Re: [PATCH v2] iio: buffer: Don't allow buffers without any channels enabled to be activated

[Ardelean, Alexandru]

On Wed, 2020-03-25 at 17:57 +0200, Andy Shevchenko wrote:
> [External]
> 
> On Wed, Mar 25, 2020 at 12:02 PM Alexandru Ardelean
> <alexandru.ardelean@xxxxxxxxxx> wrote:
> > From: Lars-Peter Clausen <lars@xxxxxxxxxx>
> > 
> > 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.
> > 
> > Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
> > ---
> > 
> > Changelog v1 -> v2:
> > * moved check in iio_verify_update()
> > * added dev_dbg() message; should help some folks understand the message
> > * documented steps to reproduce
> > * added Fixes tag; hopefully the tag is the good one; if needed, it can be
> >   dropped; this has been around for ~8 years; no idea if it's worth
> >   backporting
> 
> Where?

stable/fixes/lts-kernels
don't have a really good clue about where these things need backporting;

> 
> >  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 5ff34ce8b6a2..e6fa1a4e135d 100644
> > --- a/drivers/iio/industrialio-buffer.c
> > +++ b/drivers/iio/industrialio-buffer.c
> > @@ -686,6 +686,13 @@ 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));
> >         config->watermark = ~0;
> > 
> > --
> > 2.17.1
> > 
> 
>