staging: comedi: ni_at_ao: use subdevice readback for 'caldac'

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

Tidy up atao_calib_insn_write().

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>

1 files changed, 21 insertions, 34 deletions

diff --git a/drivers/staging/comedi/drivers/ni_at_ao.c b/drivers/staging/comedi/drivers/ni_at_ao.c
index 5fb40cd..05370a4 100644
--- a/drivers/staging/comedi/drivers/ni_at_ao.c
+++ b/drivers/staging/comedi/drivers/ni_at_ao.c
@@ -244,47 +244,31 @@ static int atao_calib_insn_write(struct comedi_device *dev,
 				 struct comedi_insn *insn,
 				 unsigned int *data)
 {
-	struct atao_private *devpriv = dev->private;
 	unsigned int chan = CR_CHAN(insn->chanspec);
-	unsigned int bitstring;
-	unsigned int val;
-	int bit;
 
-	if (insn->n == 0)
-		return 0;
+	if (insn->n) {
+		unsigned int val = data[insn->n - 1];
+		unsigned int bitstring = ((chan & 0x7) << 8) | val;
+		unsigned int bits;
+		int bit;
 
-	devpriv->caldac[chan] = data[insn->n - 1] & s->maxdata;
+		/* write the channel and last data value to the caldac */
+		/* clock the bitstring to the caldac; MSB -> LSB */
+		for (bit = 1 << 10; bit; bit >>= 1) {
+			bits = (bit & bitstring) ? ATAO_CFG2_SDATA : 0;
 
-	/* write the channel and last data value to the caldac */
-	bitstring = ((chan & 0x7) << 8) | devpriv->caldac[chan];
+			outw(bits, dev->iobase + ATAO_CFG2_REG);
+			outw(bits | ATAO_CFG2_SCLK,
+			     dev->iobase + ATAO_CFG2_REG);
+		}
 
-	/* clock the bitstring to the caldac; MSB -> LSB */
-	for (bit = 1 << 10; bit; bit >>= 1) {
-		val = (bit & bitstring) ? ATAO_CFG2_SDATA : 0;
+		/* strobe the caldac to load the value */
+		outw(ATAO_CFG2_CALLD(chan), dev->iobase + ATAO_CFG2_REG);
+		outw(ATAO_CFG2_CALLD_NOP, dev->iobase + ATAO_CFG2_REG);
 
-		outw(val, dev->iobase + ATAO_CFG2_REG);
-		outw(val | ATAO_CFG2_SCLK, dev->iobase + ATAO_CFG2_REG);
+		s->readback[chan] = val;
 	}
 
-	/* strobe the caldac to load the value */
-	outw(ATAO_CFG2_CALLD(chan), dev->iobase + ATAO_CFG2_REG);
-	outw(ATAO_CFG2_CALLD_NOP, dev->iobase + ATAO_CFG2_REG);
-
-	return insn->n;
-}
-
-static int atao_calib_insn_read(struct comedi_device *dev,
-				struct comedi_subdevice *s,
-				struct comedi_insn *insn,
-				unsigned int *data)
-{
-	struct atao_private *devpriv = dev->private;
-	unsigned int chan = CR_CHAN(insn->chanspec);
-	int i;
-
-	for (i = 0; i < insn->n; i++)
-		data[i] = devpriv->caldac[chan];
-
 	return insn->n;
 }
 
@@ -365,9 +349,12 @@ static int atao_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 	s->subdev_flags	= SDF_WRITABLE | SDF_INTERNAL;
 	s->n_chan	= (board->n_ao_chans * 2) + 1;
 	s->maxdata	= 0xff;
-	s->insn_read	= atao_calib_insn_read;
 	s->insn_write	= atao_calib_insn_write;
 
+	ret = comedi_alloc_subdev_readback(s);
+	if (ret)
+		return ret;
+
 	/* EEPROM subdevice */
 	s = &dev->subdevices[3];
 	s->type		= COMEDI_SUBD_UNUSED;