staging: comedi: cb_pcimdda: cleanup the analog out read/write

Use the register map define to work out the i/o address.

Cleanup the comments about the simultaneous transfer mode for
the analog outputs.

Change the return to 'insn->n', the comedi core expects the return
to be the number of data elements used. Technically the 'i' value
is correct but 'insn->n' just makes it clearer.

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

diff --git a/drivers/staging/comedi/drivers/cb_pcimdda.c b/drivers/staging/comedi/drivers/cb_pcimdda.c
index a5e055f0a5ffc3bb9192554c22a23a37583cfc93..350c8078cded4c5840d4483dd6663e7d668d7d79 100644 (file)
--- a/drivers/staging/comedi/drivers/cb_pcimdda.c
+++ b/drivers/staging/comedi/drivers/cb_pcimdda.c
@@ -110,62 +110,51 @@ static int cb_pcimdda_ao_winsn(struct comedi_device *dev,
                               unsigned int *data)
 {
        struct cb_pcimdda_private *devpriv = dev->private;
+       unsigned int chan = CR_CHAN(insn->chanspec);
+       unsigned long offset = dev->iobase + PCIMDDA_DA_CHAN(chan);
+       unsigned int val = 0;
        int i;
-       int chan = CR_CHAN(insn->chanspec);
-       unsigned long offset = dev->iobase + chan * 2;
 
-       /* Writing a list of values to an AO channel is probably not
-        * very useful, but that's how the interface is defined. */
        for (i = 0; i < insn->n; i++) {
-               /*  first, load the low byte */
-               outb((char)(data[i] & 0x00ff), offset);
-               /*  next, write the high byte -- only after this is written is
-                  the channel voltage updated in the DAC, unless
-                  we're in simultaneous xfer mode (jumper on card)
-                  then a rinsn is necessary to actually update the DAC --
-                  see cb_pcimdda_ao_rinsn() below... */
-               outb((char)(data[i] >> 8 & 0x00ff), offset + 1);
-
-               /* for testing only.. the actual rinsn SHOULD do an inw!
-                  (see the stuff about simultaneous XFER mode on this board) */
-               devpriv->ao_readback[chan] = data[i];
+               val = data[i];
+
+               /*
+                * Write the LSB then MSB.
+                *
+                * If the simultaneous xfer mode is selected by the
+                * jumper on the card, a read instruction is needed
+                * in order to initiate the simultaneous transfer.
+                * Otherwise, the DAC will be updated when the MSB
+                * is written.
+                */
+               outb(val & 0x00ff, offset);
+               outb((val >> 8) & 0x00ff, offset + 1);
        }
 
-       /* return the number of samples read/written */
-       return i;
-}
+       /* Cache the last value for readback */
+       devpriv->ao_readback[chan] = val;
 
-/* AO subdevices should have a read insn as well as a write insn.
+       return insn->n;
+}
 
-   Usually this means copying a value stored in devpriv->ao_readback.
-   However, since this board has this jumper setting called "Simultaneous
-   Xfer mode" (off by default), we will support it.  Simultaneaous xfer
-   mode is accomplished by loading ALL the values you want for AO in all the
-   channels, then READing off one of the AO registers to initiate the
-   instantaneous simultaneous update of all DAC outputs, which makes
-   all AO channels update simultaneously.  This is useful for some control
-   applications, I would imagine.
-*/
 static int cb_pcimdda_ao_rinsn(struct comedi_device *dev,
                               struct comedi_subdevice *s,
                               struct comedi_insn *insn,
                               unsigned int *data)
 {
        struct cb_pcimdda_private *devpriv = dev->private;
-       int i;
        int chan = CR_CHAN(insn->chanspec);
+       unsigned long offset = dev->iobase + PCIMDDA_DA_CHAN(chan);
+       int i;
 
        for (i = 0; i < insn->n; i++) {
-               inw(dev->iobase + chan * 2);
-               /*
-                * should I set data[i] to the result of the actual read
-                * on the register or the cached unsigned int in
-                * devpriv->ao_readback[]?
-                */
+               /* Initiate the simultaneous transfer */
+               inw(offset);
+
                data[i] = devpriv->ao_readback[chan];
        }
 
-       return i;
+       return insn->n;
 }
 
 static struct pci_dev *cb_pcimdda_probe(struct comedi_device *dev,