linux-kernel - Re: [PATCH v2] iio: stm32-dac: Replace indio

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Message-ID: <CA+U=DsrMDSTQKEc2_3+W8u4bLraAowVB3nB4huKY--v8gnds2Q@mail.gmail.com>
Date:   Thu, 27 Aug 2020 11:55:37 +0300
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     linux-iio <linux-iio@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Jonathan Cameron <jic23@...nel.org>, alexandre.torgue@...com,
        Fabrice Gasnier <fabrice.gasnier@...com>,
        Sergiu Cuciurean <sergiu.cuciurean@...log.com>
Subject: Re: [PATCH v2] iio: stm32-dac: Replace indio_dev->mlock with own
 device lock

On Wed, Aug 26, 2020 at 3:03 PM Alexandru Ardelean
<alexandru.ardelean@...log.com> wrote:
>
> From: Sergiu Cuciurean <sergiu.cuciurean@...log.com>
>
> 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.
>
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@...log.com>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
> ---

Forgot the changelog here.
Apologies.

Changelog v1 -> v2:
* removed whitespace change for 'common' field
* updated comment about the lock usage

>  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 092c796fa3d9..7a8aed476850 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
>   */
>  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");
> @@ -327,6 +329,8 @@ 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;
> --
> 2.25.1
>