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

Jonathan Cameron
2019-12-15T15:55:12Z

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);