2020-04-29 18:51:24

by Andreas Klinger

Subject: [PATCH v2] 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.

Change to v1:
Thanks to Tomasz for suggesting the easier to use function clamp_val()
which is now used.

Signed-off-by: Andreas Klinger <[email protected]>
---
drivers/iio/pressure/bmp280-core.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
index 29c209cc1108..297ee2205bf6 100644
--- a/drivers/iio/pressure/bmp280-core.c
+++ b/drivers/iio/pressure/bmp280-core.c
@@ -271,6 +271,8 @@ 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 = clamp_val(var, 0, 419430400);
+
return var >> 12;
};

--
2.20.1

2020-05-03 13:07:57

by Jonathan Cameron

Subject: Re: [PATCH v2] iio: bmp280: fix compensation of humidity

On Wed, 29 Apr 2020 20:48:54 +0200
Andreas Klinger <[email protected]> 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.

More details needed...

1. Fixes tag
2. What is the result of this not being clamped? What happens if I set
a value outside that range?
>
> Change to v1:
> Thanks to Tomasz for suggesting the easier to use function clamp_val()
> which is now used.

Change log belongs below the ---
>
> Signed-off-by: Andreas Klinger <[email protected]>

> ---

Here for changelog.

> drivers/iio/pressure/bmp280-core.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
> index 29c209cc1108..297ee2205bf6 100644
> --- a/drivers/iio/pressure/bmp280-core.c
> +++ b/drivers/iio/pressure/bmp280-core.c
> @@ -271,6 +271,8 @@ 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 = clamp_val(var, 0, 419430400);
> +
> return var >> 12;
> };
>