staging: comedi: das16 introduce das16_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/das16.c

@@ -993,6 +993,41 @@ static void das16_reset(struct comedi_device *dev)
 	outb(0, dev->iobase + DAS16_TIMER_BASE_REG + i8254_control_reg);
 }
 
+static int das16_alloc_dma(struct comedi_device *dev, unsigned int dma_chan)
+{
+	struct das16_private_struct *devpriv = dev->private;
+	struct das16_dma_desc *dma;
+	unsigned long flags;
+	int i;
+
+	if (!(dma_chan == 1 || dma_chan == 3))
+		return 0;
+
+	if (request_dma(dma_chan, dev->board_name))
+		return 0;
+	devpriv->dma_chan = dma_chan;
+
+	for (i = 0; i < 2; i++) {
+		dma = &devpriv->dma_desc[i];
+
+		dma->virt_addr = pci_alloc_consistent(NULL, DAS16_DMA_SIZE,
+						      &dma->hw_addr);
+		if (!dma->virt_addr)
+			return -ENOMEM;
+	}
+
+	flags = claim_dma_lock();
+	disable_dma(devpriv->dma_chan);
+	set_dma_mode(devpriv->dma_chan, DMA_MODE_READ);
+	release_dma_lock(flags);
+
+	init_timer(&devpriv->timer);
+	devpriv->timer.function = das16_timer_interrupt;
+	devpriv->timer.data = (unsigned long)dev;
+
+	return 0;
+}
+
 static int das16_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 {
 	const struct das16_board *board = dev->board_ptr;
@@ -1000,7 +1035,6 @@ static int das16_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	struct comedi_subdevice *s;
 	struct comedi_lrange *lrange;
 	struct comedi_krange *krange;
-	unsigned int dma_chan = it->options[2];
 	unsigned int status;
 	int ret;
 
@@ -1055,39 +1089,9 @@ static int das16_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 			devpriv->clockbase = I8254_OSC_BASE_1MHZ;
 	}
 
-	/* initialize dma */
-	if (dma_chan == 1 || dma_chan == 3) {
-		unsigned long flags;
-		int i;
-
-		if (request_dma(dma_chan, dev->board_name)) {
-			dev_err(dev->class_dev,
-				"failed to request dma channel %i\n",
-				dma_chan);
-			return -EINVAL;
-		}
-		devpriv->dma_chan = dma_chan;
-
-		/* allocate dma buffers */
-		for (i = 0; i < 2; i++) {
-			struct das16_dma_desc *dma = &devpriv->dma_desc[i];
-
-			dma->virt_addr = pci_alloc_consistent(NULL,
-							      DAS16_DMA_SIZE,
-							      &dma->hw_addr);
-			if (!dma->virt_addr)
-				return -ENOMEM;
-		}
-
-		flags = claim_dma_lock();
-		disable_dma(devpriv->dma_chan);
-		set_dma_mode(devpriv->dma_chan, DMA_MODE_READ);
-		release_dma_lock(flags);
-
-		init_timer(&devpriv->timer);
-		devpriv->timer.function = das16_timer_interrupt;
-		devpriv->timer.data = (unsigned long)dev;
-	}
+	ret = das16_alloc_dma(dev, it->options[2]);
+	if (ret)
+		return ret;
 
 	/* get any user-defined input range */
 	if (board->ai_pg == das16_pg_none &&