Re: [PATCH AUTOSEL 4.4 23/60] iio: buffer: Don't allow buffers without any channels enabled to be activated

[Sasha Levin]

On Fri, Jun 19, 2020 at 05:27:33PM +0100, Jonathan Cameron wrote:
> 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.

I'll drop it, thanks!

--
Thanks,
Sasha