Re: [PATCH AUTOSEL 5.4 117/350] iio: dac: ad7303: replace mlock with own lock

[Jonathan Cameron <jic23@jic23.retrosnub.co.uk>]

On Tue, 10 Dec 2019 16:03:42 -0500
Sasha Levin <sashal@kernel.org> wrote:

> From: Alexandru Ardelean <alexandru.ardelean@analog.com>
> 
> [ Upstream commit c991bf9b650f39481cf3c1137092d4754a2c75de ]
> 
> This change replaces indio_dev's mlock with the driver's own lock. The lock
> is mostly needed to protect state when changing the `dac_cache` info.
> The lock has been extended to `ad7303_read_raw()`, to make sure that the
> cache is updated if an SPI-write is already in progress.
This is not a fix.  It's undoing some slightly nasty layer violations
that we are trying to drive out of IIO, but as far as I know there
is no actual bug with what was there before.

I won't do any harm though other than adding noise.

Jonathan

> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  drivers/iio/dac/ad7303.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/dac/ad7303.c b/drivers/iio/dac/ad7303.c
> index 8de9f40226e62..14bbac6bee982 100644
> --- a/drivers/iio/dac/ad7303.c
> +++ b/drivers/iio/dac/ad7303.c
> @@ -41,6 +41,7 @@ struct ad7303_state {
>  	struct regulator *vdd_reg;
>  	struct regulator *vref_reg;
>  
> +	struct mutex lock;
>  	/*
>  	 * DMA (thus cache coherency maintenance) requires the
>  	 * transfer buffers to live in their own cache lines.
> @@ -79,7 +80,7 @@ static ssize_t ad7303_write_dac_powerdown(struct iio_dev *indio_dev,
>  	if (ret)
>  		return ret;
>  
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&st->lock);
>  
>  	if (pwr_down)
>  		st->config |= AD7303_CFG_POWER_DOWN(chan->channel);
> @@ -90,7 +91,7 @@ static ssize_t ad7303_write_dac_powerdown(struct iio_dev *indio_dev,
>  	 * mode, so just write one of the DAC channels again */
>  	ad7303_write(st, chan->channel, st->dac_cache[chan->channel]);
>  
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->lock);
>  	return len;
>  }
>  
> @@ -116,7 +117,9 @@ static int ad7303_read_raw(struct iio_dev *indio_dev,
>  
>  	switch (info) {
>  	case IIO_CHAN_INFO_RAW:
> +		mutex_lock(&st->lock);
>  		*val = st->dac_cache[chan->channel];
> +		mutex_unlock(&st->lock);
>  		return IIO_VAL_INT;
>  	case IIO_CHAN_INFO_SCALE:
>  		vref_uv = ad7303_get_vref(st, chan);
> @@ -144,11 +147,11 @@ static int ad7303_write_raw(struct iio_dev *indio_dev,
>  		if (val >= (1 << chan->scan_type.realbits) || val < 0)
>  			return -EINVAL;
>  
> -		mutex_lock(&indio_dev->mlock);
> +		mutex_lock(&st->lock);
>  		ret = ad7303_write(st, chan->address, val);
>  		if (ret == 0)
>  			st->dac_cache[chan->channel] = val;
> -		mutex_unlock(&indio_dev->mlock);
> +		mutex_unlock(&st->lock);
>  		break;
>  	default:
>  		ret = -EINVAL;
> @@ -211,6 +214,8 @@ static int ad7303_probe(struct spi_device *spi)
>  
>  	st->spi = spi;
>  
> +	mutex_init(&st->lock);
> +
>  	st->vdd_reg = devm_regulator_get(&spi->dev, "Vdd");
>  	if (IS_ERR(st->vdd_reg))
>  		return PTR_ERR(st->vdd_reg);