[PATCH 4/5] staging: comedi: comedidev.h: fix comedi_offset_munge() for values > s->maxdata

[H Hartley Sweeten]

The comedi_offset_munge() helper is used to convert unsigned int data
values from the comedi offset binary format to two's complement values
for hardware that needs the data in that format. The comedi data is
always checked against s->maxdata before writing to the hardware so
the current implementation always works correctly.

It also works to convert the hardware two's complement data into the
offset binary format used by comedi. Unfortunately, some boards
return extra data in the upper bits. The current implementation
ends up leaving these bits in the converted value.

Mask the converted value to ensure that any extra bits are removed.

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/comedidev.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
index 28a5d3a..1c8ed5d 100644
--- a/drivers/staging/comedi/comedidev.h
+++ b/drivers/staging/comedi/comedidev.h
@@ -388,7 +388,7 @@ static inline bool comedi_chan_range_is_external(struct comedi_subdevice *s,
 static inline unsigned int comedi_offset_munge(struct comedi_subdevice *s,
 					       unsigned int val)
 {
-	return val ^ s->maxdata ^ (s->maxdata >> 1);
+	return (val ^ s->maxdata ^ (s->maxdata >> 1)) & s->maxdata;
 }
 
 /**
-- 
2.4.3