staging: comedi: pcl818: introduce pcl818_alloc_dma()

DMA is optional with this driver. Introduce a helper function to request
the DMA channel and allocate the buffers. Don't fail the driver attach
if the user passed an invalid DMA channel or the channel cannot be
requested.
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>

drivers/staging/comedi/drivers/pcl818.c

@@ -1054,13 +1054,40 @@ static void pcl818_set_ai_range_table(struct comedi_device *dev,
 	}
 }
 
+static int pcl818_alloc_dma(struct comedi_device *dev, unsigned int dma_chan)
+{
+	struct pcl818_private *devpriv = dev->private;
+	int i;
+
+	if (!(dma_chan == 3 || dma_chan == 1))
+		return 0;
+
+	if (request_dma(dma_chan, dev->board_name))
+		return 0;
+	devpriv->dma = dma_chan;
+
+	devpriv->dmapages = 2;	/* we need 16KB */
+	devpriv->hwdmasize = (1 << devpriv->dmapages) * PAGE_SIZE;
+
+	for (i = 0; i < 2; i++) {
+		unsigned long dmabuf;
+
+		dmabuf = __get_dma_pages(GFP_KERNEL, devpriv->dmapages);
+		if (!dmabuf)
+			return -ENOMEM;
+
+		devpriv->dmabuf[i] = dmabuf;
+		devpriv->hwdmaptr[i] = virt_to_bus((void *)dmabuf);
+	}
+	return 0;
+}
+
 static int pcl818_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 {
 	const struct pcl818_board *board = dev->board_ptr;
 	struct pcl818_private *devpriv;
 	struct comedi_subdevice *s;
 	int ret;
-	int i;
 
 	devpriv = comedi_alloc_devpriv(dev, sizeof(*devpriv));
 	if (!devpriv)
@@ -1084,30 +1111,10 @@ static int pcl818_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 		devpriv->usefifo = 1;
 
 	/* we need an IRQ to do DMA on channel 3 or 1 */
-	if (dev->irq && board->has_dma &&
-	    (it->options[2] == 3 || it->options[2] == 1)) {
-		ret = request_dma(it->options[2], dev->board_name);
-		if (ret) {
-			dev_err(dev->class_dev,
-				"unable to request DMA channel %d\n",
-				it->options[2]);
-			return -EBUSY;
-		}
-		devpriv->dma = it->options[2];
-
-		devpriv->dmapages = 2;	/* we need 16KB */
-		devpriv->hwdmasize = (1 << devpriv->dmapages) * PAGE_SIZE;
-
-		for (i = 0; i < 2; i++) {
-			unsigned long dmabuf;
-
-			dmabuf = __get_dma_pages(GFP_KERNEL, devpriv->dmapages);
-			if (!dmabuf)
-				return -ENOMEM;
-
-			devpriv->dmabuf[i] = dmabuf;
-			devpriv->hwdmaptr[i] = virt_to_bus((void *)dmabuf);
-		}
+	if (dev->irq && board->has_dma) {
+		ret = pcl818_alloc_dma(dev, it->options[2]);
+		if (ret)
+			return ret;
 	}
 
 	ret = comedi_alloc_subdevices(dev, 4);