linux-kernel - Re: [PATCH v3 3/3] staging: iio: ad9832: Add minor improvements to ad9832_write

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Message-ID: <20250421124044.400628f1@jic23-huawei>
Date: Mon, 21 Apr 2025 12:40:44 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Gabriel Shahrouzi <gshahrouzi@...il.com>
Cc: gregkh@...uxfoundation.org, lars@...afoo.de, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-staging@...ts.linux.dev,
 Michael.Hennerich@...log.com, skhan@...uxfoundation.org,
 linux-kernel-mentees@...ts.linux.dev
Subject: Re: [PATCH v3 3/3] staging: iio: ad9832: Add minor improvements to
 ad9832_write_powerdown

On Sun, 20 Apr 2025 13:54:19 -0400
Gabriel Shahrouzi <gshahrouzi@...il.com> wrote:

> Minimize size of type that needs to be used by replacing unsigned long
> with bool. Avoid redundancy by checking if cached power state is the
> same as the one requested.
> 
> Signed-off-by: Gabriel Shahrouzi <gshahrouzi@...il.com>
> ---
>  drivers/staging/iio/frequency/ad9832.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/staging/iio/frequency/ad9832.c b/drivers/staging/iio/frequency/ad9832.c
> index a8fc20379efed..2ab6026d56b5c 100644
> --- a/drivers/staging/iio/frequency/ad9832.c
> +++ b/drivers/staging/iio/frequency/ad9832.c
> @@ -173,13 +173,19 @@ static ssize_t ad9832_write_powerdown(struct device *dev, struct device_attribut
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct ad9832_state *st = iio_priv(indio_dev);
>  	int ret;
> -	unsigned long val;
> +	bool val;
> +	bool cur;
>  
> -	ret = kstrtoul(buf, 10, &val);
> +	ret = kstrtobool(buf, &val);
That could have been done in the previous patch as you are changing the ABI anyway.
>  	if (ret)
> -		goto error_ret;
> +		return ret;
>  
>  	mutex_lock(&st->lock);
> +
> +	cur = !!(st->ctrl_src & AD9832_SLEEP);

Worth thinking about whether this driver will ever be converted to regmap with regcache.
If that's a reasonable thing to do long term this sort of optimization adds nothing
useful as we'll skip the right anwyay if the driver is already in the appropriate state.

This isn't a high performance path, so I'd not bother with the check for now.

> +	if (val == cur)
> +		goto unlock;
> +
>  	if (val)
>  		st->ctrl_src |= AD9832_SLEEP;
>  	else
> @@ -189,10 +195,10 @@ static ssize_t ad9832_write_powerdown(struct device *dev, struct device_attribut
>  	st->data = cpu_to_be16((AD9832_CMD_SLEEPRESCLR << CMD_SHIFT) |
>  				st->ctrl_src);
>  	ret = spi_sync(st->spi, &st->msg);
If this fails, where doe ret end up? Looks to me like we now don't report the error
Anyhow, see guard() comment in previous patch.  These days we can avoid a lot of
this complexity by using that to allow direct returns where we first see the error.

> -	mutex_unlock(&st->lock);
>  
> -error_ret:
> -	return ret ? ret : len;
> +unlock:
> +	mutex_unlock(&st->lock);
> +	return len;
>  }
>  
>  static ssize_t ad9832_write(struct device *dev, struct device_attribute *attr,