staging: comedi: das1800: fix possible NULL dereference

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 in das1800_ai_cancel() and tidy up the comments to fix the
checkpatch.pl issues:
WARNING: line over 80 characters

It's probably harmless in das1800_ai_setup_dma() because the 'desc' pointer
will not be used if DMA is disabled but fix it there also.

Fixes: 99dfc3357e98 ("staging: comedi: das1800: remove depends on ISA_DMA_API limitation")
Cc: <stable@vger.kernel.org> # 4.0+
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/das1800.c b/drivers/staging/comedi/drivers/das1800.c
index 940781183fac4e450503c7b3cd5df6c30bde6d0c..3be10963f98b6bd2296ee1972118fbd562091738 100644 (file)
--- a/drivers/staging/comedi/drivers/das1800.c
+++ b/drivers/staging/comedi/drivers/das1800.c
@@ -567,14 +567,17 @@ static int das1800_cancel(struct comedi_device *dev, struct comedi_subdevice *s)
        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;
@@ -934,13 +937,14 @@ static void das1800_ai_setup_dma(struct comedi_device *dev,
 {
        struct das1800_private *devpriv = dev->private;
        struct comedi_isadma *dma = devpriv->dma;
-       struct comedi_isadma_desc *desc = &dma->desc[0];
+       struct comedi_isadma_desc *desc;
        unsigned int bytes;
 
        if ((devpriv->irq_dma_bits & DMA_ENABLED) == 0)
                return;
 
        dma->cur_dma = 0;
+       desc = &dma->desc[0];
 
        /* determine a dma transfer size to fill buffer in 0.3 sec */
        bytes = das1800_ai_transfer_size(dev, s, desc->maxsize, 300000000);