staging: comedi: ni_labpc: allow board to attach without dma

If the dma channel is not available this driver will still work
with interrupts for the analog input subdevice command support.

In addition, only dma channels 1 and 3 are valid for the ISA
devices.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ni_labpc.c

@@ -1673,30 +1673,23 @@ int labpc_common_attach(struct comedi_device *dev, unsigned long iobase,
 	}
 
 #ifdef CONFIG_ISA_DMA_API
-	/* grab dma channel */
-	if (dma_chan > 3) {
-		dev_err(dev->class_dev, "invalid dma channel %u\n", dma_chan);
-		return -EINVAL;
-	} else if (dma_chan) {
-		unsigned long dma_flags;
-
-		/* allocate dma buffer */
+	if (dma_chan == 1 || dma_chan == 3) {
 		devpriv->dma_buffer = kmalloc(dma_buffer_size,
 					      GFP_KERNEL | GFP_DMA);
-		if (devpriv->dma_buffer == NULL)
-			return -ENOMEM;
-
-		if (request_dma(dma_chan, dev->board_name)) {
-			dev_err(dev->class_dev,
-				"failed to allocate dma channel %u\n",
-				dma_chan);
-			return -EINVAL;
+		if (devpriv->dma_buffer) {
+			ret = request_dma(dma_chan, dev->board_name);
+			if (ret == 0) {
+				unsigned long dma_flags;
+
+				devpriv->dma_chan = dma_chan;
+				dma_flags = claim_dma_lock();
+				disable_dma(devpriv->dma_chan);
+				set_dma_mode(devpriv->dma_chan, DMA_MODE_READ);
+				release_dma_lock(dma_flags);
+			} else {
+				kfree(devpriv->dma_buffer);
+			}
 		}
-		devpriv->dma_chan = dma_chan;
-		dma_flags = claim_dma_lock();
-		disable_dma(devpriv->dma_chan);
-		set_dma_mode(devpriv->dma_chan, DMA_MODE_READ);
-		release_dma_lock(dma_flags);
 	}
 #endif