Re: [PATCH v4 17/17] staging: iio: resolver: ad2s1210: simplify code with guard(mutex)

[Jonathan Cameron <jic23@kernel.org>]

On Thu,  5 Oct 2023 19:50:34 -0500
David Lechner <dlechner@baylibre.com> wrote:

> We can simplify the code and get rid of most of the gotos by using
> guard(mutex) from cleanup.h.
You could consider scoped_guard() for a few cases in here, but perhaps
it's better to be consistent and always use the guard() version.

There is a small timing question wrt to the gpio manipulation inline.

> 
> Signed-off-by: David Lechner <dlechner@baylibre.com>
> ---
> 
> v4 changes: New patch in v4.
> 
>  drivers/staging/iio/resolver/ad2s1210.c | 157 ++++++++++----------------------
>  1 file changed, 50 insertions(+), 107 deletions(-)
> 
> diff --git a/drivers/staging/iio/resolver/ad2s1210.c b/drivers/staging/iio/resolver/ad2s1210.c
> index c4e1bc22e8b0..c4e0ffa92dc2 100644
> --- a/drivers/staging/iio/resolver/ad2s1210.c
> +++ b/drivers/staging/iio/resolver/ad2s1210.c
> @@ -47,6 +47,7 @@
>  
>  #include <linux/bitfield.h>
>  #include <linux/bits.h>
> +#include <linux/cleanup.h>
>  #include <linux/clk.h>
>  #include <linux/delay.h>
>  #include <linux/device.h>
> @@ -404,11 +405,13 @@ static int ad2s1210_single_conversion(struct iio_dev *indio_dev,
>  	s64 timestamp;
>  	int ret;
>  
> -	mutex_lock(&st->lock);
> +	guard(mutex)(&st->lock);
> +
>  	gpiod_set_value(st->sample_gpio, 1);
>  	timestamp = iio_get_time_ns(indio_dev);
>  	/* delay (6 * tck + 20) nano seconds */
>  	udelay(1);
> +	gpiod_set_value(st->sample_gpio, 0);
>  
>  	switch (chan->type) {
>  	case IIO_ANGL:
> @@ -418,14 +421,13 @@ static int ad2s1210_single_conversion(struct iio_dev *indio_dev,
>  		ret = ad2s1210_set_mode(st, MOD_VEL);
>  		break;
>  	default:
> -		ret = -EINVAL;
> -		break;
> +		return -EINVAL;
>  	}
>  	if (ret < 0)
> -		goto error_ret;
> +		return ret;
>  	ret = spi_read(st->sdev, &st->sample, 3);
>  	if (ret < 0)
> -		goto error_ret;
> +		return ret;
>  
>  	switch (chan->type) {
>  	case IIO_ANGL:
> @@ -437,17 +439,11 @@ static int ad2s1210_single_conversion(struct iio_dev *indio_dev,
>  		ret = IIO_VAL_INT;
>  		break;
>  	default:
> -		ret = -EINVAL;
> -		break;
> +		return -EINVAL;
>  	}
>  
>  	ad2s1210_push_events(indio_dev, st->sample.fault, timestamp);
>  
> -error_ret:
> -	gpiod_set_value(st->sample_gpio, 0);
> -	/* delay (2 * tck + 20) nano seconds */
> -	udelay(1);

Dropping this delay isn't obviously safe (though it probably is given stuff done before we exit).
I assume there are no rules on holding the gpio down for the register read.
 
If nothing else I think the patch description needs to made an argument for why it is fine.

> -	mutex_unlock(&st->lock);
>  	return ret;
>  }
>