Re: [PATCH 1/5] iio:magnetometer:mag3110: Report busy in _read_raw() / write_raw() when buffer is enabled

[Jonathan Cameron <jic23@kernel.org>]

On 10/01/14 21:59, Peter Meerwald wrote:
> individual reads are not permitted concurrently with buffered reads
>
This isn't technically a requirement.  The reasoning behind doing it
is normally that a userspace read could mess up the timing of a fixed
frequency triggered signal.  I guess that's true here but is probably
not a strong enough reason to make an ABI change.

Perhaps an ammended description to describe the reasoning for not
allowing it in this driver?

While obscure this is an ABI change as reads that would previously
have succeeded will fail (I doubt anyone will notice, but you never
know...)

The arguement for protecting against changes in the sampling frequency
is perhaps a little stronger as that may cause nasty issues in the buffered
read...
> Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
> ---
>   drivers/iio/magnetometer/mag3110.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/drivers/iio/magnetometer/mag3110.c b/drivers/iio/magnetometer/mag3110.c
> index 4b65b6d..b88cb44 100644
> --- a/drivers/iio/magnetometer/mag3110.c
> +++ b/drivers/iio/magnetometer/mag3110.c
> @@ -154,6 +154,9 @@ static int mag3110_read_raw(struct iio_dev *indio_dev,
>
>   	switch (mask) {
>   	case IIO_CHAN_INFO_RAW:
> +		if (iio_buffer_enabled(indio_dev))
> +			return -EBUSY;
> +
>   		switch (chan->type) {
>   		case IIO_MAGN: /* in 0.1 uT / LSB */
>   			ret = mag3110_read(data, buffer);
> @@ -199,6 +202,9 @@ static int mag3110_write_raw(struct iio_dev *indio_dev,
>   	struct mag3110_data *data = iio_priv(indio_dev);
>   	int rate;
>
> +	if (iio_buffer_enabled(indio_dev))
> +		return -EBUSY;
> +
>   	switch (mask) {
>   	case IIO_CHAN_INFO_SAMP_FREQ:
>   		rate = mag3110_get_samp_freq_index(data, val, val2);
>