linux-kernel - [PATCH v2 3/3] time: clocksource: Add a comment to CLOCK_SOURCE_SUSPEND

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Date:	Thu, 22 Jan 2015 12:01:17 +0000
From:	Xunlei Pang <pang.xunlei@...aro.org>
To:	linux-kernel@...r.kernel.org
Cc:	rtc-linux@...glegroups.com, Thomas Gleixner <tglx@...utronix.de>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	John Stultz <john.stultz@...aro.org>,
	Arnd Bergmann <arnd.bergmann@...aro.org>,
	Xunlei Pang <pang.xunlei@...aro.org>
Subject: [PATCH v2 3/3] time: clocksource: Add a comment to CLOCK_SOURCE_SUSPEND_NONSTOP

When doing timekeeping_resume(), if the nonstop clocksource
wraps back, "cycle_delta" will miss the wrap time.

It's hard to determine the right CLOCKSOURCE_MASK(xxx) or
something to add code for inspecting such behavior, and we
don't have many existent nonstop clocksources, so just add
a comment to indicate that if have this flag set, people
are aware that this nonstop clocksource won't wrap back
during system suspend/resume.

Signed-off-by: Xunlei Pang <pang.xunlei@...aro.org>
---
 include/linux/clocksource.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index abcafaa..8680189 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -207,6 +207,11 @@ struct clocksource {
 #define CLOCK_SOURCE_WATCHDOG			0x10
 #define CLOCK_SOURCE_VALID_FOR_HRES		0x20
 #define CLOCK_SOURCE_UNSTABLE			0x40
+
+/*
+ * When setting this flag, you're also supposed to mean that it doesn't
+ * wrap back during system suspend/resume. See timekeeping_resume().
+ */
 #define CLOCK_SOURCE_SUSPEND_NONSTOP		0x80
 #define CLOCK_SOURCE_RESELECT			0x100
 
-- 
1.9.1

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