linux-kernel - Re: [PATCH 2/5] staging: iio: ad9832: convert to guard(mutex)

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Message-ID: <aUQa0IBuE7EITq9G@Lewboski.localdomain>
Date: Thu, 18 Dec 2025 12:16:32 -0300
From: Tomas Borquez <tomasborquez13@...il.com>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>
Cc: Jonathan Cameron <jic23@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org, linux-staging@...ts.linux.dev
Subject: Re: [PATCH 2/5] staging: iio: ad9832: convert to guard(mutex)

On Thu, Dec 18, 2025 at 11:34:05AM -0300, Marcelo Schmitt wrote:
> On 12/15, Tomas Borquez wrote:
...
> > -	mutex_lock(&st->lock);
> > +	guard(mutex)(&st->lock);
> >  	switch ((u32)this_attr->address) {
> >  	case AD9832_FREQ0HM:
> >  	case AD9832_FREQ1HM:
> > @@ -203,22 +205,18 @@ static ssize_t ad9832_write(struct device *dev, struct device_attribute *attr,
> >  		ret = spi_sync(st->spi, &st->msg);
> >  		break;
> >  	case AD9832_FREQ_SYM:
> > -		if (val == 1 || val == 0) {
> > -			st->ctrl_fp &= ~AD9832_FREQ;
> > -			st->ctrl_fp |= FIELD_PREP(AD9832_FREQ, val ? 1 : 0);
> > -		} else {
> > -			ret = -EINVAL;
> > -			break;
> > -		}
> > +		if (val != 1 && val != 0)
> > +			return -EINVAL;
> > +
> > +		st->ctrl_fp &= ~AD9832_FREQ;
> > +		st->ctrl_fp |= FIELD_PREP(AD9832_FREQ, val ? 1 : 0);
> >  		st->data = cpu_to_be16(FIELD_PREP(AD9832_CMD_MSK, AD9832_CMD_FPSELECT) |
> >  						  st->ctrl_fp);
> >  		ret = spi_sync(st->spi, &st->msg);
> >  		break;
> Since we now have the mutex unlock handled by guard, why not returning directly
> from each case?
> E.g.
> 	case AD9832_FREQ1HM:
> -		ret = ad9832_write_frequency(st, this_attr->address, val);
> -		break;
> +		return ad9832_write_frequency(st, this_attr->address, val);
> I think the last return (outside the default clause) won't be needed anymore.
Wouldn't work because we need to return len too, so it would be more like:

 case AD9832_FREQ1HM:
		 ret = ad9832_write_frequency(st, this_attr->address, val);
+    return ret ?: len;

Which is a bit more repetitive than just returning at the end ret ?: len,
but lemme know what you think.

>
> And, since you are touching the lock, you may also update to use
> devm_mutex_init() (that would probably be best appreciated as a separate patch).

Yup, sounds good :)

Tomas