linux-kernel - Re: [PATCH] powercap/drivers/dtpm: Fix __udivdi3 and __aeabi

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Date:   Mon, 4 Jan 2021 09:18:43 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        kernel test robot <lkp@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powercap/drivers/dtpm: Fix __udivdi3 and __aeabi_uldivmod
 unresolved symbols

Hi Daniel,

On Wed, Dec 30, 2020 at 4:39 PM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
> 32 bits architectures do not support u64 division, so the macro
> DIV_ROUND_CLOSEST is not adequate as the compiler will replace the
> call to an unexisting function for the platform, leading to an
> unresolved symbols.
>
> Fix this by using the compatible macros:
>
> DIV64_U64_ROUND_CLOSEST and DIV_ROUND_CLOSEST_ULL.
>
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>

Thanks for your patch!

> --- a/drivers/powercap/dtpm.c
> +++ b/drivers/powercap/dtpm.c
> @@ -99,8 +99,8 @@ static void __dtpm_rebalance_weight(struct dtpm *dtpm)
>                 pr_debug("Setting weight '%d' for '%s'\n",
>                          child->weight, child->zone.name);
>
> -               child->weight = DIV_ROUND_CLOSEST(child->power_max * 1024,
> -                                                 dtpm->power_max);
> +               child->weight = DIV64_U64_ROUND_CLOSEST(
> +                       child->power_max * 1024, dtpm->power_max);

Note that 64-by-64 divisions are expensive on 32-bit platforms.

Does dtpm.power_max need to be u64?
The (lack of) documentation for the dtpm structure does not say what is
being stored there.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds