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@xxxxxxxxxxxxxxxxxxx>
Cc: Ian Abbott <abbotti@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/staging/comedi/drivers/ni_660x.c | 31 ++++++++++++++++++++-----------
1 file changed, 20 insertions(+), 11 deletions(-)
diff --git a/drivers/staging/comedi/drivers/ni_660x.c b/drivers/staging/comedi/drivers/ni_660x.c
index f24009c..f614927 100644
--- a/drivers/staging/comedi/drivers/ni_660x.c
+++ b/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;
}
--
2.6.3
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