staging: comedi: pcl711: use comedi_subdevice 'readback'

Use the new comedi_subdevice 'readback' member and the core provided
(*insn_read) for the readback of the analog output subdevice channels.
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/pcl711.c

@@ -157,7 +157,6 @@ static const struct pcl711_board boardtypes[] = {
 
 struct pcl711_private {
 	unsigned int ntrig;
-	unsigned int ao_readback[2];
 	unsigned int divisor1;
 	unsigned int divisor2;
 };
@@ -410,31 +409,15 @@ static int pcl711_ao_insn_write(struct comedi_device *dev,
 				struct comedi_insn *insn,
 				unsigned int *data)
 {
-	struct pcl711_private *devpriv = dev->private;
 	unsigned int chan = CR_CHAN(insn->chanspec);
-	unsigned int val = devpriv->ao_readback[chan];
+	unsigned int val = s->readback[chan];
 	int i;
 
 	for (i = 0; i < insn->n; i++) {
 		val = data[i];
 		pcl711_ao_write(dev, chan, val);
 	}
-	devpriv->ao_readback[chan] = val;
-
-	return insn->n;
-}
-
-static int pcl711_ao_insn_read(struct comedi_device *dev,
-			       struct comedi_subdevice *s,
-			       struct comedi_insn *insn,
-			       unsigned int *data)
-{
-	struct pcl711_private *devpriv = dev->private;
-	unsigned int chan = CR_CHAN(insn->chanspec);
-	int i;
-
-	for (i = 0; i < insn->n; i++)
-		data[i] = devpriv->ao_readback[chan];
+	s->readback[chan] = val;
 
 	return insn->n;
 }
@@ -527,7 +510,11 @@ static int pcl711_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	s->maxdata	= 0xfff;
 	s->range_table	= &range_bipolar5;
 	s->insn_write	= pcl711_ao_insn_write;
-	s->insn_read	= pcl711_ao_insn_read;
+	s->insn_read	= comedi_readback_insn_read;
+
+	ret = comedi_alloc_subdev_readback(s);
+	if (ret)
+		return ret;
 
 	/* Digital Input subdevice */
 	s = &dev->subdevices[2];