linux-kernel - RE: [PATCH v2 2/3] RFC: regulator: ad5398: Change selector division calculation

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Message-ID:
 <PH0PR03MB65127833FDCEA37075CBB3F68EEE2@PH0PR03MB6512.namprd03.prod.outlook.com>
Date: Wed, 29 Jan 2025 08:34:32 +0000
From: "Hennerich, Michael" <Michael.Hennerich@...log.com>
To: Isaac Scott <isaac.scott@...asonboard.com>
CC: "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "broonie@...nel.org"
	<broonie@...nel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 2/3] RFC: regulator: ad5398: Change selector division
 calculation



> -----Original Message-----
> From: Isaac Scott <isaac.scott@...asonboard.com>
> Sent: Tuesday, January 28, 2025 6:32 PM
> To: Hennerich, Michael <Michael.Hennerich@...log.com>
> Cc: lgirdwood@...il.com; broonie@...nel.org; linux-kernel@...r.kernel.org;
> Isaac Scott <isaac.scott@...asonboard.com>
> Subject: [PATCH v2 2/3] RFC: regulator: ad5398: Change selector division
> calculation
> 
> [External]
> 
> If the AD5398 is defined to have a current limit with no range, i.e.
> when max_Ua and min_Ua are equal, the DIV_ROUND_UP erroneously tries
> to set the current to a higher level than the max_Ua, which causes the driver to
> fail to set the current. Fix this so the driver slightly underestimates the current
> to set.
> 
> Signed-off-by: Isaac Scott <isaac.scott@...asonboard.com>
> ---
>  drivers/regulator/ad5398.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/regulator/ad5398.c b/drivers/regulator/ad5398.c index
> e6f45c6e750c..0c60ecd1f0f2 100644
> --- a/drivers/regulator/ad5398.c
> +++ b/drivers/regulator/ad5398.c
> @@ -98,8 +98,7 @@ static int ad5398_set_current_limit(struct regulator_dev
> *rdev, int min_uA, int
>  	if (min_uA > chip->max_uA || max_uA < chip->min_uA)
>  		return -EINVAL;
> 
> -	selector = DIV_ROUND_UP((min_uA - chip->min_uA) * chip-
> >current_level,
> -				range_uA);
> +	selector = ((min_uA - chip->min_uA) * chip->current_level /
> range_uA);

Not sure if this is a good idea. The rational was to set the limit slightly higher.
This will do the opposite. The ranges are already checked.
Why not clamp() the calculated value? 

>  	if (ad5398_calc_current(chip, selector) > max_uA)
>  		return -EINVAL;
> 
> --
> 2.43.0