linux-kernel - Re: [PATCH v2] iio: bmp280: fix compensation of humidity

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Message-ID: <20200503140553.2152709b@archlinux>
Date:   Sun, 3 May 2020 14:05:53 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andreas Klinger <ak@...klinger.de>
Cc:     knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
        bgolaszewski@...libre.com, linus.walleij@...aro.org,
        tglx@...utronix.de, allison@...utok.net, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iio: bmp280: fix compensation of humidity

On Wed, 29 Apr 2020 20:48:54 +0200
Andreas Klinger <ak@...klinger.de> 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 <ak@...klinger.de>

> ---

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;
>  };
>