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-rw-r--r--Documentation/power/runtime_pm.rst15
1 files changed, 14 insertions, 1 deletions
diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst
index 18ae21bf7f92..d6bf84f061f4 100644
--- a/Documentation/power/runtime_pm.rst
+++ b/Documentation/power/runtime_pm.rst
@@ -378,7 +378,11 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
`int pm_runtime_get_sync(struct device *dev);`
- increment the device's usage counter, run pm_runtime_resume(dev) and
- return its result
+ return its result;
+ note that it does not drop the device's usage counter on errors, so
+ consider using pm_runtime_resume_and_get() instead of it, especially
+ if its return value is checked by the caller, as this is likely to
+ result in cleaner code.
`int pm_runtime_get_if_in_use(struct device *dev);`
- return -EINVAL if 'power.disable_depth' is nonzero; otherwise, if the
@@ -827,6 +831,15 @@ or driver about runtime power changes. Instead, the driver for the device's
parent must take responsibility for telling the device's driver when the
parent's power state changes.
+Note that, in some cases it may not be desirable for subsystems/drivers to call
+pm_runtime_no_callbacks() for their devices. This could be because a subset of
+the runtime PM callbacks needs to be implemented, a platform dependent PM
+domain could get attached to the device or that the device is power managed
+through a supplier device link. For these reasons and to avoid boilerplate code
+in subsystems/drivers, the PM core allows runtime PM callbacks to be
+unassigned. More precisely, if a callback pointer is NULL, the PM core will act
+as though there was a callback and it returned 0.
+
9. Autosuspend, or automatically-delayed suspends
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