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 <abbo...@mev.co.uk>
> Reported-by: Spencer Olson <olso...@umich.edu>
> 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;
But, either way:
Reviewed-by: H Hartley Sweeten <hswee...@visionengravers.com>
Thanks!
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