linux-kernel - Re: [PATCH v2 2/4] docs: hwmon: (ltc2945): change type of val to ULL in ltc2945_val_to

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Date:   Wed, 11 Nov 2020 06:54:03 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     robh+dt@...nel.org, jdelvare@...e.com, mark.thoren@...log.com,
        ardeleanalex@...il.com
Subject: Re: [PATCH v2 2/4] docs: hwmon: (ltc2945): change type of val to ULL
 in ltc2945_val_to_reg()

On 11/11/20 1:12 AM, Alexandru Ardelean wrote:
> In order to account for any potential overflows that could occur.
> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>

Thinking about it, this can only really happen if the user provides
excessive values for limit attributes. Those are currently clamped
later, after the conversion. I think it would be better to modify
the code to apply a clamp _before_ the conversion as well instead
of trying to solve the overflow problem with unsigned long long.

Either case, can you send me a register dump for this chip ?
I'd like to write a module test script to actually check if there
are any over/underflows or other problems.

Thanks,
Guenter

> ---
>  drivers/hwmon/ltc2945.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c
> index 1cea710df668..6d4569a25471 100644
> --- a/drivers/hwmon/ltc2945.c
> +++ b/drivers/hwmon/ltc2945.c
> @@ -155,7 +155,7 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
>  }
>  
>  static int ltc2945_val_to_reg(struct device *dev, u8 reg,
> -			      unsigned long val)
> +			      unsigned long long val)
>  {
>  	struct ltc2945_state *st = dev_get_drvdata(dev);
>  	struct regmap *regmap = st->regmap;
> @@ -181,14 +181,14 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
>  			return ret;
>  		if (control & CONTROL_MULT_SELECT) {
>  			/* 25 mV * 25 uV = 0.625 uV resolution. */
> -			val = DIV_ROUND_CLOSEST(val, 625);
> +			val = DIV_ROUND_CLOSEST_ULL(val, 625);
>  		} else {
>  			/*
>  			 * 0.5 mV * 25 uV = 0.0125 uV resolution.
>  			 * Divide first to avoid overflow;
>  			 * accept loss of accuracy.
>  			 */
> -			val = DIV_ROUND_CLOSEST(val, 25) * 2;
> +			val = DIV_ROUND_CLOSEST_ULL(val, 25) * 2;
>  		}
>  		break;
>  	case LTC2945_VIN_H:
> @@ -197,7 +197,7 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
>  	case LTC2945_MAX_VIN_THRES_H:
>  	case LTC2945_MIN_VIN_THRES_H:
>  		/* 25 mV resolution. */
> -		val /= 25;
> +		val = div_u64(val, 25);
>  		break;
>  	case LTC2945_ADIN_H:
>  	case LTC2945_MAX_ADIN_H:
> @@ -219,7 +219,7 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
>  		 * dividing the reported current by the sense resistor value
>  		 * in mOhm.
>  		 */
> -		val = DIV_ROUND_CLOSEST(val, 25);
> +		val = DIV_ROUND_CLOSEST_ULL(val, 25);
>  		break;
>  	default:
>  		return -EINVAL;
> @@ -247,7 +247,7 @@ static ssize_t ltc2945_value_store(struct device *dev,
>  	struct ltc2945_state *st = dev_get_drvdata(dev);
>  	struct regmap *regmap = st->regmap;
>  	u8 reg = attr->index;
> -	unsigned long val;
> +	unsigned long long val;
>  	u8 regbuf[3];
>  	int num_regs;
>  	int regval;
>