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staging: comedi: pcmda12: cleanup pcmda12_ao_insn_read()

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Remove the boilerplate comment from the 'skel' driver.

To initiate the simultaneaous transfer, only one analog output
register needs to be read. Move the read out of the for() loop.

(*insn_read) functions should return an errno or the number of
samples actually read. Change the final return to insn->n to
make this clear.

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>
This commit is contained in:
H Hartley Sweeten
2013-06-03 19:04:45 -07:00
committed by Greg Kroah-Hartman
parent b11c5d3ccc
commit cac10bf92a
1 changed files with 10 additions and 19 deletions
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29
drivers/staging/comedi/drivers/pcmda12.c
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@@ -117,35 +117,26 @@ static int pcmda12_ao_insn_write(struct comedi_device *dev,
return i;
}
/* AO subdevices should have a read insn as well as a write insn.
Usually this means copying a value stored in devpriv->ao_readback.
However, since this driver supports simultaneous xfer then sometimes
this function actually accomplishes work.
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 pcmda12_ao_insn_read(struct comedi_device *dev,
struct comedi_subdevice *s,
struct comedi_insn *insn,
unsigned int *data)
{
struct pcmda12_private *devpriv = dev->private;
unsigned int chan = CR_CHAN(insn->chanspec);
int i;
int chan = CR_CHAN(insn->chanspec);
for (i = 0; i < insn->n; i++) {
if (devpriv->simultaneous_xfer_mode)
inb(LSB_PORT(chan));
/* read back shadow register */
/*
* Initiate simultaneaous xfer mode by reading one of the
* AO registers. All analog outputs will then be updated.
*/
if (devpriv->simultaneous_xfer_mode)
inb(LSB_PORT(chan));
for (i = 0; i < insn->n; i++)
data[i] = devpriv->ao_readback[chan];
}
return i;
return insn->n;
}
static int pcmda12_attach(struct comedi_device *dev,