staging: comedi: ni_mio_common: fix AO inttrig backwards compatibility
Commit ebb657ba ("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@mev.co.uk> Reported-by: Spencer Olson <olsonse@umich.edu> Fixes: ebb657ba ("staging: comedi: ni_mio_common: clarify the cmd->start_arg validation and use") Cc: stable <stable@vger.kernel.org> Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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