linux-kernel - [PATCH 1/3] printk: Allow architecture-specific timestamping function

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Date:   Mon, 22 Jul 2019 11:33:28 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] printk: Allow architecture-specific timestamping function

printk currently relies on local_clock to time-stamp the kernel
messages. In order to allow the timestamping (and only that)
to be overridden by architecture-specific code, let's declare
a new timestamp_clock() function, which gets used by the printk
code. Architectures willing to make use of this facility will
have to define CONFIG_ARCH_HAS_TIMESTAMP_CLOCK.

The default is of course to return local_clock(), so that the
existing behaviour stays unchanged.

Signed-off-by: Marc Zyngier <marc.zyngier@....com>
---
 include/linux/sched/clock.h | 13 +++++++++++++
 kernel/printk/printk.c      |  4 ++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/clock.h b/include/linux/sched/clock.h
index 867d588314e0..3cf4b2a8ce18 100644
--- a/include/linux/sched/clock.h
+++ b/include/linux/sched/clock.h
@@ -98,4 +98,17 @@ static inline void enable_sched_clock_irqtime(void) {}
 static inline void disable_sched_clock_irqtime(void) {}
 #endif
 
+#ifdef CONFIG_ARCH_HAS_TIMESTAMP_CLOCK
+/* Special need architectures can provide their timestamping function */
+extern u64 timestamp_clock(void);
+
+#else
+
+static inline u64 timestamp_clock(void)
+{
+	return local_clock();
+}
+
+#endif
+
 #endif /* _LINUX_SCHED_CLOCK_H */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 1888f6a3b694..166702316714 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -638,7 +638,7 @@ static int log_store(u32 caller_id, int facility, int level,
 	if (ts_nsec > 0)
 		msg->ts_nsec = ts_nsec;
 	else
-		msg->ts_nsec = local_clock();
+		msg->ts_nsec = timestamp_clock();
 #ifdef CONFIG_PRINTK_CALLER
 	msg->caller_id = caller_id;
 #endif
@@ -1841,7 +1841,7 @@ static bool cont_add(u32 caller_id, int facility, int level,
 		cont.facility = facility;
 		cont.level = level;
 		cont.caller_id = caller_id;
-		cont.ts_nsec = local_clock();
+		cont.ts_nsec = timestamp_clock();
 		cont.flags = flags;
 	}
 
-- 
2.20.1