Re: [PATCH] staging: comedi: ni_mio_common: fix AO inttrig backwards compatibility

[Ian Abbott]

On 20/07/16 16:55, Hartley Sweeten wrote:
> On Tuesday, July 19, 2016 4:18 AM, Ian Abbott wrote:
> > Commit ebb657babfa9 ("staging: comedi: ni_mio_common: clarify the
> > cmd->start_arg validation and use") introduced a backwards compatibility
> > issue in the use of asynchronous commands on the AO subdevice when
> > `start_src` is `TRIG_EXT`.  Valid values for `start_src` are `TRIG_INT`
> > (for internal, software trigger), and `TRIG_EXT` (for external trigger).
> > When set to `TRIG_EXT`.  In both cases, the driver relies on an
> > internal, software trigger to set things up (allowing the user
> > application to write sufficient samples to the data buffer before the
> > trigger), so it acts as a software "pre-trigger" in the `TRIG_EXT` case.
> > The software trigger is handled by `ni_ao_inttrig()`.
> >
> > Prior to the above change, when `start_src` was `TRIG_INT`, `start_arg`
> > was required to be 0, and `ni_ao_inttrig()` checked that the software
> > trigger number was also 0.  After the above change, when `start_src` was
> > `TRIG_INT`, any value was allowed for `start_arg`, and `ni_ao_inttrig()`
> > checked that the software trigger number matched this `start_arg` value.
> > The backwards compatibility issue is that the internal trigger number
> > now has to match `start_arg` when `start_src` is `TRIG_EXT` when it
> > previously had to be 0.
> >
> > Fix the backwards compatibility issue in `ni_ao_inttrig()` by always
> > allowing software trigger number 0 when `start_src` is something other
> > than `TRIG_INT`.
> >
> > Thanks to Spencer Olson for reporting the issue.
> >
> > Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
> > Reported-by: Spencer Olson <olsonse@xxxxxxxxx>
> > Fixes: ebb657babfa9 ("staging: comedi: ni_mio_common: clarify the
> >   cmd->start_arg validation and use")
> > ---
> >  drivers/staging/comedi/drivers/ni_mio_common.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/comedi/drivers/ni_mio_common.c b/drivers/staging/comedi/drivers/ni_mio_common.c
> > index 8dabb19..9f4036f 100644
> > --- a/drivers/staging/comedi/drivers/ni_mio_common.c
> > +++ b/drivers/staging/comedi/drivers/ni_mio_common.c
> > @@ -2772,7 +2772,15 @@ static int ni_ao_inttrig(struct comedi_device *dev,
> >  	int i;
> >  	static const int timeout = 1000;
> >
> > -	if (trig_num != cmd->start_arg)
> > +	/*
> > +	 * Require trig_num == cmd->start_arg when cmd->start_src == TRIG_INT.
> > +	 * For backwards compatibility, also allow trig_num == 0 when
> > +	 * cmd->start_src != TRIG_INT (i.e. when cmd->start_src == TRIG_EXT);
> > +	 * in that case, the internal trigger is being used as a pre-trigger
> > +	 * before the external trigger.
> > +	 */
> > +	if (!(trig_num == cmd->start_arg ||
> > +	      (trig_num == 0 && cmd->start_src != TRIG_INT)))
> >  		return -EINVAL;
>
> Ian,
>
> I think this test is a bit clearer:
>
> +	/*
> +	 * Require trig_num == cmd->start_arg when cmd->start_src == TRIG_INT.
> +	 * For backwards compatibility, any trig_num is valid when
> +	 * cmd->start_src != TRIG_INT (i.e. when cmd->start_src == TRIG_EXT);
> +	 * in that case, the internal trigger is being used as a pre-trigger
> +	 * before the external trigger.
> +	 */
> +	if (cmd->start_src == TRIG_INT && trig_num != cmd->start_arg)
> 		return -EINVAL;

True, but I restricted it to only accept trig_num values that have been 
valid in the past.

> But, either way:
>
> Reviewed-by: H Hartley Sweeten <hsweeten@xxxxxxxxxxxxxxxxxxx>
>
> Thanks!

Thanks for the review.

--
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@xxxxxxxxx> )=-
-=(                          Web: http://www.mev.co.uk/  )=-