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

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Date:   Fri,  5 Nov 2021 08:20:50 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH v2] power: reset: ltc2952: Fix use of floating point literals

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>
---

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