Re: [PATCH 1/3] iio:humidity:si7020: replaced bitmask on humidity values with range check

[Hartmut Knaack <knaack.h@gmx.de>]

Nicola Corna schrieb am 20.08.2015 um 16:11:
> The maximum possible value for the relative humidity is 55575 (100%RH).
> This value, if shifted right by 2 bits, uses 14 bits and masking it with
> a 12 bit mask removes 2 meaningful bits.
> The masking has been replaced with a range check that sets the minimum
> value at 3194 (0%RH) and the maximum at 55575 (100%RH).

Hmm, I guess the mask should have been applied for bits 13:2, but your
solution confirms better to the data sheet. Just one essential detail:
The raw sensor data has already been divided by 4 when you do the boundary
check. So, you need to divide the boundaries, as well.
Btw, you can make this a one-liner using clamp_val, check it out: [1]

[1]http://lxr.free-electrons.com/source/include/linux/kernel.h#L795

> 
> Signed-off-by: Nicola Corna <nicola@corna.info>
> ---
>  drivers/iio/humidity/si7020.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
> index fa3b809..62fdbcf 100644
> --- a/drivers/iio/humidity/si7020.c
> +++ b/drivers/iio/humidity/si7020.c
> @@ -57,8 +57,16 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
>  		if (ret < 0)
>  			return ret;
>  		*val = ret >> 2;
> -		if (chan->type == IIO_HUMIDITYRELATIVE)
> -			*val &= GENMASK(11, 0);
> +		/*
> +		 * Humidity values can sligthly exceed the 0-100%RH
> +		 * range and should be corrected by software
> +		 */
> +		if (chan->type == IIO_HUMIDITYRELATIVE) {
> +			if (*val < 3194) /* 0%RH */
> +				*val = 3194;
> +			else if (*val > 55575) /* 100%RH */
> +				*val = 55575;
> +		}
>  		return IIO_VAL_INT;
>  	case IIO_CHAN_INFO_SCALE:
>  		if (chan->type == IIO_TEMP)
>