linux-kernel - [PATCH] PM: Add comment describing relationships between PM callbacks to pm.h

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Message-Id: <201202130039.02184.rjw@sisk.pl>
Date:	Mon, 13 Feb 2012 00:39:02 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linux PM list <linux-pm@...r.kernel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Kevin Hilman <khilman@...com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Magnus Damm <magnus.damm@...il.com>
Subject: [PATCH] PM: Add comment describing relationships between PM callbacks to pm.h

From: Rafael J. Wysocki <rjw@...k.pl>

The UNIVERSAL_DEV_PM_OPS() macro is slightly misleading, because it
may suggest that it's a good idea to point runtime PM callback
pointers to the same routines as system suspend/resume callbacks
.suspend() and .resume(), which is not the case.  For this reason,
add a comment to include/linux/pm.h, next to the definition of
UNIVERSAL_DEV_PM_OPS(), describing how device PM callbacks are
related to each other.

Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
 include/linux/pm.h |    9 +++++++++
 1 file changed, 9 insertions(+)

Index: linux/include/linux/pm.h
===================================================================
--- linux.orig/include/linux/pm.h
+++ linux/include/linux/pm.h
@@ -320,6 +320,15 @@ const struct dev_pm_ops name = { \
 /*
  * Use this for defining a set of PM operations to be used in all situations
  * (sustem suspend, hibernation or runtime PM).
+ * NOTE: In general, system suspend callbacks, .suspend() and .resume(), should
+ * be different from the corresponding runtime PM callbacks, .runtime_suspend(),
+ * and .runtime_resume(), because .runtime_suspend() always works on an already
+ * quiescent device, while .suspend() should assume that the device may be doing
+ * something when it is called (it should ensure that the device will be
+ * quiescent after it has returned).  Therefore it's better to point the "late"
+ * suspend and "early" resume callback pointers, .suspend_late() and
+ * .resume_early(), to the same routines as .runtime_suspend() and
+ * .runtime_resume(), respectively (and analogously for hibernation).
  */
 #define UNIVERSAL_DEV_PM_OPS(name, suspend_fn, resume_fn, idle_fn) \
 const struct dev_pm_ops name = { \
--
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