staging: comedi: rti802: 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/rti802.c

@@ -45,24 +45,8 @@ struct rti802_private {
 		dac_2comp, dac_straight
 	} dac_coding[8];
 	const struct comedi_lrange *range_type_list[8];
-	unsigned int ao_readback[8];
 };
 
-static int rti802_ao_insn_read(struct comedi_device *dev,
-			       struct comedi_subdevice *s,
-			       struct comedi_insn *insn,
-			       unsigned int *data)
-{
-	struct rti802_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];
-
-	return insn->n;
-}
-
 static int rti802_ao_insn_write(struct comedi_device *dev,
 				struct comedi_subdevice *s,
 				struct comedi_insn *insn,
@@ -70,15 +54,14 @@ static int rti802_ao_insn_write(struct comedi_device *dev,
 {
 	struct rti802_private *devpriv = dev->private;
 	unsigned int chan = CR_CHAN(insn->chanspec);
-	unsigned int val;
 	int i;
 
 	outb(chan, dev->iobase + RTI802_SELECT);
 
 	for (i = 0; i < insn->n; i++) {
-		val = data[i];
+		unsigned int val = data[i];
 
-		devpriv->ao_readback[chan] = val;
+		s->readback[chan] = val;
 
 		/* munge offset binary to two's complement if needed */
 		if (devpriv->dac_coding[chan] == dac_2comp)
@@ -116,10 +99,14 @@ static int rti802_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	s->subdev_flags	= SDF_WRITABLE;
 	s->maxdata	= 0xfff;
 	s->n_chan	= 8;
-	s->insn_read	= rti802_ao_insn_read;
 	s->insn_write	= rti802_ao_insn_write;
-	s->range_table_list = devpriv->range_type_list;
+	s->insn_read	= comedi_readback_insn_read;
 
+	ret = comedi_alloc_subdev_readback(s);
+	if (ret)
+		return ret;
+
+	s->range_table_list = devpriv->range_type_list;
 	for (i = 0; i < 8; i++) {
 		devpriv->dac_coding[i] = (it->options[3 + 2 * i])
 			? (dac_straight) : (dac_2comp);