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

From: Jonathan Cameron <jic23@kernel.org>
To: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Cc: <linux-kernel@vger.kernel.org>, <linux-iio@vger.kernel.org>,
	Hartmut Knaack <knaack.h@gmx.de>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Alexandre Torgue <alexandre.torgue@st.com>,
	Fabrice Gasnier <fabrice.gasnier@st.com>,
	<linux-stm32@st-md-mailman.stormreply.com>,
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] iio: stm32-dac: Replace indio_dev->mlock with own device lock
Date: Sat, 16 May 2020 16:35:21 +0100	[thread overview]
Message-ID: <20200516163521.2812cf86@archlinux> (raw)
In-Reply-To: <20200514085018.79948-1-sergiu.cuciurean@analog.com>

On Thu, 14 May 2020 11:50:12 +0300
Sergiu Cuciurean <sergiu.cuciurean@analog.com> wrote:

> As part of the general cleanup of indio_dev->mlock, this change replaces
> it with a local lock on the device's state structure.
> 
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> ---
>  drivers/iio/dac/stm32-dac.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/dac/stm32-dac.c b/drivers/iio/dac/stm32-dac.c
> index f22c1d9129b2..74b9474c8590 100644
> --- a/drivers/iio/dac/stm32-dac.c
> +++ b/drivers/iio/dac/stm32-dac.c
> @@ -26,9 +26,11 @@
>  /**
>   * struct stm32_dac - private data of DAC driver
>   * @common:		reference to DAC common data
> + * @lock: lock to protect the data buffer during regmap ops

In this particular case I'm not sure that's what mlock was being used for.
I think it's about avoiding races around checking if powered down and
actually doing it.

>   */
>  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 +60,10 @@ 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 +71,13 @@ 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");
> @@ -328,6 +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;