linux-kernel - Re: [PATCH] power: reset: ltc2952: fix float conversion error

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Date:   Tue, 7 Dec 2021 10:41:24 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Sebastian Reichel <sre@...nel.org>,
        René Moll <Rene.Moll@...ns.com>,
        Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] power: reset: ltc2952: fix float conversion error

On Sat, Dec 4, 2021 at 2:02 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> clang-14 does not like the way this driver converts a 'long double'
> to an integer when the target architecture disables floating point
> support:
>
> drivers/power/reset/ltc2952-poweroff.c:162:28: error: expression requires  'long double' type support, but target 'x86_64-unknown-linux' does not support it
>         data->wde_interval = 300L * 1E6L;
>                                   ^
>
> Turn this into pure integer math and make it more readable at the
> same time using the NSEC_PER_MSEC macro instead.
>
> Fixes: 6647156c00cc ("power: reset: add LTC2952 poweroff driver")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for the patch! The change in clang-14 (ToT) that triggered this
has had another patch on top reverting these diagnostics.
https://reviews.llvm.org/D114162

That said, this change is still worthwhile for the improved semantics, IMO.

Link: https://github.com/ClangBuiltLinux/linux/issues/1497
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  drivers/power/reset/ltc2952-poweroff.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/power/reset/ltc2952-poweroff.c b/drivers/power/reset/ltc2952-poweroff.c
> index fbb344353fe4..9fc88a9f244c 100644
> --- a/drivers/power/reset/ltc2952-poweroff.c
> +++ b/drivers/power/reset/ltc2952-poweroff.c
> @@ -159,8 +159,8 @@ static void ltc2952_poweroff_kill(void)
>
>  static void ltc2952_poweroff_default(struct ltc2952_poweroff *data)
>  {
> -       data->wde_interval = 300L * 1E6L;
> -       data->trigger_delay = ktime_set(2, 500L*1E6L);
> +       data->wde_interval = 300 * NSEC_PER_MSEC;
> +       data->trigger_delay = ktime_set(2, 500 * NSEC_PER_MSEC);
>
>         hrtimer_init(&data->timer_trigger, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
>         data->timer_trigger.function = ltc2952_poweroff_timer_trigger;
> --
> 2.29.2
>


-- 
Thanks,
~Nick Desaulniers