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Subject[PATCH] PM: Add comment describing relationships between PM callbacks to pm.h
Date
From: Rafael J. Wysocki <rjw@sisk.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@sisk.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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