linux-kernel - Re: [PATCH v2 11/16] hwmon: (mr75203) add protection for negative voltage value

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Date:   Thu, 18 Aug 2022 13:13:59 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Eliav Farber <farbere@...zon.com>
Cc:     jdelvare@...e.com, robh+dt@...nel.org, mark.rutland@....com,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, talel@...zon.com, hhhawa@...zon.com,
        jonnyc@...zon.com, hanochu@...zon.com, ronenk@...zon.com,
        itamark@...zon.com, shellykz@...zon.com, shorer@...zon.com,
        amitlavi@...zon.com, almogbs@...zon.com, dwmw@...zon.co.uk,
        rtanwar@...linear.com
Subject: Re: [PATCH v2 11/16] hwmon: (mr75203) add protection for negative
 voltage value

On Wed, Aug 17, 2022 at 05:43:16AM +0000, Eliav Farber wrote:
> This change makes sure the returned voltage vlaue is 0 or positive.
> 
> Signed-off-by: Eliav Farber <farbere@...zon.com>
> ---
>  drivers/hwmon/mr75203.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/hwmon/mr75203.c b/drivers/hwmon/mr75203.c
> index 24a00339cfd8..e3191f590167 100644
> --- a/drivers/hwmon/mr75203.c
> +++ b/drivers/hwmon/mr75203.c
> @@ -218,6 +218,13 @@ static int pvt_read_in(struct device *dev, u32 attr, int channel, long *val)
>  			return ret;
>  
>  		n &= SAMPLE_DATA_MSK;
> +
> +		/* Voltage can't be negative */

Who says, and what does that mean ? Under which conditions would
the value be negative, and why would that be a problem / bug ?
After all, negative voltages do exist.

Guenter

> +		if (PVT_N_CONST * n < PVT_R_CONST) {
> +			*val = 0;
> +			return 0;
> +		}
> +
>  		/* Convert the N bitstream count into voltage */
>  		*val = pvt->vd[channel].pre_scaler;
>  		*val *= (PVT_N_CONST * n - PVT_R_CONST);