staging: comedi: daqboard2000: 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.

For aesthetics, tidy up the (*insn_write) a bit.
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/daqboard2000.c

@@ -275,7 +275,6 @@ struct daqboard2000_private {
 		card_daqboard_2000
 	} card;
 	void __iomem *plx;
-	unsigned int ao_readback[2];
 };
 
 static void writeAcqScanListEntry(struct comedi_device *dev, u16 entry)
@@ -401,21 +400,6 @@ static int daqboard2000_ai_insn_read(struct comedi_device *dev,
 	return i;
 }
 
-static int daqboard2000_ao_insn_read(struct comedi_device *dev,
-				     struct comedi_subdevice *s,
-				     struct comedi_insn *insn,
-				     unsigned int *data)
-{
-	struct daqboard2000_private *devpriv = dev->private;
-	int chan = CR_CHAN(insn->chanspec);
-	int i;
-
-	for (i = 0; i < insn->n; i++)
-		data[i] = devpriv->ao_readback[chan];
-
-	return i;
-}
-
 static int daqboard2000_ao_eoc(struct comedi_device *dev,
 			       struct comedi_subdevice *s,
 			       struct comedi_insn *insn,
@@ -435,22 +419,23 @@ static int daqboard2000_ao_insn_write(struct comedi_device *dev,
 				      struct comedi_insn *insn,
 				      unsigned int *data)
 {
-	struct daqboard2000_private *devpriv = dev->private;
-	int chan = CR_CHAN(insn->chanspec);
-	int ret;
+	unsigned int chan = CR_CHAN(insn->chanspec);
 	int i;
 
 	for (i = 0; i < insn->n; i++) {
-		writew(data[i], dev->mmio + dacSetting(chan));
+		unsigned int val = data[i];
+		int ret;
+
+		writew(val, dev->mmio + dacSetting(chan));
 
 		ret = comedi_timeout(dev, s, insn, daqboard2000_ao_eoc, 0);
 		if (ret)
 			return ret;
 
-		devpriv->ao_readback[chan] = data[i];
+		s->readback[chan] = val;
 	}
 
-	return i;
+	return insn->n;
 }
 
 static void daqboard2000_resetLocalBus(struct comedi_device *dev)
@@ -721,10 +706,14 @@ static int daqboard2000_auto_attach(struct comedi_device *dev,
 	s->subdev_flags = SDF_WRITABLE;
 	s->n_chan = 2;
 	s->maxdata = 0xffff;
-	s->insn_read = daqboard2000_ao_insn_read;
 	s->insn_write = daqboard2000_ao_insn_write;
+	s->insn_read = comedi_readback_insn_read;
 	s->range_table = &range_bipolar10;
 
+	result = comedi_alloc_subdev_readback(s);
+	if (result)
+		return result;
+
 	s = &dev->subdevices[2];
 	result = subdev_8255_init(dev, s, daqboard2000_8255_cb,
 				  dioP2ExpansionIO8Bit);