linux-kernel - Re: [PATCH v2] power: reset: ltc2952: Fix use of floating point literals

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Message-ID: <20211116142614.ofqoox6zpn5erlc3@earth.universe>
Date:   Tue, 16 Nov 2021 15:26:14 +0100
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v2] power: reset: ltc2952: Fix use of floating point
 literals

Hi,

On Fri, Nov 05, 2021 at 08:20:50AM -0700, Nathan Chancellor 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 NSEC_PER_MSEC, 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>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---

Thanks, queued to power-supply's fixes branch.

-- Sebastian

> 
> v1 -> v2: https://lore.kernel.org/r/20211104215047.663411-1-nathan@kernel.org/
> 
> * A separate review pointed out that NSEC_PER_MSEC is a better choice
>   than USEC_PER_SEC because ktime_t is nanoseconds and the few functions
>   that take these values work in nanoseconds. The value is the same but
>   the documentation is better.
> 
> * Pick up Nick's review tag.
> 
>  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..65d9528cc989 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 * NSEC_PER_MSEC;
> +	data->trigger_delay = ktime_set(2, 500L * NSEC_PER_MSEC);
>  
>  	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
> 

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