linux-kernel - [PATCH] time/sched_clock: Allow architecture to override cyc_to

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Message-Id: <20211114074704.3508622-1-chenhuacai@loongson.cn>
Date:   Sun, 14 Nov 2021 15:47:04 +0800
From:   Huacai Chen <chenhuacai@...ngson.cn>
To:     John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>,
        Huacai Chen <chenhuacai@...il.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Huacai Chen <chenhuacai@...ngson.cn>
Subject: [PATCH] time/sched_clock: Allow architecture to override cyc_to_ns()

The current cyc_to_ns() implementation is like this:

static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
{
	return (cyc * mult) >> shift;
}

But u64*u32 maybe overflow, so introduce ARCH_HAS_CYC_TO_NS to allow
architecture to override it.

Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
---
 kernel/time/Kconfig       | 4 ++++
 kernel/time/sched_clock.c | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 04bfd62f5e5c..5093e67115e8 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -30,6 +30,10 @@ config GENERIC_TIME_VSYSCALL
 config GENERIC_CLOCKEVENTS
 	def_bool !LEGACY_TIMER_TICK
 
+# Architecture has its own cyc_to_ns() implementation
+config ARCH_HAS_CYC_TO_NS
+	bool
+
 # Architecture can handle broadcast in a driver-agnostic way
 config ARCH_HAS_TICK_BROADCAST
 	bool
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index b1b9b12899f5..4496962e8e9f 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -63,10 +63,12 @@ static struct clock_data cd ____cacheline_aligned = {
 	.actual_read_sched_clock = jiffy_sched_clock_read,
 };
 
+#ifndef CONFIG_ARCH_HAS_CYC_TO_NS
 static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
 {
 	return (cyc * mult) >> shift;
 }
+#endif
 
 notrace struct clock_read_data *sched_clock_read_begin(unsigned int *seq)
 {
-- 
2.27.0