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SubjectRe: [PATCH 5/5] iio: adc: rockchip_saradc: Replace indio_dev->mlock with own device lock
On Mon, 28 Sep 2020 16:13:33 +0300
Mircea Caprioru <mircea.caprioru@analog.com> wrote:

> From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
>
> As part of the general cleanup of indio_dev->mlock, this change replaces
> it with a local lock on the device's state structure.
>
> This is part of a bigger cleanup.
> Link: https://lore.kernel.org/linux-iio/CA+U=Dsoo6YABe5ODLp+eFNPGFDjk5ZeQEceGkqjxXcVEhLWubw@mail.gmail.com/
>
> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> Signed-off-by: Mircea Caprioru <mircea.caprioru@analog.com>

Another driver with buffered support which means we need to think
harder about what is going on with these locks.

> ---
> drivers/iio/adc/rockchip_saradc.c | 21 ++++++++++++++++-----
> 1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/iio/adc/rockchip_saradc.c b/drivers/iio/adc/rockchip_saradc.c
> index 1f3d7d639d37..80084c526cc6 100644
> --- a/drivers/iio/adc/rockchip_saradc.c
> +++ b/drivers/iio/adc/rockchip_saradc.c
> @@ -53,6 +53,15 @@ struct rockchip_saradc {
> const struct rockchip_saradc_data *data;
> u16 last_val;
> const struct iio_chan_spec *last_chan;
> + /*
> + * Lock to protect the device state during a potential concurrent
> + * read access from userspace. Reading a raw value requires a sequence
> + * of register writes, then a wait for a completion callback,
> + * and finally a register read, during which userspace could issue
> + * another read request. This lock protects a read access from
> + * ocurring before another one has finished.
> + */
> + struct mutex lock;
> };
>
> static void rockchip_saradc_power_down(struct rockchip_saradc *info)
> @@ -92,17 +101,17 @@ static int rockchip_saradc_read_raw(struct iio_dev *indio_dev,
>
> switch (mask) {
> case IIO_CHAN_INFO_RAW:
> - mutex_lock(&indio_dev->mlock);
> + mutex_lock(&info->lock);

Probably a case for iio_device_claim_direct_mode() as I doubt we want
to enter buffered mode when halfway through this.


>
> ret = rockchip_saradc_conversion(info, chan);
> if (ret) {
> rockchip_saradc_power_down(info);
> - mutex_unlock(&indio_dev->mlock);
> + mutex_unlock(&info->lock);
> return ret;
> }
>
> *val = info->last_val;
> - mutex_unlock(&indio_dev->mlock);
> + mutex_unlock(&info->lock);
> return IIO_VAL_INT;
> case IIO_CHAN_INFO_SCALE:
> ret = regulator_get_voltage(info->vref);
> @@ -254,7 +263,7 @@ static irqreturn_t rockchip_saradc_trigger_handler(int irq, void *p)
> int ret;
> int i, j = 0;
>
> - mutex_lock(&i_dev->mlock);
> + mutex_lock(&info->lock);
Hmm. I wonder what this was meant to protect?

I can't see why we need it if we are claiming direct mode correctly above.

>
> for_each_set_bit(i, i_dev->active_scan_mask, i_dev->masklength) {
> const struct iio_chan_spec *chan = &i_dev->channels[i];
> @@ -271,7 +280,7 @@ static irqreturn_t rockchip_saradc_trigger_handler(int irq, void *p)
>
> iio_push_to_buffers_with_timestamp(i_dev, &data, iio_get_time_ns(i_dev));
> out:
> - mutex_unlock(&i_dev->mlock);
> + mutex_unlock(&info->lock);
>
> iio_trigger_notify_done(i_dev->trig);
>
> @@ -332,6 +341,8 @@ static int rockchip_saradc_probe(struct platform_device *pdev)
> info->reset = NULL;
> }
>
> + mutex_init(&info->lock);
> +
> init_completion(&info->completion);
>
> irq = platform_get_irq(pdev, 0);

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