[ 3.5.y.z extended stable ] Patch "staging: comedi: ni_labpc: correct differential channel" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    staging: comedi: ni_labpc: correct differential channel

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 6b0b135e6614cf025d468996d268ba0afc7874c4 Mon Sep 17 00:00:00 2001
From: Ian Abbott <abbotti at mev.co.uk>
Date: Wed, 27 Feb 2013 12:52:45 +0000
Subject: [PATCH] staging: comedi: ni_labpc: correct differential channel
 sequence for AI commands

Commit 4c4bc25d0fa6beaf054c0b4c3b324487f266c820 upstream.

Tuomas <tvainikk _at_ gmail _dot_ com> reported problems getting
meaningful output from a Lab-PC+ in differential mode for AI cmds, but
AI insn reads gave correct readings.  He tracked it down to two
problems, one of which is addressed by this patch.

It seems the setting of the channel bits for particular scanning modes
was incorrect for differential mode.  (Only half the number of channels
are available in differential mode; comedi refers to them as channels 0,
1, 2 and 3, but the hardware documentation refers to them as channels 0,
2, 4 and 6.)  In differential mode, the setting of the channel enable
bits in the command1 register should depend on whether the scan enable
bit is set.  Effectively, we need to double the comedi channel number
when the scan enable bit is not set in differential mode.  The scan
enable bit gets set when the AI scan mode is `MODE_MULT_CHAN_UP` or
`MODE_MULT_CHAN_DOWN`, and gets cleared when the AI scan mode is
`MODE_SINGLE_CHAN` or `MODE_SINGLE_CHAN_INTERVAL`.  The existing test
for whether the comedi channel number needs to be doubled in
differential mode is incorrect in `labpc_ai_cmd()`.  This patch corrects
the test.

Thanks to Tuomas for suggesting the fix.

Signed-off-by: Ian Abbott <abbotti at mev.co.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/staging/comedi/drivers/ni_labpc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/drivers/ni_labpc.c b/drivers/staging/comedi/drivers/ni_labpc.c
index 5b2b966..1e472ba 100644
--- a/drivers/staging/comedi/drivers/ni_labpc.c
+++ b/drivers/staging/comedi/drivers/ni_labpc.c
@@ -1259,7 +1259,9 @@ static int labpc_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s)
 	else
 		channel = CR_CHAN(cmd->chanlist[0]);
 	/* munge channel bits for differential / scan disabled mode */
-	if (labpc_ai_scan_mode(cmd) != MODE_SINGLE_CHAN && aref == AREF_DIFF)
+	if ((labpc_ai_scan_mode(cmd) == MODE_SINGLE_CHAN ||
+	     labpc_ai_scan_mode(cmd) == MODE_SINGLE_CHAN_INTERVAL) &&
+	    aref == AREF_DIFF)
 		channel *= 2;
 	devpriv->command1_bits |= ADC_CHAN_BITS(channel);
 	devpriv->command1_bits |= thisboard->ai_range_code[range];
--
1.8.1.2