staging: comedi: rtd520: sample types are unsigned

Sample values in comedi are generally represented as unsigned values.
Use unsigned types for sample value manipulations in the "rtd520" driver
for consistency.

Also replace the hand-coded munging of 2's complement sample values with
calls to `comedi_offset_munge()` and AND with `s->maxdata` to strip off
any extra sign bits.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/rtd520.c

@@ -602,7 +602,7 @@ static int rtd_ai_rinsn(struct comedi_device *dev,
 
 	/* convert n samples */
 	for (n = 0; n < insn->n; n++) {
-		s16 d;
+		unsigned short d;
 		/* trigger conversion */
 		writew(0, devpriv->las0 + LAS0_ADC);
 
@@ -621,9 +621,8 @@ static int rtd_ai_rinsn(struct comedi_device *dev,
 		d = d >> 3;	/* low 3 bits are marker lines */
 		if (CHAN_ARRAY_TEST(devpriv->chan_is_bipolar, 0))
 			/* convert to comedi unsigned data */
-			data[n] = d + 2048;
-		else
-			data[n] = d;
+			d = comedi_offset_munge(s, d);
+		data[n] = d & s->maxdata;
 	}
 
 	/* return the number of samples read/written */
@@ -643,8 +642,7 @@ static int ai_read_n(struct comedi_device *dev, struct comedi_subdevice *s,
 	int ii;
 
 	for (ii = 0; ii < count; ii++) {
-		short sample;
-		s16 d;
+		unsigned short d;
 
 		if (0 == devpriv->ai_count) {	/* done */
 			d = readw(devpriv->las1 + LAS1_ADC_FIFO);
@@ -654,13 +652,12 @@ static int ai_read_n(struct comedi_device *dev, struct comedi_subdevice *s,
 		d = readw(devpriv->las1 + LAS1_ADC_FIFO);
 		d = d >> 3;	/* low 3 bits are marker lines */
 		if (CHAN_ARRAY_TEST(devpriv->chan_is_bipolar,
-				    s->async->cur_chan)) {
+				    s->async->cur_chan))
 			/* convert to comedi unsigned data */
-			sample = d + 2048;
-		} else
-			sample = d;
+			d = comedi_offset_munge(s, d);
+		d &= s->maxdata;
 
-		if (!comedi_buf_put(s->async, sample))
+		if (!comedi_buf_put(s->async, d))
 			return -1;
 
 		if (devpriv->ai_count > 0)	/* < 0, means read forever */
@@ -677,8 +674,7 @@ static int ai_read_dregs(struct comedi_device *dev, struct comedi_subdevice *s)
 	struct rtd_private *devpriv = dev->private;
 
 	while (readl(devpriv->las0 + LAS0_ADC) & FS_ADC_NOT_EMPTY) {
-		short sample;
-		s16 d = readw(devpriv->las1 + LAS1_ADC_FIFO);
+		unsigned short d = readw(devpriv->las1 + LAS1_ADC_FIFO);
 
 		if (0 == devpriv->ai_count) {	/* done */
 			continue;	/* read rest */
@@ -686,13 +682,12 @@ static int ai_read_dregs(struct comedi_device *dev, struct comedi_subdevice *s)
 
 		d = d >> 3;	/* low 3 bits are marker lines */
 		if (CHAN_ARRAY_TEST(devpriv->chan_is_bipolar,
-				    s->async->cur_chan)) {
+				    s->async->cur_chan))
 			/* convert to comedi unsigned data */
-			sample = d + 2048;
-		} else
-			sample = d;
+			d = comedi_offset_munge(s, d);
+		d &= s->maxdata;
 
-		if (!comedi_buf_put(s->async, sample))
+		if (!comedi_buf_put(s->async, d))
 			return -1;
 
 		if (devpriv->ai_count > 0)	/* < 0, means read forever */