Re: [PATCH v2 01/16] iio: adc: ad799x: do not use internal iio_dev lock

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 4 Oct 2022 15:48:54 +0200
Nuno Sá <nuno.sa@analog.com> wrote:

> 'mlock' was being grabbed when setting the device frequency. In order to
> not introduce any functional change a new lock is added. With that in
> mind, the lock also needs to be grabbed in the places where 'mlock' is
> since it was also being used to protect st->config against the current
> device state.
> 
> On the other places the lock was being used, we can just drop
> it since we are only doing one i2c bus read/write which is already
> safe.
> 
> While at it, properly include "mutex.h" for mutex related APIs.
> 
> Signed-off-by: Nuno Sá <nuno.sa@analog.com>
In interests of cutting down scope of any future versions
(Should there need to be anyway) I'm going to pick up the non controversial
patches.

Applied to the togreg branch of iio.git though that's only pushed out
as testing for now as we are mid merge window.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/ad799x.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad799x.c b/drivers/iio/adc/ad799x.c
> index 262bd7665b33..44f7a80a0749 100644
> --- a/drivers/iio/adc/ad799x.c
> +++ b/drivers/iio/adc/ad799x.c
> @@ -28,6 +28,7 @@
>  #include <linux/types.h>
>  #include <linux/err.h>
>  #include <linux/module.h>
> +#include <linux/mutex.h>
>  #include <linux/bitops.h>
>  
>  #include <linux/iio/iio.h>
> @@ -125,6 +126,8 @@ struct ad799x_state {
>  	const struct ad799x_chip_config	*chip_config;
>  	struct regulator		*reg;
>  	struct regulator		*vref;
> +	/* lock to protect against multiple access to the device */
> +	struct mutex			lock;
>  	unsigned			id;
>  	u16				config;
>  
> @@ -290,7 +293,9 @@ static int ad799x_read_raw(struct iio_dev *indio_dev,
>  		ret = iio_device_claim_direct_mode(indio_dev);
>  		if (ret)
>  			return ret;
> +		mutex_lock(&st->lock);
>  		ret = ad799x_scan_direct(st, chan->scan_index);
> +		mutex_unlock(&st->lock);
>  		iio_device_release_direct_mode(indio_dev);
>  
>  		if (ret < 0)
> @@ -351,7 +356,8 @@ static ssize_t ad799x_write_frequency(struct device *dev,
>  	if (ret)
>  		return ret;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&st->lock);
> +
>  	ret = i2c_smbus_read_byte_data(st->client, AD7998_CYCLE_TMR_REG);
>  	if (ret < 0)
>  		goto error_ret_mutex;
> @@ -373,7 +379,7 @@ static ssize_t ad799x_write_frequency(struct device *dev,
>  	ret = len;
>  
>  error_ret_mutex:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->lock);
>  
>  	return ret;
>  }
> @@ -407,6 +413,8 @@ static int ad799x_write_event_config(struct iio_dev *indio_dev,
>  	if (ret)
>  		return ret;
>  
> +	mutex_lock(&st->lock);
> +
>  	if (state)
>  		st->config |= BIT(chan->scan_index) << AD799X_CHANNEL_SHIFT;
>  	else
> @@ -418,6 +426,7 @@ static int ad799x_write_event_config(struct iio_dev *indio_dev,
>  		st->config &= ~AD7998_ALERT_EN;
>  
>  	ret = ad799x_write_config(st, st->config);
> +	mutex_unlock(&st->lock);
>  	iio_device_release_direct_mode(indio_dev);
>  	return ret;
>  }
> @@ -454,11 +463,9 @@ static int ad799x_write_event_value(struct iio_dev *indio_dev,
>  	if (val < 0 || val > GENMASK(chan->scan_type.realbits - 1, 0))
>  		return -EINVAL;
>  
> -	mutex_lock(&indio_dev->mlock);
>  	ret = i2c_smbus_write_word_swapped(st->client,
>  		ad799x_threshold_reg(chan, dir, info),
>  		val << chan->scan_type.shift);
> -	mutex_unlock(&indio_dev->mlock);
>  
>  	return ret;
>  }
> @@ -473,10 +480,8 @@ static int ad799x_read_event_value(struct iio_dev *indio_dev,
>  	int ret;
>  	struct ad799x_state *st = iio_priv(indio_dev);
>  
> -	mutex_lock(&indio_dev->mlock);
>  	ret = i2c_smbus_read_word_swapped(st->client,
>  		ad799x_threshold_reg(chan, dir, info));
> -	mutex_unlock(&indio_dev->mlock);
>  	if (ret < 0)
>  		return ret;
>  	*val = (ret >> chan->scan_type.shift) &
> @@ -863,6 +868,9 @@ static int ad799x_probe(struct i2c_client *client,
>  		if (ret)
>  			goto error_cleanup_ring;
>  	}
> +
> +	mutex_init(&st->lock);
> +
>  	ret = iio_device_register(indio_dev);
>  	if (ret)
>  		goto error_cleanup_ring;


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