Re: [PATCH v2] iio: dac: ti-dac7612: Replace indio_dev->mlock with own device lock

[Jonathan Cameron]

On Wed, 16 Sep 2020 12:25:35 +0300
Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx> 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 on the device's state from potential concurrent write
> accesses from userspace. The write operation requires an SPI write, then
> toggling of a GPIO, so the lock aims to protect the sanity of the entire
> sequence of operation.
> 
> 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>

Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> ---
>  drivers/iio/dac/ti-dac7612.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/dac/ti-dac7612.c b/drivers/iio/dac/ti-dac7612.c
> index 07c9f39d54f1..4c0f4b5e9ff4 100644
> --- a/drivers/iio/dac/ti-dac7612.c
> +++ b/drivers/iio/dac/ti-dac7612.c
> @@ -22,6 +22,14 @@ struct dac7612 {
>  	struct gpio_desc *loaddacs;
>  	uint16_t cache[2];
>  
> +	/*
> +	 * Lock to protect the state of the device from potential concurrent
> +	 * write accesses from userspace. The write operation requires an
> +	 * SPI write, then toggling of a GPIO, so the lock aims to protect
> +	 * the sanity of the entire sequence of operation.
> +	 */
> +	struct mutex lock;
> +
>  	/*
>  	 * DMA (thus cache coherency maintenance) requires the
>  	 * transfer buffers to live in their own cache lines.
> @@ -101,9 +109,9 @@ static int dac7612_write_raw(struct iio_dev *iio_dev,
>  	if (val == priv->cache[chan->channel])
>  		return 0;
>  
> -	mutex_lock(&iio_dev->mlock);
> +	mutex_lock(&priv->lock);
>  	ret = dac7612_cmd_single(priv, chan->channel, val);
> -	mutex_unlock(&iio_dev->mlock);
> +	mutex_unlock(&priv->lock);
>  
>  	return ret;
>  }
> @@ -145,6 +153,8 @@ static int dac7612_probe(struct spi_device *spi)
>  	iio_dev->num_channels = ARRAY_SIZE(priv->cache);
>  	iio_dev->name = spi_get_device_id(spi)->name;
>  
> +	mutex_init(&priv->lock);
> +
>  	for (i = 0; i < ARRAY_SIZE(priv->cache); i++) {
>  		ret = dac7612_cmd_single(priv, i, 0);
>  		if (ret)