[PATCH v2] staging: comedi: adv_pci1710: fix analog output readback value

[H Hartley Sweeten]

The last value written to a analog output channel is cached in the
private data of this driver for readback.

Currently, the wrong value is cached in the (*insn_write) functions.
The current code stores the data[n] value for readback afer the loop
has written all the values. At this time 'n' points past the end of
the data array.

Fix the functions by using a local variable to hold the data being
written to the analog output channel. This variable is then used
after the loop is complete to store the readback value. The current
value is retrieved before the loop in case no values are actually
written..

Signed-off-by: H Hartley Sweeten <hsweeten at visionengravers.com>
Cc: Ian Abbott <abbotti at mev.co.uk>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---

v2: also fix readback in pci1720_insn_write_ao() as pointed out by
    Ian Abbott

 drivers/staging/comedi/drivers/adv_pci1710.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/comedi/drivers/adv_pci1710.c b/drivers/staging/comedi/drivers/adv_pci1710.c
index 69a8298..f9d6111 100644
--- a/drivers/staging/comedi/drivers/adv_pci1710.c
+++ b/drivers/staging/comedi/drivers/adv_pci1710.c
@@ -494,6 +494,7 @@ static int pci171x_insn_write_ao(struct comedi_device *dev,
 				 struct comedi_insn *insn, unsigned int *data)
 {
 	struct pci1710_private *devpriv = dev->private;
+	unsigned int val;
 	int n, chan, range, ofs;
 
 	chan = CR_CHAN(insn->chanspec);
@@ -509,11 +510,14 @@ static int pci171x_insn_write_ao(struct comedi_device *dev,
 		outw(devpriv->da_ranges, dev->iobase + PCI171x_DAREF);
 		ofs = PCI171x_DA1;
 	}
+	val = devpriv->ao_data[chan];
 
-	for (n = 0; n < insn->n; n++)
-		outw(data[n], dev->iobase + ofs);
+	for (n = 0; n < insn->n; n++) {
+		val = data[n];
+		outw(val, dev->iobase + ofs);
+	}
 
-	devpriv->ao_data[chan] = data[n];
+	devpriv->ao_data[chan] = val;
 
 	return n;
 
@@ -679,6 +683,7 @@ static int pci1720_insn_write_ao(struct comedi_device *dev,
 				 struct comedi_insn *insn, unsigned int *data)
 {
 	struct pci1710_private *devpriv = dev->private;
+	unsigned int val;
 	int n, rangereg, chan;
 
 	chan = CR_CHAN(insn->chanspec);
@@ -688,13 +693,15 @@ static int pci1720_insn_write_ao(struct comedi_device *dev,
 		outb(rangereg, dev->iobase + PCI1720_RANGE);
 		devpriv->da_ranges = rangereg;
 	}
+	val = devpriv->ao_data[chan];
 
 	for (n = 0; n < insn->n; n++) {
-		outw(data[n], dev->iobase + PCI1720_DA0 + (chan << 1));
+		val = data[n];
+		outw(val, dev->iobase + PCI1720_DA0 + (chan << 1));
 		outb(0, dev->iobase + PCI1720_SYNCOUT);	/*  update outputs */
 	}
 
-	devpriv->ao_data[chan] = data[n];
+	devpriv->ao_data[chan] = val;
 
 	return n;
 }
-- 
1.8.5.2