[PATCH 28/35] staging: comedi: das1800: fix das1800_ai_cancel()

[H Hartley Sweeten]

DMA is optional with this driver. If it was not enabled the devpriv->dma
pointer will be NULL. Fix the possible NULL pointer dereference when trying
to disable the DMA channels.

Also, tidy up the comments to fix the checkpatch.pl issues:
WARNING: line over 80 characters

Signed-off-by: H Hartley Sweeten <hsweeten at visionengravers.com>
Cc: Ian Abbott <abbotti at mev.co.uk>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 drivers/staging/comedi/drivers/das1800.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/staging/comedi/drivers/das1800.c b/drivers/staging/comedi/drivers/das1800.c
index bdf30f8..d8f4e3f 100644
--- a/drivers/staging/comedi/drivers/das1800.c
+++ b/drivers/staging/comedi/drivers/das1800.c
@@ -458,14 +458,17 @@ static int das1800_ai_cancel(struct comedi_device *dev,
 	struct comedi_isadma_desc *desc;
 	int i;
 
-	outb(0x0, dev->iobase + DAS1800_STATUS);	/* disable conversions */
-	outb(0x0, dev->iobase + DAS1800_CONTROL_B);	/* disable interrupts and dma */
-	outb(0x0, dev->iobase + DAS1800_CONTROL_A);	/* disable and clear fifo and stop triggering */
-
-	for (i = 0; i < 2; i++) {
-		desc = &dma->desc[i];
-		if (desc->chan)
-			comedi_isadma_disable(desc->chan);
+	/* disable and stop conversions */
+	outb(0x0, dev->iobase + DAS1800_STATUS);
+	outb(0x0, dev->iobase + DAS1800_CONTROL_B);
+	outb(0x0, dev->iobase + DAS1800_CONTROL_A);
+
+	if (dma) {
+		for (i = 0; i < 2; i++) {
+			desc = &dma->desc[i];
+			if (desc->chan)
+				comedi_isadma_disable(desc->chan);
+		}
 	}
 
 	return 0;
-- 
2.6.3