On Wed, 17 Jun 2020 21:29:27 -0400
Sasha Levin <sashal@xxxxxxxxxx> wrote:
> From: Lars-Peter Clausen <lars@xxxxxxxxxx>
>
> [ Upstream commit b7329249ea5b08b2a1c2c3f24a2f4c495c4f14b8 ]
>
> Before activating a buffer make sure that at least one channel is enabled.
> Activating a buffer with 0 channels enabled doesn't make too much sense and
> disallowing this case makes sure that individual driver don't have to add
> special case code to handle it.
>
> Currently, without this patch enabling a buffer is possible and no error is
> produced. With this patch -EINVAL is returned.
>
> An example of execution with this patch and some instrumented print-code:
> root@analog:~# cd /sys/bus/iio/devices/iio\:device3/buffer
> root@analog:/sys/bus/iio/devices/iio:device3/buffer# echo 1 > enable
> 0: iio_verify_update 748 indio_dev->masklength 2 *insert_buffer->scan_mask 00000000
> 1: iio_verify_update 753
> 2:__iio_update_buffers 1115 ret -22
> 3: iio_buffer_store_enable 1241 ret -22
> -bash: echo: write error: Invalid argument
> 1, 2 & 3 are exit-error paths. 0 the first print in iio_verify_update()
> rergardless of error path.
>
> Without this patch (and same instrumented print-code):
> root@analog:~# cd /sys/bus/iio/devices/iio\:device3/buffer
> root@analog:/sys/bus/iio/devices/iio:device3/buffer# echo 1 > enable
> 0: iio_verify_update 748 indio_dev->masklength 2 *insert_buffer->scan_mask 00000000
> root@analog:/sys/bus/iio/devices/iio:device3/buffer#
> Buffer is enabled with no error.
>
> Note from Jonathan: Probably not suitable for automatic application to stable.
> This has been there from the very start. It tidies up an odd corner
> case but won't effect any 'real' users.
>
As noted. I don't think it matters if we do apply this to stable.
It closes an interface oddity rather than an actual known bug.
> Fixes: 84b36ce5f79c0 ("staging:iio: Add support for multiple buffers")
> Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
> drivers/iio/industrialio-buffer.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 864a61b05665..fea41b328ab9 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -641,6 +641,13 @@ static int iio_verify_update(struct iio_dev *indio_dev,
> bool scan_timestamp;
> unsigned int modes;
>
> + if (insert_buffer &&
> + bitmap_empty(insert_buffer->scan_mask, indio_dev->masklength)) {
> + dev_dbg(&indio_dev->dev,
> + "At least one scan element must be enabled first\n");
> + return -EINVAL;
> + }
> +
> memset(config, 0, sizeof(*config));
>
> /*
