Re: [PATCH 2/2] iio: chemical: Add driver support for sgp40

[Guenter Roeck]

On 7/31/21 9:39 AM, Jonathan Cameron wrote:
> On Tue, 27 Jul 2021 18:35:19 +0200
> Andreas Klinger <ak@xxxxxxxxxxxxx> wrote:
>
> > sgp40 is a gas sensor used for measuring the air quality.
> >
> > This driver is reading the raw resistance value which can be passed to
> > a userspace algorithm for further calculation.
> >
> > The raw value is also used to calculate an estimated absolute voc index
> > in the range from 0 to 500. For this purpose the raw_mean value of the
> > resistance for which the index value is 250 might be set up as a
> > calibration step.
> >
> > Compensation of relative humidity and temperature is supported and can
> > be used by writing to device attributes of the driver.
> >
> > There is a predecesor sensor type (sgp30) already existing. This driver
> > module was not extended because the new sensor is quite different in its
> > i2c telegrams.
> >
> > Signed-off-by: Andreas Klinger <ak@xxxxxxxxxxxxx>
>
> Hi Andreas,
>
> Non standard ABI in here, so we are missing documentation in Documentation/ABI/testing/sysfs-bus-iio-*
>
> Otherwise a few suggestions inline.
>
> Thanks,
>
> Jonathan
>
>
> > ---
[ ... ]

> > +static int sgp40_read_raw(struct iio_dev *indio_dev,
> > +			struct iio_chan_spec const *chan, int *val,
> > +			int *val2, long mask)
> > +{
> > +	struct sgp40_data *data = iio_priv(indio_dev);
> > +	int ret;
> > +	u16 raw;
> > +	int voc;
> > +
> > +	switch (mask) {
> > +	case IIO_CHAN_INFO_RAW:
> > +		mutex_lock(&data->lock);
> > +		ret = sgp40_measure_raw(data, &raw);
> > +		if (ret) {
> > +			mutex_unlock(&data->lock);
> > +			return ret;
> > +		}
> > +		*val = raw;
> > +		ret = IIO_VAL_INT;
> > +		mutex_unlock(&data->lock);
> > +		break;
> > +	case IIO_CHAN_INFO_PROCESSED:
> > +		mutex_lock(&data->lock);
> > +		ret = sgp40_measure_raw(data, &raw);
> > +		if (ret) {
> > +			mutex_unlock(&data->lock);
> > +			return ret;
> > +		}
> > +		ret = sgp40_calc_voc(data, raw, &voc);
> > +		if (ret) {
> > +			mutex_unlock(&data->lock);
> > +			return ret;
> > +		}
> > +		*val = voc;
> > +		ret = IIO_VAL_INT;
> > +		mutex_unlock(&data->lock);
>
> You are holding the lock longer than needed - it would be good
> to reduce this, hopefully removing the need for unlocking separately
> in each of the error paths.
>
> > +		break;
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +
> > +	return ret;
>
> Drop this as you can't get here.

Are you sure ? I see several "break;" above.

Guenter