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Date:	Thu, 19 Jun 2014 10:08:26 -0700
From:	Doug Anderson <>
To:	Daniel Lezcano <>,
	Kukjin Kim <>,
	Tomasz Figa <>
Cc:	Vincent Guittot <>,
	Chirantan Ekbote <>,
	David Riley <>,,,
	Amit Daniel Kachhap <>,,
	Doug Anderson <>,,,
Subject: [PATCH v2] clocksource: exynos_mct: Fix ftrace

In (93bfb76 clocksource: exynos_mct: register sched_clock callback) we
supported using the MCT as a scheduler clock.  We properly marked
exynos4_read_sched_clock() as notrace.  However, we then went and
called another function that _wasn't_ notrace.  That means if you do:

  cd /sys/kernel/debug/tracing/
  echo function_graph > current_tracer

You'll get a crash.

Fix this (but still let other readers of the MCT be trace-enabled) by
adding an extra function.  It's important to keep other users of MCT
traceable because the MCT is actually quite slow to access and we want
exynos4_frc_read() to show up in ftrace profiles if it's the

Signed-off-by: Doug Anderson <>
Changes in v2:
- Split out from other patches so this can go into 3.16.
- Better comment about why exynos4_frc_read() should be traceable.
- No more useless inline.

 drivers/clocksource/exynos_mct.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
index f71d55f..5ce99c0 100644
--- a/drivers/clocksource/exynos_mct.c
+++ b/drivers/clocksource/exynos_mct.c
@@ -162,7 +162,7 @@ static void exynos4_mct_frc_start(void)
 	exynos4_mct_write(reg, EXYNOS4_MCT_G_TCON);
-static cycle_t exynos4_frc_read(struct clocksource *cs)
+static cycle_t notrace _exynos4_frc_read(void)
 	unsigned int lo, hi;
 	u32 hi2 = __raw_readl(reg_base + EXYNOS4_MCT_G_CNT_U);
@@ -176,6 +176,11 @@ static cycle_t exynos4_frc_read(struct clocksource *cs)
 	return ((cycle_t)hi << 32) | lo;
+static cycle_t exynos4_frc_read(struct clocksource *cs)
+	return _exynos4_frc_read();
 static void exynos4_frc_resume(struct clocksource *cs)
@@ -192,7 +197,7 @@ struct clocksource mct_frc = {
 static u64 notrace exynos4_read_sched_clock(void)
-	return exynos4_frc_read(&mct_frc);
+	return _exynos4_frc_read();
 static void __init exynos4_clocksource_init(void)

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