Re: [PATCH v3 3/4] drivers: iio: chemical: Add support for Sensirion SCD4x CO2 sensor

[Roan van Dijk]

On 25-09-2021 18:23, Jonathan Cameron wrote:
> On Wed, 22 Sep 2021 12:39:24 +0200
> Roan van Dijk <roan@xxxxxxxxxxx> wrote:
>
> > This is a driver for the SCD4x CO2 sensor from Sensirion. The sensor is
> > able to measure CO2 concentration, temperature and relative humdity.
> > The sensor uses a photoacoustic principle for measuring CO2 concentration.
> > An I2C interface is supported by this driver in order to communicate with
> > the sensor.
> >
> > Signed-off-by: Roan van Dijk <roan@xxxxxxxxxxx>
>
> Hi Roan,
>
> Only thing in here of significance is that the format for available attribute
> is wrong + it needs adding to the ABI docs.
>
> Given we are going to have a v4, I noted a few other minor things to tidy up.
>
> Thanks,
>
> Jonathan

Thank you for your feedback. I will make a new patch with these fixes.

The documentation for the _available and the fixes you suggested, have 
already been added in patch [PATCH v3 4/4]. Do I still need to add 
something to the ABI documentation or is it fine like this?

However, I will change the KernelVersion to 5.15 of the _available 
description in patch v4. I left this at 5.8 and that's not right, 
because this information is newly added.

Thanks,

Roan

> > +static int scd4x_read(struct scd4x_state *state, enum scd4x_cmd cmd,
> > +			void *response, int response_sz)
> > +{
> > +	struct i2c_client *client = state->client;
> > +	char buf[SCD4X_READ_BUF_SIZE];
> > +	char *rsp = response;
> > +	int i, ret;
> > +	char crc;
> > +
> > +	/*
> > +	 * Measurement needs to be stopped before sending commands.
> > +	 * Except for reading measurement and data ready command.
> > +	 */
> > +	if ((cmd != CMD_GET_DATA_READY) && (cmd != CMD_READ_MEAS)) {
> > +		ret = scd4x_send_command(state, CMD_STOP_MEAS);
> > +		if (ret)
> > +			return ret;
> > +
> > +		/* execution time for stopping measurement */
> > +		msleep_interruptible(500);
> > +	}
> > +
> > +	/*CRC byte for every 2 bytes of data */
>
> /* CRC..
>
> Please check for similar as otherwise we'll get 'cleanup' patches the moment various
> scripts hit this new code and it'll waste our time!
>
> > +	response_sz += response_sz / 2;
> > +
> > +	put_unaligned_be16(cmd, buf);
> > +	ret = scd4x_i2c_xfer(state, buf, 2, buf, response_sz);
> > +	if (ret)
> > +		return ret;
> > +
> > +	for (i = 0; i < response_sz; i += 3) {
> > +		crc = crc8(scd4x_crc8_table, buf + i, 2, CRC8_INIT_VALUE);
> > +		if (crc != buf[i + 2]) {
> > +			dev_err(&client->dev, "CRC error\n");
> > +			return -EIO;
> > +		}
> > +
> > +		*rsp++ = buf[i];
> > +		*rsp++ = buf[i + 1];
> > +	}
> > +
> > +	/* start measurement */
> > +	if ((cmd != CMD_GET_DATA_READY) && (cmd != CMD_READ_MEAS)) {
> > +		ret = scd4x_send_command(state, CMD_START_MEAS);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
>
> ...
>
> > +
> > +static IIO_DEVICE_ATTR_RW(calibration_auto_enable, 0);
> > +static IIO_DEVICE_ATTR_WO(calibration_forced_value, 0);
> > +
> > +static IIO_CONST_ATTR(calibration_forced_value_available,
> > +	       __stringify(SCD4X_FRC_MIN_PPM 1 SCD4X_FRC_MAX_PPM));
>
> Ah, I wasn't completely clear on this.  See the main ABI doc for
> _available
>
> Format for this needs to include brackets to indicate it's a range
> rather than 3 numbers
> "[MIN 1  MAX]"
>
>
> Having added this it also needs to be in the ABI documentation.
> Whilst somewhat trivial, all ABI should be documented there.
>
> > +
> > +static struct attribute *scd4x_attrs[] = {
> > +	&iio_dev_attr_calibration_auto_enable.dev_attr.attr,
> > +	&iio_dev_attr_calibration_forced_value.dev_attr.attr,
> > +	&iio_const_attr_calibration_forced_value_available.dev_attr.attr,
> > +	NULL
> > +};
> > +
> > +static const struct attribute_group scd4x_attr_group = {
> > +	.attrs = scd4x_attrs,
> > +};
> > +
> > +static const struct iio_info scd4x_info = {
> > +	.attrs = &scd4x_attr_group,
> > +	.read_raw = scd4x_read_raw,
> > +	.write_raw = scd4x_write_raw,
> > +};
> > +
>
> ...
>
> > +
> > +static irqreturn_t scd4x_trigger_handler(int irq, void *p)
> > +{
> > +	struct iio_poll_func *pf = p;
> > +	struct iio_dev *indio_dev = pf->indio_dev;
> > +	struct scd4x_state *state = iio_priv(indio_dev);
> > +	struct {
> > +		uint16_t data[3];
> > +		int64_t ts __aligned(8);
> > +	} scan;
> > +	int ret;
> > +	uint16_t buf[3];
> > +
> > +	mutex_lock(&state->lock);
> > +	ret = scd4x_read_poll(state, buf);
> > +	mutex_unlock(&state->lock);
> > +	if (ret)
> > +		goto out;
> > +
> > +	memset(&scan, 0, sizeof(scan));
> > +	memcpy(scan.data, buf, sizeof(buf));
>
> I missed this before, but why not do the scd4x_read_poll() directly into scan->data after
> you've done the memset?  That way you avoid the need for a memcpy.
>
> i.e.
>
> 	memset(&scan, 0, sizeof(scan));
> 	mutex_lock(&state->lock)
> 	ret = scd4x_read_poll(state, scan->data);
> 	mutex_unlock(&state->lock);
> 	if (ret)
> 	...
>
>
> > +
> > +	iio_push_to_buffers_with_timestamp(indio_dev, &scan, iio_get_time_ns(indio_dev));
> > +out:
> > +	iio_trigger_notify_done(indio_dev->trig);
> > +	return IRQ_HANDLED;
> > +}
> > +