staging: comedi: pcl812: introduce pcl812_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/pcl812.c

@@ -1192,6 +1192,34 @@ static void pcl812_set_ai_range_table(struct comedi_device *dev,
 	}
 }
 
+static int pcl812_alloc_dma(struct comedi_device *dev, unsigned int dma_chan)
+{
+	struct pcl812_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 = 1;	/* we want 8KB */
+	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 pcl812_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 {
 	const struct pcl812_board *board = dev->board_ptr;
@@ -1200,7 +1228,6 @@ static int pcl812_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	int n_subdevices;
 	int subdev;
 	int ret;
-	int i;
 
 	devpriv = comedi_alloc_devpriv(dev, sizeof(*devpriv));
 	if (!devpriv)
@@ -1218,30 +1245,10 @@ static int pcl812_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	}
 
 	/* 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 = 1;	/* we want 8KB */
-		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 = pcl812_alloc_dma(dev, it->options[2]);
+		if (ret)
+			return ret;
 	}
 
 	/* differential analog inputs? */