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 <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/adv_pci1724.c b/drivers/staging/comedi/drivers/adv_pci1724.c
index 7bbd36a..4aa1631 100644 (file)
--- 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;
        }