Re: [PATCH v2] iio: stm32-dac: Replace indio_dev->mlock with own device lock

[Fabrice Gasnier]

On 9/16/20 11:23 AM, Alexandru Ardelean wrote:
> From: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx>
> 
> As part of the general cleanup of indio_dev->mlock, this change replaces
> it with a local lock. The lock protects against potential races when
> reading the CR reg and then updating, so that the state of pm_runtime
> is consistent between the two operations.
> 
> This is part of a bigger cleanup.
> Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@xxxxxxxxxxxxxx/
> 
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@xxxxxxxxxx>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
> ---
>  drivers/iio/dac/stm32-dac.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)

Hi Alexandru,

Many thanks for this updated patch,

Reviewed-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx>

Best regards,
Fabrice

> 
> diff --git a/drivers/iio/dac/stm32-dac.c b/drivers/iio/dac/stm32-dac.c
> index 092c796fa3d9..12dec68c16f7 100644
> --- a/drivers/iio/dac/stm32-dac.c
> +++ b/drivers/iio/dac/stm32-dac.c
> @@ -26,9 +26,12 @@
>  /**
>   * struct stm32_dac - private data of DAC driver
>   * @common:		reference to DAC common data
> + * @lock:		lock to protect against potential races when reading
> + *			and update CR, to keep it in sync with pm_runtime
>   */
>  struct stm32_dac {
>  	struct stm32_dac_common *common;
> +	struct mutex		lock;
>  };
>  
>  static int stm32_dac_is_enabled(struct iio_dev *indio_dev, int channel)
> @@ -58,10 +61,10 @@ static int stm32_dac_set_enable_state(struct iio_dev *indio_dev, int ch,
>  	int ret;
>  
>  	/* already enabled / disabled ? */
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&dac->lock);
>  	ret = stm32_dac_is_enabled(indio_dev, ch);
>  	if (ret < 0 || enable == !!ret) {
> -		mutex_unlock(&indio_dev->mlock);
> +		mutex_unlock(&dac->lock);
>  		return ret < 0 ? ret : 0;
>  	}
>  
> @@ -69,13 +72,13 @@ static int stm32_dac_set_enable_state(struct iio_dev *indio_dev, int ch,
>  		ret = pm_runtime_get_sync(dev);
>  		if (ret < 0) {
>  			pm_runtime_put_noidle(dev);
> -			mutex_unlock(&indio_dev->mlock);
> +			mutex_unlock(&dac->lock);
>  			return ret;
>  		}
>  	}
>  
>  	ret = regmap_update_bits(dac->common->regmap, STM32_DAC_CR, msk, en);
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&dac->lock);
>  	if (ret < 0) {
>  		dev_err(&indio_dev->dev, "%s failed\n", en ?
>  			"Enable" : "Disable");
> @@ -327,6 +330,8 @@ static int stm32_dac_probe(struct platform_device *pdev)
>  	indio_dev->info = &stm32_dac_iio_info;
>  	indio_dev->modes = INDIO_DIRECT_MODE;
>  
> +	mutex_init(&dac->lock);
> +
>  	ret = stm32_dac_chan_of_init(indio_dev);
>  	if (ret < 0)
>  		return ret;
>