Re: [PATCH 1/3] iio: chemical: sgp40: Implement get_serial_number-command

["Maxwell Doose" <maxwell@maxwelld.cc>]

Hi there Jaakko,

Firstly a (rather important) question I have is what's the point? I'm
not sure that anyone will need the serial number on the fly (assuming a
business would be using this, they will likely keep records of their
parts). Though maybe I could be wrong (so feel free to prove me wrong).

On Fri Sep 18, 2026 at 8:40 AM CDT
Jaakko Koivisto <jmatko@utu.fi> wrote:

> -Retrieve the chip serial number.
> -Present the serial number to userspace as device attribute.
> -Rename the tg_measure -struct now that is is used for multiple
> commands.
>

Last one should be left out and put in a separate patch.

Also, commit message needs a bit of work, something like:
	"Add support to the SGP40 driver to enable retrieval of the
	serial number from the chip and add new sysfs attribute to
	expose the serial number to userspace."

> Signed-off-by: Jaakko Koivisto <jmatko@utu.fi>
> ---
>  drivers/iio/chemical/sgp40.c | 78 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 76 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iio/chemical/sgp40.c b/drivers/iio/chemical/sgp40.c
> index b2b5e32a9eb2..c1e2a992ec2a 100644
> --- a/drivers/iio/chemical/sgp40.c
> +++ b/drivers/iio/chemical/sgp40.c
> @@ -35,6 +35,7 @@
>  #include <linux/mutex.h>
>  #include <linux/i2c.h>
>  #include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
>  
>  /*
>   * floating point calculation of voc is done as integer
> @@ -53,11 +54,12 @@ struct sgp40_data {
>  	int			rht;
>  	int			temp;
>  	int			res_calibbias;
> +	u64			serial_number;
>  	/* Prevent concurrent access to rht, tmp, calibbias */
>  	struct mutex		lock;
>  };
>  
> -struct sgp40_tg_measure {
> +struct sgp40_command {
>  	u8	command[2];
>  	__be16	rht_ticks;
>  	u8	rht_crc;
> @@ -70,6 +72,18 @@ struct sgp40_tg_result {
>  	u8	res_crc;
>  } __packed;
>  

Name change should be put in a different patch or just left out
entirely.

> +/*
> + * Datasheet table 16. Serial number is given as 48-bit value 0xAAAABBBBCCCC.
> + */
> +struct sgp40_serial_number_result {
> +	__be16	A;
> +	u8	A_crc;
> +	__be16	B;
> +	u8	B_crc;
> +	__be16	C;
> +	u8	C_crc;
> +} __packed;
> +

Perhaps this but maybe this could be implemented as an
annonymous struct instead.

>  static const struct iio_chan_spec sgp40_channels[] = {
>  	{
>  		.type = IIO_CONCENTRATION,
> @@ -162,6 +176,40 @@ static int sgp40_calc_voc(struct sgp40_data *data, u16 resistance_raw, int *voc)
>  	return 0;
>  }
>  
> +static int sgp40_get_serial_number(struct sgp40_data *data)
> +{
> +	int ret;
> +	struct i2c_client *client = data->client;
> +	struct sgp40_command get_sn = {.command = {0x36, 0x82}};
> +	struct sgp40_serial_number_result res;
> +
> +	ret = i2c_master_send(client, (char*)&get_sn, sizeof(get_sn.command));
> +	if (ret != sizeof(get_sn.command)) {
> +		dev_err(data->dev, "i2c_master_send ret: %d, expected %zu", ret, sizeof(get_sn.command));

Missing '\n' here (sashiko).

> +		return -EIO;
> +	}
> +	msleep(1);
> +	ret = i2c_master_recv(client, (char*)&res, sizeof(res));
> +	if (ret < 0)
> +		return ret;
> +	if (ret != sizeof(res)) {
> +		dev_err(data->dev, "i2c_master_recv ret: %d, expected: %zu", ret, sizeof(res));
> +		return -EIO;
> +	}
> +
> +	if (crc8(sgp40_crc8_table, (u8*)&res.A, 2, SGP40_CRC8_INIT) != res.A_crc ||
> +	    crc8(sgp40_crc8_table, (u8*)&res.B, 2, SGP40_CRC8_INIT) != res.B_crc ||
> +	    crc8(sgp40_crc8_table, (u8*)&res.C, 2, SGP40_CRC8_INIT) != res.C_crc)
> +	{
> +		dev_warn(data->dev, "CRC error in get_serial_number");

Probably should return either -EIO or -EREMOTEIO here (sashiko).

> +	}
> +
> +	data->serial_number = 0LL | ((u64)be16_to_cpu(res.A) << 32) | ((u64)be16_to_cpu(res.B) << 16) | (u64)be16_to_cpu(res.C);
> +	dev_dbg(data->dev, "serial number: %llu", data->serial_number);
> +
> +	return 0;
> +}
> +
>  static int sgp40_measure_resistance_raw(struct sgp40_data *data, u16 *resistance_raw)
>  {
>  	int ret;
> @@ -169,7 +217,7 @@ static int sgp40_measure_resistance_raw(struct sgp40_data *data, u16 *resistance
>  	u32 ticks;
>  	u16 ticks16;
>  	u8 crc;
> -	struct sgp40_tg_measure tg = {.command = {0x26, 0x0F}};
> +	struct sgp40_command tg = {.command = {0x26, 0x0F}};
>  	struct sgp40_tg_result tgres;
>  
>  	mutex_lock(&data->lock);
> @@ -311,9 +359,31 @@ static int sgp40_write_raw(struct iio_dev *indio_dev,
>  	return -EINVAL;
>  }
>  
> +static ssize_t serial_number_show(struct device *dev,
> +				  struct device_attribute *attr,
> +				  char *buf)
> +{
> +	struct sgp40_data *data = iio_priv(dev_to_iio_dev(dev));
> +
> +	return sysfs_emit_at(buf, 0, "%llu\n", data->serial_number);
> +}
> +
> +static IIO_DEVICE_ATTR_RO(serial_number, 0);
> +
> +static struct attribute *sgp40_attributes[] = {
> +	&iio_dev_attr_serial_number.dev_attr.attr,
> +	NULL
> +};
> +
> +static struct attribute_group sgp40_attribute_group = {
> +	.attrs = sgp40_attributes,
> +};
> +
> +
>  static const struct iio_info sgp40_info = {
>  	.read_raw	= sgp40_read_raw,
>  	.write_raw	= sgp40_write_raw,
> +	.attrs		= &sgp40_attribute_group,
>  };
>  
>  static int sgp40_probe(struct i2c_client *client)
> @@ -347,6 +417,10 @@ static int sgp40_probe(struct i2c_client *client)
>  	indio_dev->channels = sgp40_channels;
>  	indio_dev->num_channels = ARRAY_SIZE(sgp40_channels);
>  
> +	ret = sgp40_get_serial_number(data);
> +	if (ret)
> +		dev_warn(dev, "failed to retrieve device serial number\n");
> +
>  	ret = devm_iio_device_register(dev, indio_dev);
>  	if (ret)
>  		dev_err(dev, "failed to register iio device\n");