staging: comedi: pcl816: introduce pcl816_alloc_dma()

The IRA and DMA are optional with this driver but both are required to
support async commands. Introduce a helper function to request the IRQ
and DMA channel and allocate the buffers. Don't fail the driver attach
if the user passed an invalid IRQ or DMA channel or they 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/pcl816.c

@@ -657,13 +657,59 @@ static void pcl816_reset(struct comedi_device *dev)
 	outb(0, dev->iobase + PCL816_DO_DI_MSB_REG);
 }
 
+static int pcl816_alloc_dma(struct comedi_device *dev,
+			    unsigned int irq_num, unsigned int dma_chan)
+{
+	struct pcl816_private *devpriv = dev->private;
+	int i;
+
+	/*
+	 * Only IRQs 2-7 are valid.
+	 * Only DMA channels 3 and 1 are valid.
+	 *
+	 * Both must be valid for async command support.
+	 */
+	if (!(irq_num >= 2 && irq_num <= 7) ||
+	    !(dma_chan == 3 || dma_chan == 1))
+		return 0;
+
+	/*
+	 * Request the IRQ and DMA channels and allocate the DMA buffers.
+	 * If the requests or allocations fail async command supprt will
+	 * not be available.
+	 */
+	if (request_irq(irq_num, pcl816_interrupt, 0, dev->board_name, dev))
+		return 0;
+	if (request_dma(dma_chan, dev->board_name)) {
+		free_irq(irq_num, dev);
+		return 0;
+	}
+
+	dev->irq = irq_num;
+	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 pcl816_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 {
 	const struct pcl816_board *board = dev->board_ptr;
 	struct pcl816_private *devpriv;
 	struct comedi_subdevice *s;
 	int ret;
-	int i;
 
 	devpriv = comedi_alloc_devpriv(dev, sizeof(*devpriv));
 	if (!devpriv)
@@ -673,39 +719,14 @@ static int pcl816_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	if (ret)
 		return ret;
 
-	/* we can use IRQ 2-7 for async command support */
-	if (it->options[1] >= 2 && it->options[1] <= 7) {
-		ret = request_irq(it->options[1], pcl816_interrupt, 0,
-				  dev->board_name, dev);
-		if (ret == 0)
-			dev->irq = it->options[1];
-	}
-
-	/* we need an IRQ to do DMA on channel 3 or 1 */
-	if (dev->irq && (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);
-		}
-	}
+	/*
+	 * An IRQ and DMA are required to support async commands.
+	 * pcl816_alloc_dma() will only fail if the DMA buffers
+	 * cannot be allocated.
+	 */
+	ret = pcl816_alloc_dma(dev, it->options[1], it->options[2]);
+	if (ret)
+		return ret;
 
 	ret = comedi_alloc_subdevices(dev, 4);
 	if (ret)
@@ -718,7 +739,7 @@ static int pcl816_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	s->maxdata	= board->ai_maxdata;
 	s->range_table	= &range_pcl816;
 	s->insn_read	= pcl816_ai_insn_read;
-	if (devpriv->dma) {
+	if (dev->irq) {
 		dev->read_subdev = s;
 		s->subdev_flags	|= SDF_CMD_READ;
 		s->len_chanlist	= board->ai_chanlist;