On Mon, Sep 28, 2015 at 2:08 AM, Jonathan Cameron <jic23@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > On 27 September 2015 23:35:29 BST, Matt Ranostay <mranostay@xxxxxxxxx> wrote: >>On Sun, Sep 27, 2015 at 6:29 AM, Jonathan Cameron <jic23@xxxxxxxxxx> >>wrote: >>> On 27/09/15 07:18, Matt Ranostay wrote: >>>> Previous offset wasn't applied in the correct order and invalid. >>>> This patchset fixes this issue, and also has the correct scale value >>>> applied to the offset. >>>> >>>> Signed-off-by: Matt Ranostay <mranostay@xxxxxxxxx> >>> Oops, missed that. >>> >>> Given it's provided in the datasheet as effectively a fractional >>value >>> would val = -40000, val2 = 65536 and type = IIO_FRACTIONAL not be >>cleaner >>> and give the same answer? >>> >>Actually not because the way the datasheet states it ((value / 2**16) >>* 165) - 40, so the scale value needs to be applied to the -40 >>offset (165/65536) > Good point. Can't we do (-40*165)/65536 ? Nope. scale = 165<<2 / 65536 offset = 40 / scale Maybe we should add a new IIO_CHAN_INFO_SCALED_OFFSET that uses the scale value and a divisor that returns an IIO_FRACTIONAL? >> >>> Speaking of which, for the scale are we loosing any precision by >>shifting >>> the bottom of the fraction right 2 rather than the top left 2 which >>would have >>> the same result? >> >>Ah possibly. But I suspect isn't anything measurable... >> >>> >>> Jonathan >>>> --- >>>> drivers/iio/humidity/hdc100x.c | 5 +++-- >>>> 1 file changed, 3 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/iio/humidity/hdc100x.c >>b/drivers/iio/humidity/hdc100x.c >>>> index 2824578..a7f61e8 100644 >>>> --- a/drivers/iio/humidity/hdc100x.c >>>> +++ b/drivers/iio/humidity/hdc100x.c >>>> @@ -221,8 +221,9 @@ static int hdc100x_read_raw(struct iio_dev >>*indio_dev, >>>> } >>>> break; >>>> case IIO_CHAN_INFO_OFFSET: >>>> - *val = -40; >>>> - return IIO_VAL_INT; >>>> + *val = -3971; >>>> + *val2 = 879096; >>>> + return IIO_VAL_INT_PLUS_MICRO; >>>> default: >>>> return -EINVAL; >>>> } >>>> >>> > > -- > Sent from my Android device with K-9 Mail. Please excuse my brevity. -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
