Re: [PATCH 14/15] iio: health: max30102: do not use internal iio_dev lock

Jonathan Cameron
2022-09-24T15:54:50Z

On Tue, 20 Sep 2022 13:28:20 +0200
Nuno Sá <nuno.sa@analog.com> wrote:

> The pattern used in this device does not quite fit in the
> iio_device_claim_direct_mode() typical usage. In this case,
> iio_buffer_enabled() was being used not to prevent the raw access
> but to decide whether or not the device needs to be powered on before.
> If buffering, then the device is already on. To guarantee the same
> behavior, a combination of locks is being used:
>
> 1. Use iio_device_claim_direct_mode() to check if direct mode can be
> claimed and if we can, then we keep it until the reading is done (which
> also means the device will be powered on and off);
> 2. If already buffering, we need to make sure that buffering is not
> disabled (and hence, powering off the device) while doing a raw read. For
> that, we can make use of the local lock that already exists.
>
> Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Obviously same dance in here as the related previous patch. So same solution
needs adopting. I just thought I'd reply to make sure we didn't forget to
cover them both :)

Jonathan

> ---
> drivers/iio/health/max30102.c | 25 +++++++++++++++++++------
> 1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/iio/health/max30102.c b/drivers/iio/health/max30102.c
> index abbcef563807..e984c78b99f6 100644
> --- a/drivers/iio/health/max30102.c
> +++ b/drivers/iio/health/max30102.c
> @@ -227,9 +227,20 @@ static int max30102_buffer_postenable(struct iio_dev *indio_dev)
> static int max30102_buffer_predisable(struct iio_dev *indio_dev)
> {
> struct max30102_data *data = iio_priv(indio_dev);
> + int ret;
> +
> + /*
> + * As stated in the comment in the read_raw() function, temperature
> + * can only be acquired if the engine is running. As such the mutex
> + * is used to make sure we do not power down while doing a temperature
> + * reading.
> + */
> + mutex_lock(&data->lock);
> + ret = max30102_set_powermode(data, MAX30102_REG_MODE_CONFIG_MODE_NONE,
> + false);
> + mutex_unlock(&data->lock);
>
> - return max30102_set_powermode(data, MAX30102_REG_MODE_CONFIG_MODE_NONE,
> - false);
> + return ret;
> }
>
> static const struct iio_buffer_setup_ops max30102_buffer_setup_ops = {
> @@ -477,12 +488,14 @@ static int max30102_read_raw(struct iio_dev *indio_dev,
> * Temperature reading can only be acquired when not in
> * shutdown; leave shutdown briefly when buffer not running
> */
> - mutex_lock(&indio_dev->mlock);
> - if (!iio_buffer_enabled(indio_dev))
> + if (!iio_device_claim_direct_mode(indio_dev)) {
> ret = max30102_get_temp(data, val, true);
> - else
> + iio_device_release_direct_mode(indio_dev);
> + } else {
> + mutex_lock(&data->lock);
> ret = max30102_get_temp(data, val, false);
> - mutex_unlock(&indio_dev->mlock);
> + mutex_unlock(&data->lock);
> + }
> if (ret)
> return ret;