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authorLinus Torvalds <torvalds@linux-foundation.org>2011-11-05 17:54:18 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-11-05 17:54:18 -0700
commit8110efc64c4790cd1bf7e30f080e5ba3faa7cb85 (patch)
tree708c2a1ef6bebce8eda9676c554bea366547678e /Documentation
parent06d8eb1b7d1eb34c76538dab791bc14136ebbc8f (diff)
parentd6cc76856d353a3a9c43bead33210b9216dce332 (diff)
downloadvexpress-lsk-8110efc64c4790cd1bf7e30f080e5ba3faa7cb85.tar.gz
Merge branch 'pm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
* 'pm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm: PM / Freezer: Revert 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK_KILLABLE tasks too" PM / Freezer: Reimplement wait_event_freezekillable using freezer_do_not_count/freezer_count USB: Update last_busy time after autosuspend fails PM / Runtime: Automatically retry failed autosuspends PM / QoS: Remove redundant check PM / OPP: Fix build when CONFIG_PM_OPP is not set PM / Runtime: Fix runtime accounting calculation error PM / Sleep: Update freezer documentation PM / Sleep: Remove unused symbol 'suspend_cpu_hotplug' PM / Sleep: Fix race between CPU hotplug and freezer ACPI / PM: Add Sony VPCEB17FX to nonvs blacklist
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/power/freezing-of-tasks.txt8
-rw-r--r--Documentation/power/runtime_pm.txt10
2 files changed, 14 insertions, 4 deletions
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt
index 38b57248fd6..316c2ba187f 100644
--- a/Documentation/power/freezing-of-tasks.txt
+++ b/Documentation/power/freezing-of-tasks.txt
@@ -22,12 +22,12 @@ try_to_freeze_tasks() that sets TIF_FREEZE for all of the freezable tasks and
either wakes them up, if they are kernel threads, or sends fake signals to them,
if they are user space processes. A task that has TIF_FREEZE set, should react
to it by calling the function called refrigerator() (defined in
-kernel/power/process.c), which sets the task's PF_FROZEN flag, changes its state
+kernel/freezer.c), which sets the task's PF_FROZEN flag, changes its state
to TASK_UNINTERRUPTIBLE and makes it loop until PF_FROZEN is cleared for it.
Then, we say that the task is 'frozen' and therefore the set of functions
handling this mechanism is referred to as 'the freezer' (these functions are
-defined in kernel/power/process.c and include/linux/freezer.h). User space
-processes are generally frozen before kernel threads.
+defined in kernel/power/process.c, kernel/freezer.c & include/linux/freezer.h).
+User space processes are generally frozen before kernel threads.
It is not recommended to call refrigerator() directly. Instead, it is
recommended to use the try_to_freeze() function (defined in
@@ -95,7 +95,7 @@ after the memory for the image has been freed, we don't want tasks to allocate
additional memory and we prevent them from doing that by freezing them earlier.
[Of course, this also means that device drivers should not allocate substantial
amounts of memory from their .suspend() callbacks before hibernation, but this
-is e separate issue.]
+is a separate issue.]
3. The third reason is to prevent user space processes and some kernel threads
from interfering with the suspending and resuming of devices. A user space
diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
index 0e856088db7..5336149f831 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.