staging: comedi: adv_pci1724: use subdevice readback for 'offset_value'

Use the comedi_subdevice 'readback' member and the core provided (*insn_read)
to handle the readback of the write-only offset calib subdevice. Remove the
then unused 'offset_value' member from the private data.

Signed-off-by: H Hartley Sweeten <[email protected]>
Reviewed-by: Ian Abbott <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

1 files changed, 6 insertions, 25 deletions

diff --git a/drivers/staging/comedi/drivers/adv_pci1724.c b/drivers/staging/comedi/drivers/adv_pci1724.c
index 7bbd36ae0791..4aa1631de547 100644
--- a/drivers/staging/comedi/drivers/adv_pci1724.c
+++ b/drivers/staging/comedi/drivers/adv_pci1724.c
@@ -127,7 +127,6 @@ static const struct comedi_lrange ao_ranges_1724 = {
 
 /* this structure is for data unique to this hardware driver. */
 struct adv_pci1724_private {
-	int offset_value[NUM_AO_CHANNELS];
 	int gain_value[NUM_AO_CHANNELS];
 };
 
@@ -189,7 +188,6 @@ static int offset_write_insn(struct comedi_device *dev,
 			     struct comedi_subdevice *s,
 			     struct comedi_insn *insn, unsigned int *data)
 {
-	struct adv_pci1724_private *devpriv = dev->private;
 	int channel = CR_CHAN(insn->chanspec);
 	int retval;
 	int i;
@@ -201,27 +199,8 @@ static int offset_write_insn(struct comedi_device *dev,
 		retval = set_dac(dev, DAC_OFFSET_MODE, channel, data[i]);
 		if (retval < 0)
 			return retval;
-		devpriv->offset_value[channel] = data[i];
-	}
-
-	return insn->n;
-}
-
-static int offset_read_insn(struct comedi_device *dev,
-			    struct comedi_subdevice *s,
-			    struct comedi_insn *insn, unsigned int *data)
-{
-	struct adv_pci1724_private *devpriv = dev->private;
-	unsigned int channel = CR_CHAN(insn->chanspec);
-	int i;
-
-	if (devpriv->offset_value[channel] < 0) {
-		dev_err(dev->class_dev,
-			"Cannot read back channels which have not yet been written to\n");
-		return -EIO;
+		s->readback[channel] = data[i];
 	}
-	for (i = 0; i < insn->n; i++)
-		data[i] = devpriv->offset_value[channel];
 
 	return insn->n;
 }
@@ -296,9 +275,12 @@ static int setup_subdevices(struct comedi_device *dev)
 	s->type = COMEDI_SUBD_CALIB;
 	s->subdev_flags = SDF_READABLE | SDF_WRITABLE | SDF_INTERNAL;
 	s->n_chan = NUM_AO_CHANNELS;
-	s->insn_read = offset_read_insn;
-	s->insn_write = offset_write_insn;
 	s->maxdata = 0x3fff;
+	s->insn_write = offset_write_insn;
+
+	ret = comedi_alloc_subdev_readback(s);
+	if (ret)
+		return ret;
 
 	/* gain calibration */
 	s = &dev->subdevices[2];
@@ -328,7 +310,6 @@ static int adv_pci1724_auto_attach(struct comedi_device *dev,
 	/* init software copies of output values to indicate we don't know
 	 * what the output value is since it has never been written. */
 	for (i = 0; i < NUM_AO_CHANNELS; ++i) {
-		devpriv->offset_value[i] = -1;
 		devpriv->gain_value[i] = -1;
 	}