patch "staging: comedi: ni_mio_common: fix AO inttrig backwards" added to staging-linus

This is a note to let you know that I've just added the patch titled

staging: comedi: ni_mio_common: fix AO inttrig backwards

to my staging git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Ian Abbott <[email protected]>
Date: Tue, 19 Jul 2016 12:17:39 +0100
Subject: staging: comedi: ni_mio_common: fix AO inttrig backwards
compatibility

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.

---
 drivers/staging/comedi/drivers/ni_mio_common.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

index 3cf3c05c5ef2..0f97d7b611d7 100644
@@ -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;
 
 	/*

2.9.3