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

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