staging: comedi: pcl818: introduce pcl818_ai_get_fifo_sample()

To clarify the code, introduce a helper function to read the analog
input data sample from the FIFO and optionally return the channel
that the sample was for. The channel is used to check for dropped
samples.
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

@@ -417,6 +417,21 @@ static void pcl818_ai_setup_next_dma(struct comedi_device *dev,
 	devpriv->dma_runs_to_end--;
 }
 
+static unsigned int pcl818_ai_get_fifo_sample(struct comedi_device *dev,
+					      struct comedi_subdevice *s,
+					      unsigned int *chan)
+{
+	unsigned int val;
+
+	val = inb(dev->iobase + PCL818_FI_DATALO);
+	val |= (inb(dev->iobase + PCL818_FI_DATAHI) << 8);
+
+	if (chan)
+		*chan = val & 0xf;
+
+	return (val >> 4) & s->maxdata;
+}
+
 static unsigned int pcl818_ai_get_sample(struct comedi_device *dev,
 					 struct comedi_subdevice *s,
 					 unsigned int *chan)
@@ -652,14 +667,16 @@ static irqreturn_t interrupt_pcl818_ai_mode13_fifo(int irq, void *d)
 	struct comedi_device *dev = d;
 	struct pcl818_private *devpriv = dev->private;
 	struct comedi_subdevice *s = dev->read_subdev;
+	unsigned int status;
+	unsigned int chan;
+	unsigned int val;
 	int i, len;
-	unsigned char lo;
 
 	outb(0, dev->iobase + PCL818_FI_INTCLR);	/*  clear fifo int request */
 
-	lo = inb(dev->iobase + PCL818_FI_STATUS);
+	status = inb(dev->iobase + PCL818_FI_STATUS);
 
-	if (lo & 4) {
+	if (status & 4) {
 		comedi_error(dev, "A/D mode1/3 FIFO overflow!");
 		s->cancel(dev, s);
 		s->async->events |= COMEDI_CB_EOA | COMEDI_CB_ERROR;
@@ -667,7 +684,7 @@ static irqreturn_t interrupt_pcl818_ai_mode13_fifo(int irq, void *d)
 		return IRQ_HANDLED;
 	}
 
-	if (lo & 1) {
+	if (status & 1) {
 		comedi_error(dev, "A/D mode1/3 FIFO interrupt without data!");
 		s->cancel(dev, s);
 		s->async->events |= COMEDI_CB_EOA | COMEDI_CB_ERROR;
@@ -675,17 +692,17 @@ static irqreturn_t interrupt_pcl818_ai_mode13_fifo(int irq, void *d)
 		return IRQ_HANDLED;
 	}
 
-	if (lo & 2)
+	if (status & 2)
 		len = 512;
 	else
 		len = 0;
 
 	for (i = 0; i < len; i++) {
-		lo = inb(dev->iobase + PCL818_FI_DATALO);
-		if ((lo & 0xf) != devpriv->act_chanlist[devpriv->act_chanlist_pos]) {	/*  dropout! */
+		val = pcl818_ai_get_fifo_sample(dev, s, &chan);
+		if (chan != devpriv->act_chanlist[devpriv->act_chanlist_pos]) {
 			dev_dbg(dev->class_dev,
 				"A/D mode1/3 FIFO - channel dropout %d!=%d !\n",
-				(lo & 0xf),
+				chan,
 				devpriv->act_chanlist[devpriv->act_chanlist_pos]);
 			s->cancel(dev, s);
 			s->async->events |= COMEDI_CB_EOA | COMEDI_CB_ERROR;
@@ -693,7 +710,7 @@ static irqreturn_t interrupt_pcl818_ai_mode13_fifo(int irq, void *d)
 			return IRQ_HANDLED;
 		}
 
-		comedi_buf_put(s->async, (lo >> 4) | (inb(dev->iobase + PCL818_FI_DATAHI) << 4));	/*  get one sample */
+		comedi_buf_put(s->async, val);
 
 		if (!pcl818_ai_next_chan(dev, s))
 			return IRQ_HANDLED;