[PATCH 11/14] staging: comedi: multiq3: tidy up multiq3_encoder_insn_read()

[H Hartley Sweeten]

Encoders are not a "normal" subdevice in comedi. For aesthetics, tidy
up this function and add a couple comments to clarify the function.

Remove the strange munging of the data. The encoder data is decoded
in quadrature and used to increment or decrement a 24-bit counter.
Adding 0x800000 to the counter value doesn't make any sense.

Signed-off-by: H Hartley Sweeten <hsweeten at visionengravers.com>
Cc: Ian Abbott <abbotti at mev.co.uk>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 drivers/staging/comedi/drivers/multiq3.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/drivers/staging/comedi/drivers/multiq3.c b/drivers/staging/comedi/drivers/multiq3.c
index b5d2354..955f75a 100644
--- a/drivers/staging/comedi/drivers/multiq3.c
+++ b/drivers/staging/comedi/drivers/multiq3.c
@@ -185,22 +185,30 @@ static int multiq3_encoder_insn_read(struct comedi_device *dev,
 				     struct comedi_insn *insn,
 				     unsigned int *data)
 {
-	int chan = CR_CHAN(insn->chanspec);
-	int value;
-	int n;
+	unsigned int chan = CR_CHAN(insn->chanspec);
+	unsigned int val;
+	int i;
 
-	for (n = 0; n < insn->n; n++) {
+	for (i = 0; i < insn->n; i++) {
+		/* select encoder channel */
 		multiq3_set_ctrl(dev, MULTIQ3_CTRL_EN |
 				      MULTIQ3_CTRL_E_CHAN(chan));
+
+		/* reset the byte pointer */
 		outb(MULTIQ3_BP_RESET, dev->iobase + MULTIQ3_ENC_CTRL_REG);
+
+		/* latch the data */
 		outb(MULTIQ3_TRSFRCNTR_OL, dev->iobase + MULTIQ3_ENC_CTRL_REG);
-		value = inb(dev->iobase + MULTIQ3_ENC_DATA_REG);
-		value |= (inb(dev->iobase + MULTIQ3_ENC_DATA_REG) << 8);
-		value |= (inb(dev->iobase + MULTIQ3_ENC_DATA_REG) << 16);
-		data[n] = (value + 0x800000) & 0xffffff;
+
+		/* read the 24-bit encoder data (lsb/mid/msb) */
+		val = inb(dev->iobase + MULTIQ3_ENC_DATA_REG);
+		val |= (inb(dev->iobase + MULTIQ3_ENC_DATA_REG) << 8);
+		val |= (inb(dev->iobase + MULTIQ3_ENC_DATA_REG) << 16);
+
+		data[i] = val;
 	}
 
-	return n;
+	return insn->n;
 }
 
 static void multiq3_encoder_reset(struct comedi_device *dev,
-- 
2.5.1