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

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Date:   Sat, 31 Jul 2021 11:06:25 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Jonathan Cameron <jic23@...nel.org>,
        Andreas Klinger <ak@...klinger.de>
Cc:     devicetree@...r.kernel.org, linux-iio@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Jiri Kosina <trivial@...nel.org>,
        Chris Packham <chris.packham@...iedtelesis.co.nz>,
        Slawomir Stepien <sst@...zta.fm>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Vadim Pasternak <vadimp@...dia.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        linux-kernel@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
        Tomasz Duszynski <tomasz.duszynski@...akon.com>
Subject: Re: [PATCH 2/2] iio: chemical: Add driver support for sgp40

On 7/31/21 9:39 AM, Jonathan Cameron wrote:
> On Tue, 27 Jul 2021 18:35:19 +0200
> Andreas Klinger <ak@...klinger.de> 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@...klinger.de>
> 
> 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