1 files changed, 10 insertions, 0 deletions

diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
index 0e856088db7c..5336149f831b 100644
--- a/Documentation/power/runtime_pm.txt
+++ b/Documentation/power/runtime_pm.txt
@@ -789,6 +789,16 @@ will behave normally, not taking the autosuspend delay into account.
 Similarly, if the power.use_autosuspend field isn't set then the autosuspend
 helper functions will behave just like the non-autosuspend counterparts.
 
+Under some circumstances a driver or subsystem may want to prevent a device
+from autosuspending immediately, even though the usage counter is zero and the
+autosuspend delay time has expired.  If the ->runtime_suspend() callback
+returns -EAGAIN or -EBUSY, and if the next autosuspend delay expiration time is
+in the future (as it normally would be if the callback invoked
+pm_runtime_mark_last_busy()), the PM core will automatically reschedule the
+autosuspend.  The ->runtime_suspend() callback can't do this rescheduling
+itself because no suspend requests of any kind are accepted while the device is
+suspending (i.e., while the callback is running).
+
 The implementation is well suited for asynchronous use in interrupt contexts.
 However such use inevitably involves races, because the PM core can't
 synchronize ->runtime_suspend() callbacks with the arrival of I/O requests.