linux-kernel - Re: [PATCH] hwmon:fam15h_power Use div64

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Message-ID: <20251230232357.00222b64@pumpkin>
Date: Tue, 30 Dec 2025 23:23:57 +0000
From: David Laight <david.laight.linux@...il.com>
To: SeungJu Cheon <suunj1331@...il.com>
Cc: ray.huang@....com, linux@...ck-us.net, linux-hwmon@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon:fam15h_power Use div64_u64() for 64-bit divisor

On Tue, 30 Dec 2025 21:09:59 +0900
SeungJu Cheon <suunj1331@...il.com> wrote:

> tdelta is u64, but do_div() truncates the divisor to 32 bits.
> Use div64_u64() to handle the full 64-bit divisor correctly.

Looking at the code I think that tdelta is a time interval and will
always fit in 32bits - so the code is probably fine.

Also I can't see anything that requires jdelta[] be an array.
Neither can I see the justification for MAX_CUS being 8.

> 
> Signed-off-by: SeungJu Cheon <suunj1331@...il.com>
> ---
>  drivers/hwmon/fam15h_power.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/fam15h_power.c b/drivers/hwmon/fam15h_power.c
> index 8ecebea53651..5e3692606516 100644
> --- a/drivers/hwmon/fam15h_power.c
> +++ b/drivers/hwmon/fam15h_power.c
> @@ -241,7 +241,7 @@ static ssize_t power1_average_show(struct device *dev,
>  		}
>  		tdelta = data->cpu_sw_pwr_ptsc[cu] - prev_ptsc[cu];
>  		jdelta[cu] *= data->cpu_pwr_sample_ratio * 1000;
> -		do_div(jdelta[cu], tdelta);
> +		jdelta[cu] = div64_u64(jdelta[cu], tdelta);
>  
>  		/* the unit is microWatt */
>  		avg_acc += jdelta[cu];

That could be:
		jdelta *= data->cpu_pwr_sample_ratio * 1000;
		avg_acc += div64_u64(jdelta, tdelta);
(or even 1 line...)

	David