staging: comedi: ni_660x: tidy up ni_660x_dio_insn_bits()

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;

}