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

[<gregkh@linuxfoundation.org>]

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 f0f4b0cc3a8cffd983f5940d46cd0227f3f5710a Mon Sep 17 00:00:00 2001
From: Ian Abbott <abbotti@mev.co.uk>
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.

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")
Cc: stable <stable@vger.kernel.org>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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 3cf3c05c5ef2..0f97d7b611d7 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;
 
 	/*
-- 
2.9.3