linux-kernel - Re: [PATCH] iio: stm32-dac: Replace indio

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Date:   Mon, 18 May 2020 11:22:40 +0200
From:   Fabrice Gasnier <fabrice.gasnier@...com>
To:     Jonathan Cameron <jic23@...nel.org>,
        Sergiu Cuciurean <sergiu.cuciurean@...log.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-iio@...r.kernel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] iio: stm32-dac: Replace indio_dev->mlock with own device
 lock

On 5/16/20 5:35 PM, Jonathan Cameron wrote:
> On Thu, 14 May 2020 11:50:12 +0300
> Sergiu Cuciurean <sergiu.cuciurean@...log.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@...log.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.

Hi Sergiu,

Indeed, purpose is to protect against a race here when reading CR, and
updating it via regmap (this also makes the subsequent pm_runtime calls
to be balanced based on this).
(Side note: there is no data buffer involved for the DAC.)
Could you please update the comment ?

Thanks,
Fabrice

> 
> 
>>   */
>>  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;
>