linux-kernel - Re: [PATCH] power: reset: ltc2952: Fix use of floating point literals

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Message-ID: <CAKwvOdkkKse-EkKMgBBx83eKeG6iXJVhusVRfhrQTrbOrwMtKA@mail.gmail.com>
Date:   Thu, 4 Nov 2021 14:54:28 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Sebastian Reichel <sre@...nel.org>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] power: reset: ltc2952: Fix use of floating point literals

On Thu, Nov 4, 2021 at 2:51 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> A new commit in LLVM causes an error on the use of 'long double' when
> '-mno-x87' is used, which the kernel does through an alias,
> '-mno-80387' (see the LLVM commit below for more details around why it
> does this).
>
> drivers/power/reset/ltc2952-poweroff.c:162:28: error: expression requires  'long double' type support, but target 'x86_64-unknown-linux-gnu' does not support it
>         data->wde_interval = 300L * 1E6L;
>                                   ^
> drivers/power/reset/ltc2952-poweroff.c:162:21: error: expression requires  'long double' type support, but target 'x86_64-unknown-linux-gnu' does not support it
>         data->wde_interval = 300L * 1E6L;
>                            ^
> drivers/power/reset/ltc2952-poweroff.c:163:41: error: expression requires  'long double' type support, but target 'x86_64-unknown-linux-gnu' does not support it
>         data->trigger_delay = ktime_set(2, 500L*1E6L);
>                                                ^
> 3 errors generated.
>
> This happens due to the use of a 'long double' literal. The 'E6' part of
> '1E6L' causes the literal to be a 'double' then the 'L' suffix promotes
> it to 'long double'.
>
> There is no visible reason for floating point values in this driver, as
> the values are only assigned to integer types. Use USEC_PER_SEC, which
> is the same integer value as '1E6L', to avoid changing functionality but
> fix the error.
>
> Fixes: 6647156c00cc ("power: reset: add LTC2952 poweroff driver")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1497
> Link: https://github.com/llvm/llvm-project/commit/a8083d42b1c346e21623a1d36d1f0cadd7801d83
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Thanks for the patch!
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..ebe3f2bed4c5 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 = 300L * USEC_PER_SEC;
> +       data->trigger_delay = ktime_set(2, 500L * USEC_PER_SEC);
>
>         hrtimer_init(&data->timer_trigger, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
>         data->timer_trigger.function = ltc2952_poweroff_timer_trigger;
>
> base-commit: d4439a1189f93d0ac1eaf0197db8e6b3e197d5c7
> --
> 2.34.0.rc0
>


-- 
Thanks,
~Nick Desaulniers