Re: [PATCH v4] iio: chemical: scd30: Replace manual locking with RAII locking

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 23 May 2026 13:25:32 -0500
Maxwell Doose <m32285159@gmail.com> wrote:

> scd30_core.c currently uses manual mutex_lock() and mutex_unlock()
> calls. Replace them with the newer guard(mutex)() for cleaner RAII
> patterns and to improve maintainability.
> 
> Add new helper function scd30_trigger_handler_helper_locked() containing
> the critical section for scd30_trigger_handler(). After moving
> scd30_trigger_handler()'s critical section into the new helper, tune up
> control logic to return ret early and not memcpy() if it's an error
> condition.
> 
> In addition, small refactor to replace "?:" operator with regular
> if/else returns.
> 
> Signed-off-by: Maxwell Doose <m32285159@gmail.com>
Just some naming things inline.

I thought about just changing them and applying but decided
I'd rather you took another look to make sure you agree
with the suggested changes (and if you do send me a v5)

Thanks,

Jonathan

>  static ssize_t calibration_forced_value_store(struct device *dev, struct device_attribute *attr,
> @@ -424,11 +430,13 @@ static ssize_t calibration_forced_value_store(struct device *dev, struct device_
>  	if (val < SCD30_FRC_MIN_PPM || val > SCD30_FRC_MAX_PPM)
>  		return -EINVAL;
>  
> -	mutex_lock(&state->lock);
> -	ret = scd30_command_write(state, CMD_FRC, val);
> -	mutex_unlock(&state->lock);
> +	guard(mutex)(&state->lock);
>  
> -	return ret ?: len;
> +	ret = scd30_command_write(state, CMD_FRC, val);
> +	if (ret)
> +		return ret;
> +
> +	return len;
>  }
>  
>  static IIO_DEVICE_ATTR_RO(sampling_frequency_available, 0);
> @@ -579,24 +587,36 @@ static irqreturn_t scd30_irq_thread_handler(int irq, void *priv)
>  	return IRQ_HANDLED;
>  }
>  
> +/* Meant ONLY for scd30_trigger_handler() */

No need to say this in a comment. The code naming is clear enough. However...

> +static int scd30_trigger_handler_helper_locked(struct iio_dev *indio_dev,
> +					       int *scan_data, int arr_size)

Avoid using _locked() in naming.  It isn't clear to readers if that
means it is locked already, or will lock..  Also somewhat unnecessary
here. We don't need the function name to say why there is a helper.

arr_size would normally mean array size - i.e. how many ints
there are in scan_data.  Here it is the size of scan_data - probably
also make it a size_t

So this whole thing becomes

static int scd30_trigger_handler_helper(struct iio_dev *indio_dev,
					int *scan_data, size_t scan_data_size)





> +{
> +	struct scd30_state *state = iio_priv(indio_dev);
> +	int ret;
> +
> +	guard(mutex)(&state->lock);
> +
> +	if (!iio_trigger_using_own(indio_dev))
> +		ret = scd30_read_poll(state);
> +	else
> +		ret = scd30_read_meas(state);
> +	if (ret)
> +		return ret;
> +	memcpy(scan_data, state->meas, arr_size);
> +	return 0;
> +}
> +
>  static irqreturn_t scd30_trigger_handler(int irq, void *p)
>  {
>  	struct iio_poll_func *pf = p;
>  	struct iio_dev *indio_dev = pf->indio_dev;
> -	struct scd30_state *state = iio_priv(indio_dev);
>  	struct {
>  		int data[SCD30_MEAS_COUNT];
>  		aligned_s64 ts;
>  	} scan = { };
>  	int ret;
>  
> -	mutex_lock(&state->lock);
> -	if (!iio_trigger_using_own(indio_dev))
> -		ret = scd30_read_poll(state);
> -	else
> -		ret = scd30_read_meas(state);
> -	memcpy(scan.data, state->meas, sizeof(state->meas));
> -	mutex_unlock(&state->lock);
> +	ret = scd30_trigger_handler_helper_locked(indio_dev, scan.data, sizeof(scan.data));
>  	if (ret)
>  		goto out;
>