizeof(buf));
> +	ret = sps30_show_info(state);
>  	if (ret) {
> -		dev_err(&client->dev, "failed to read serial number\n");
> +		dev_err(dev, "failed to read device info\n");
>  		return ret;
>  	}
> -	/* returned serial number is already NUL terminated */
> -	dev_info(&client->dev, "serial number: %s\n", buf);
>  
> -	ret = devm_add_action_or_reset(&client->dev, sps30_stop_meas, state);
> +	ret = devm_add_action_or_reset(dev, sps30_devm_stop_meas, state);
>  	if (ret)
>  		return ret;
>  
> -	ret = devm_iio_triggered_buffer_setup(&client->dev, indio_dev, NULL,
> +	ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
>  					      sps30_trigger_handler, NULL);
>  	if (ret)
>  		return ret;
>  
> -	return devm_iio_device_register(&client->dev, indio_dev);
> +	return devm_iio_device_register(dev, indio_dev);
>  }
> -
> -static const struct i2c_device_id sps30_id[] = {
> -	{ "sps30" },
> -	{ }
> -};
> -MODULE_DEVICE_TABLE(i2c, sps30_id);
> -
> -static const struct of_device_id sps30_of_match[] = {
> -	{ .compatible = "sensirion,sps30" },
> -	{ }
> -};
> -MODULE_DEVICE_TABLE(of, sps30_of_match);
> -
> -static struct i2c_driver sps30_driver = {
> -	.driver = {
> -		.name = "sps30",
> -		.of_match_table = sps30_of_match,
> -	},
> -	.id_table = sps30_id,
> -	.probe_new = sps30_probe,
> -};
> -module_i2c_driver(sps30_driver);
> +EXPORT_SYMBOL(sps30_probe);
>  
>  MODULE_AUTHOR("Tomasz Duszynski <tduszyns@gmail.com>");
>  MODULE_DESCRIPTION("Sensirion SPS30 particulate matter sensor driver");
> diff --git a/drivers/iio/chemical/sps30.h b/drivers/iio/chemical/sps30.h
> new file mode 100644
> index 000000000000..d2b7140fdeb4
> --- /dev/null
> +++ b/drivers/iio/chemical/sps30.h
> @@ -0,0 +1,73 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _SPS30_H
> +#define _SPS30_H
> +
> +struct sps30_state;
> +struct sps30_ops {
> +	int (*start_meas)(struct sps30_state *state);
> +	int (*stop_meas)(struct sps30_state *state);
> +	int (*read_meas)(struct sps30_state *state, int *meas, int num);
> +	int (*reset)(struct sps30_state *state);
> +	int (*clean_fan)(struct sps30_state *state);
> +	int (*read_cleaning_period)(struct sps30_state *state, int *period);

As mentioned below, I think period should be a fixed width type.

> +	int (*write_cleaning_period)(struct sps30_state *state, int period);
> +	int (*show_info)(struct sps30_state *state);
> +};
> +
> +struct sps30_state {
> +	/* serialize access to the device */
> +	struct mutex lock;
> +	struct device *dev;
> +	int state;
> +	/*
> +	 * priv pointer is solely for serdev driver private data. We keep it
> +	 * here because driver_data inside dev has been already used for iio and
> +	 * struct serdev_device doesn't have one.
> +	 */
> +	void *priv;
> +	const struct sps30_ops *ops;
> +};
> +
> +int sps30_probe(struct device *dev, const char *name, void *priv, const struct sps30_ops *ops);
> +
> +static inline int sps30_start_meas(struct sps30_state *state)
> +{
> +	return state->ops->start_meas(state);

I'm not convinced the following wrappers are worthwhile.
Most of these are only called in one or two places and having the
ops structure exposed in the calls doesn't really matter much for readability etc.

> +}
> +
> +static inline int sps30_stop_meas(struct sps30_state *state)
> +{
> +	return state->ops->stop_meas(state);
> +}
> +
> +static inline int sps30_read_meas(struct sps30_state *state, void *meas, int num)
> +{
> +	return state->ops->read_meas(state, meas, num);
> +}
> +
> +static inline int sps30_clean_fan(struct sps30_state *state)
> +{
> +	return state->ops->clean_fan(state);
> +}
> +
> +static inline int sps30_write_cleaning_period(struct sps30_state *state, int period)
> +{
> +	return state->ops->write_cleaning_period(state, period);
> +}
> +
> +static inline int sps30_read_cleaning_period(struct sps30_state *state, int *period)
> +{
> +	return state->ops->read_cleaning_period(state, period);
> +}
> +
> +static inline int sps30_show_info(struct sps30_state *state)
> +{
> +	return state->ops->show_info(state);
> +}
> +
> +static inline int sps30_reset(struct sps30_state *state)
> +{
> +	return state->ops->reset(state);
> +}
> +
> +#endif
> diff --git a/drivers/iio/chemical/sps30_i2c.c b/drivers/iio/chemical/sps30_i2c.c
> new file mode 100644
> index 000000000000..97146cd50aa5
> --- /dev/null
> +++ b/drivers/iio/chemical/sps30_i2c.c
> @@ -0,0 +1,256 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Sensirion SPS30 particulate matter sensor i2c driver
> + *
> + * Copyright (c) 2020 Tomasz Duszynski <tomasz.duszynski@octakon.com>
> + *
> + * I2C slave address: 0x69
> + */
> +#include <asm/unaligned.h>
> +#include <linux/crc8.h>
> +#include <linux/delay.h>
> +#include <linux/device.h>
> +#include <linux/errno.h>
> +#include <linux/i2c.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/types.h>
> +
> +#include "sps30.h"
> +
> +#define SPS30_I2C_CRC8_POLYNOMIAL 0x31
> +/* max number of bytes needed to store PM measurements or serial string */
> +#define SPS30_I2C_MAX_BUF_SIZE 48
> +
> +DECLARE_CRC8_TABLE(sps30_i2c_crc8_table);
> +
> +#define SPS30_I2C_START_MEAS 0x0010
> +#define SPS30_I2C_STOP_MEAS 0x0104
> +#define SPS30_I2C_READ_MEAS 0x0300
> +#define SPS30_I2C_MEAS_READY 0x0202
> +#define SPS30_I2C_RESET 0xd304
> +#define SPS30_I2C_CLEAN_FAN 0x5607
> +#define SPS30_I2C_PERIOD 0x8004
> +#define SPS30_I2C_READ_SERIAL 0xd033
> +#define SPS30_I2C_READ_VERSION 0xd100
> +
> +static int sps30_i2c_xfer(struct sps30_state *state, char *txbuf, int txsize,
> +			  char *rxbuf, int rxsize)
> +{
> +	struct i2c_client *client = to_i2c_client(state->dev);
> +	int ret;
> +
> +	/*
> +	 * Sensor does not support repeated start so instead of
> +	 * sending two i2c messages in a row we just send one by one.
> +	 */
> +	ret = i2c_master_send(client, txbuf, txsize);
> +	if (ret < 0)
> +		return ret;
> +	if (ret != txsize)
> +		return -EIO;
> +
> +	if (!rxsize)
> +		return 0;
> +
> +	ret = i2c_master_recv(client, rxbuf, rxsize);
> +	if (ret < 0)
> +		return ret;
> +	if (ret != rxsize)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +static int sps30_i2c_command(struct sps30_state *state, u16 cmd, void *arg, int arg_size,
> +			     void *rsp, int rsp_size)
> +{
> +	/*
> +	 * Internally sensor stores measurements in a following manner:
> +	 *
> +	 * PM1: upper two bytes, crc8, lower two bytes, crc8
> +	 * PM2P5: upper two bytes, crc8, lower two bytes, crc8
> +	 * PM4: upper two bytes, crc8, lower two bytes, crc8
> +	 * PM10: upper two bytes, crc8, lower two bytes, crc8
> +	 *
> +	 * What follows next are number concentration measurements and
> +	 * typical particle size measurement which we omit.
> +	 */
> +	char buf[SPS30_I2C_MAX_BUF_SIZE];
> +	int i, ret;
> +	char *tmp;
> +	char crc;
> +
> +	put_unaligned_be16(cmd, buf);
> +	i = 2;
> +
> +	if (rsp) {
> +		/* each two bytes are followed by a crc8 */
> +		rsp_size += rsp_size / 2;
> +	} else {
> +		tmp = arg;
> +
> +		while (arg_size) {
> +			buf[i] = *tmp++;
> +			buf[i + 1] = *tmp++;
> +			buf[i + 2] = crc8(sps30_i2c_crc8_table, buf + i, 2, CRC8_INIT_VALUE);
> +			arg_size -= 2;
> +			i += 3;
> +		}
> +	}
> +
> +	ret = sps30_i2c_xfer(state, buf, i, buf, rsp_size);
> +	if (ret)
> +		return ret;
> +
> +	/* validate received data and strip off crc bytes */
> +	tmp = rsp;
> +	for (i = 0; i < rsp_size; i += 3) {
> +		crc = crc8(sps30_i2c_crc8_table, buf + i, 2, CRC8_INIT_VALUE);
> +		if (crc != buf[i + 2]) {
> +			dev_err(state->dev, "data integrity check failed\n");
> +			return -EIO;
> +		}
> +
> +		*tmp++ = buf[i];
> +		*tmp++ = buf[i + 1];
> +	}
> +
> +	return 0;
> +}
> +
> +static int sps30_i2c_start_meas(struct sps30_state *state)
> +{
> +	/* request BE IEEE754 formatted data */
> +	char buf[] = { 0x03, 0x00 };
> +
> +	return sps30_i2c_command(state, SPS30_I2C_START_MEAS, buf, sizeof(buf), NULL, 0);
> +}
> +
> +static int sps30_i2c_stop_meas(struct sps30_state *state)
> +{
> +	return sps30_i2c_command(state, SPS30_I2C_STOP_MEAS, NULL, 0, NULL, 0);
> +}
> +
> +static int sps30_i2c_reset(struct sps30_state *state)
> +{
> +	int ret;
> +
> +	ret = sps30_i2c_command(state, SPS30_I2C_RESET, NULL, 0, NULL, 0);
> +	msleep(500);
> +	/*
> +	 * Power-on-reset causes sensor to produce some glitch on i2c bus and
> +	 * some controllers end up in error state. Recover simply by placing
> +	 * some data on the bus, for example STOP_MEAS command, which
> +	 * is NOP in this case.
> +	 */
> +	sps30_i2c_stop_meas(state);
> +
> +	return ret;
> +}
> +
> +static bool sps30_i2c_meas_ready(struct sps30_state *state)
> +{
> +	char buf[2];
> +	int ret;
> +
> +	ret = sps30_i2c_command(state, SPS30_I2C_MEAS_READY, NULL, 0, buf, sizeof(buf));
> +	if (ret)
> +		return false;
> +
> +	return buf[1];
> +}
> +
> +static int sps30_i2c_read_meas(struct sps30_state *state, int *meas, int num)
> +{
> +	int tries = 3;
> +
> +	do {
> +		if (sps30_i2c_meas_ready(state))
> +			break;
> +
> +		if (msleep_interruptible(500))
> +			return -EINTR;
> +	} while (--tries);
> +
> +	if (!tries)
> +		return -ETIMEDOUT;
> +
> +	return sps30_i2c_command(state, SPS30_I2C_READ_MEAS, NULL, 0, meas, sizeof(num) * num);
> +}
> +
> +static int sps30_i2c_clean_fan(struct sps30_state *state)
> +{
> +	return sps30_i2c_command(state, SPS30_I2C_CLEAN_FAN, NULL, 0, NULL, 0);
> +}
> +
> +static int sps30_i2c_read_cleaning_period(struct sps30_state *state, int *period)
> +{
> +	return sps30_i2c_command(state, SPS30_I2C_PERIOD, NULL, 0, period, sizeof(*period));

Do you not want a fixed size type of period?  u32 or something like that?

> +}
> +
> +static int sps30_i2c_write_cleaning_period(struct sps30_state *state, int period)
> +{
> +	return sps30_i2c_command(state, SPS30_I2C_PERIOD, &period, sizeof(period), NULL, 0);
> +}
> +
> +static int sps30_i2c_show_info(struct sps30_state *state)
> +{
> +	/* extra nul just in case */
> +	char buf[32 + 1] = { 0x00 };
> +	int ret;
> +
> +	ret = sps30_i2c_command(state, SPS30_I2C_READ_SERIAL, NULL, 0, buf, sizeof(buf) - 1);
> +	if (ret)
> +		return ret;
> +
> +	dev_info(state->dev, "serial number: %s\n", buf);
> +
> +	ret = sps30_i2c_command(state, SPS30_I2C_READ_VERSION, NULL, 0, buf, 2);
> +	if (ret)
> +		return ret;
> +
> +	dev_info(state->dev, "fw version: %u.%u\n", buf[0], buf[1]);
> +
> +	return 0;
> +}
> +
> +static const struct sps30_ops sps30_i2c_ops = {
> +	.start_meas = sps30_i2c_start_meas,
> +	.stop_meas = sps30_i2c_stop_meas,
> +	.read_meas = sps30_i2c_read_meas,
> +	.reset = sps30_i2c_reset,
> +	.clean_fan = sps30_i2c_clean_fan,
> +	.read_cleaning_period = sps30_i2c_read_cleaning_period,
> +	.write_cleaning_period = sps30_i2c_write_cleaning_period,
> +	.show_info = sps30_i2c_show_info,
> +};
> +
> +static int sps30_i2c_probe(struct i2c_client *client)
> +{
> +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> +		return -EOPNOTSUPP;
> +
> +	crc8_populate_msb(sps30_i2c_crc8_table, SPS30_I2C_CRC8_POLYNOMIAL);
> +
> +	return sps30_probe(&client->dev, client->name, NULL, &sps30_i2c_ops);
> +}
> +
> +static const struct of_device_id sps30_i2c_of_match[] = {
> +	{ .compatible = "sensirion,sps30" },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, sps30_i2c_of_match);
> +
> +static struct i2c_driver sps30_i2c_driver = {
> +	.driver = {
> +		.name = KBUILD_MODNAME,
> +		.of_match_table = sps30_i2c_of_match,
> +	},
> +	.probe_new = sps30_i2c_probe,
> +};
> +module_i2c_driver(sps30_i2c_driver);
> +
> +MODULE_AUTHOR("Tomasz Duszynski <tomasz.duszynski@octakon.com>");
> +MODULE_DESCRIPTION("Sensirion SPS30 particulate matter sensor i2c driver");
> +MODULE_LICENSE("GPL v2");