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staging: comedi: ni_660x: tidy up ni_660x_dio_insn_bits()

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Use some local variables to clarify this function.

This (*insn_bits) function is a bit different from most comedi drivers.
Add some comments to clarify why the shifts are used.

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 2016-03-22 11:10:32 -07:00 committed by Greg Kroah-Hartman
parent 7e90618694
commit 826f783a0e
1 changed files with 20 additions and 11 deletions

31
drivers/staging/comedi/drivers/ni_660x.c

@ -780,21 +780,30 @@ static void init_tio_chip(struct comedi_device *dev, int chipset)
static int ni_660x_dio_insn_bits(struct comedi_device *dev,
struct comedi_subdevice *s,
struct comedi_insn *insn, unsigned int *data)
struct comedi_insn *insn,
unsigned int *data)
{
unsigned int base_bitfield_channel = CR_CHAN(insn->chanspec);
unsigned int shift = CR_CHAN(insn->chanspec);
unsigned int mask = data[0] << shift;
unsigned int bits = data[1] << shift;
/* Check if we have to write some bits */
if (data[0]) {
s->state &= ~(data[0] << base_bitfield_channel);
s->state |= (data[0] & data[1]) << base_bitfield_channel;
/* Write out the new digital output lines */
/*
* There are 40 channels in this subdevice but only 32 are usable
* as DIO. The shift adjusts the mask/bits to account for the base
* channel in insn->chanspec. The state update can then be handled
* normally for the 32 usable channels.
*/
if (mask) {
s->state &= ~mask;
s->state |= (bits & mask);
ni_660x_write(dev, 0, s->state, NI660X_DIO32_OUTPUT);
}
/* on return, data[1] contains the value of the digital
* input and output lines. */
data[1] = (ni_660x_read(dev, 0, NI660X_DIO32_INPUT) >>
base_bitfield_channel);
/*
* Return the input channels, shifted back to account for the base
* channel.
*/
data[1] = ni_660x_read(dev, 0, NI660X_DIO32_INPUT) >> shift;
return insn->n;
}