staging: comedi: ni_mio_common: fix AO inttrig backwards compatibility

commit f0f4b0cc3a8cffd983f5940d46cd0227f3f5710a upstream.

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@mev.co.uk>
Reported-by: Spencer Olson <olsonse@umich.edu>
Fixes: ebb657babfa9 ("staging: comedi: ni_mio_common: clarify the cmd->start_arg validation and use")
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/ni_mio_common.c b/drivers/staging/comedi/drivers/ni_mio_common.c
index 27fbf1a810975e86faa7819f06ff717ae842d957..955f802a1d0a6c93dd3e4bf9fe523d8f78f64c3d 100644 (file)
--- a/drivers/staging/comedi/drivers/ni_mio_common.c
+++ b/drivers/staging/comedi/drivers/ni_mio_common.c
@@ -2823,7 +2823,15 @@ 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;
 
        /* Null trig at beginning prevent ao start trigger from executing more than