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

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Message-ID: <20200427151214.GA6389@arch>
Date:   Mon, 27 Apr 2020 17:12:14 +0200
From:   Tomasz Duszynski <tomasz.duszynski@...akon.com>
To:     Andreas Klinger <ak@...klinger.de>
CC:     <jic23@...nel.org>, <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] 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 <ak@...klinger.de>
> ---
>  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