staging: comedi: ni_atmio16d: 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/ni_atmio16d.c

@@ -138,7 +138,6 @@ struct atmio16d_private {
 	enum { dac_internal, dac_external } dac0_reference, dac1_reference;
 	enum { dac_2comp, dac_straight } dac0_coding, dac1_coding;
 	const struct comedi_lrange *ao_range_type_list[2];
-	unsigned int ao_readback[2];
 	unsigned int com_reg_1_state; /* current state of command register 1 */
 	unsigned int com_reg_2_state; /* current state of command register 2 */
 };
@@ -496,18 +495,6 @@ static int atmio16d_ai_insn_read(struct comedi_device *dev,
 	return i;
 }
 
-static int atmio16d_ao_insn_read(struct comedi_device *dev,
-				 struct comedi_subdevice *s,
-				 struct comedi_insn *insn, unsigned int *data)
-{
-	struct atmio16d_private *devpriv = dev->private;
-	int i;
-
-	for (i = 0; i < insn->n; i++)
-		data[i] = devpriv->ao_readback[CR_CHAN(insn->chanspec)];
-	return i;
-}
-
 static int atmio16d_ao_insn_write(struct comedi_device *dev,
 				  struct comedi_subdevice *s,
 				  struct comedi_insn *insn,
@@ -527,7 +514,7 @@ static int atmio16d_ao_insn_write(struct comedi_device *dev,
 	for (i = 0; i < insn->n; i++) {
 		unsigned int val = data[i];
 
-		devpriv->ao_readback[chan] = val;
+		s->readback[chan] = val;
 
 		if (munge)
 			val ^= 0x800;
@@ -686,8 +673,6 @@ static int atmio16d_attach(struct comedi_device *dev,
 	s->type = COMEDI_SUBD_AO;
 	s->subdev_flags = SDF_WRITABLE;
 	s->n_chan = 2;
-	s->insn_read = atmio16d_ao_insn_read;
-	s->insn_write = atmio16d_ao_insn_write;
 	s->maxdata = 0xfff;	/* 4095 decimal */
 	s->range_table_list = devpriv->ao_range_type_list;
 	switch (devpriv->dac0_range) {
@@ -706,6 +691,12 @@ static int atmio16d_attach(struct comedi_device *dev,
 		devpriv->ao_range_type_list[1] = &range_unipolar10;
 		break;
 	}
+	s->insn_write = atmio16d_ao_insn_write;
+	s->insn_read = comedi_readback_insn_read;
+
+	ret = comedi_alloc_subdev_readback(s);
+	if (ret)
+		return ret;
 
 	/* Digital I/O */
 	s = &dev->subdevices[2];