The line above makes vel a 12-bit quantity (st->rx[] is u8). The intention is to sign-extend vel using bit 11 as the sign bit. But because of C's promotion rules "vel = (vel << 4) >> 4;" is actually a no-op, since vel is promoted to int before the inner shift. sign_extend32 works equally well for 8 and 16 bits types, so use that. Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> --- drivers/staging/iio/resolver/ad2s1200.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/staging/iio/resolver/ad2s1200.c b/drivers/staging/iio/resolver/ad2s1200.c index 017d2f8379b7..c17893b4918c 100644 --- a/drivers/staging/iio/resolver/ad2s1200.c +++ b/drivers/staging/iio/resolver/ad2s1200.c @@ -18,6 +18,7 @@ #include <linux/delay.h> #include <linux/gpio.h> #include <linux/module.h> +#include <linux/bitops.h> #include <linux/iio/iio.h> #include <linux/iio/sysfs.h> @@ -68,7 +69,7 @@ static int ad2s1200_read_raw(struct iio_dev *indio_dev, break; case IIO_ANGL_VEL: vel = (((s16)(st->rx[0])) << 4) | ((st->rx[1] & 0xF0) >> 4); - vel = (vel << 4) >> 4; + vel = sign_extend32(vel, 11); *val = vel; break; default: -- 2.1.3 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
