2020-04-27 14:03:57

by Andreas Klinger

Subject: [PATCH] iio: bmp280: fix compensation of humidity

Output of humidity compensation is limited to the range between 0 and 100
percent. Add this to the compensation formula as described in the datasheet
chapter 4.2.3.

Signed-off-by: Andreas Klinger <[email protected]>
---
drivers/iio/pressure/bmp280-core.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
index 29c209cc1108..ac9ef1b63b07 100644
--- a/drivers/iio/pressure/bmp280-core.c
+++ b/drivers/iio/pressure/bmp280-core.c
@@ -271,6 +271,9 @@ static u32 bmp280_compensate_humidity(struct bmp280_data *data,
+ (s32)2097152) * calib->H2 + 8192) >> 14);
var -= ((((var >> 15) * (var >> 15)) >> 7) * (s32)calib->H1) >> 4;

+ var = var < 0 ? 0 : var;
+ var = var > 419430400 ? 419430400 : var;
+
return var >> 12;
};

--
2.20.1

2020-04-27 15:19:19

by Tomasz Duszynski

Subject: Re: [PATCH] iio: bmp280: fix compensation of humidity

On Mon, Apr 27, 2020 at 04:00:19PM +0200, Andreas Klinger wrote:
> Output of humidity compensation is limited to the range between 0 and 100
> percent. Add this to the compensation formula as described in the datasheet
> chapter 4.2.3.
>
> Signed-off-by: Andreas Klinger <[email protected]>
> ---
> drivers/iio/pressure/bmp280-core.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
> index 29c209cc1108..ac9ef1b63b07 100644
> --- a/drivers/iio/pressure/bmp280-core.c
> +++ b/drivers/iio/pressure/bmp280-core.c
> @@ -271,6 +271,9 @@ static u32 bmp280_compensate_humidity(struct bmp280_data *data,
> + (s32)2097152) * calib->H2 + 8192) >> 14);
> var -= ((((var >> 15) * (var >> 15)) >> 7) * (s32)calib->H1) >> 4;
>
> + var = var < 0 ? 0 : var;
> + var = var > 419430400 ? 419430400 : var;
> +

Looks that clamp_val() might come in handy here.

> return var >> 12;
> };
>
> --
> 2.20.1