diff options
Diffstat (limited to 'Documentation/power')
| -rw-r--r-- | Documentation/power/freezing-of-tasks.txt | 8 | ||||
| -rw-r--r-- | Documentation/power/notifiers.txt | 50 |
2 files changed, 55 insertions, 3 deletions
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt index af1a282c71a3..04dc1cf9d215 100644 --- a/Documentation/power/freezing-of-tasks.txt +++ b/Documentation/power/freezing-of-tasks.txt @@ -155,6 +155,8 @@ Suppose, however, that the firmware file is located on a filesystem accessible only through another device that hasn't been resumed yet. In that case, request_firmware() will fail regardless of whether or not the freezing of tasks is used. Consequently, the problem is not really related to the freezing of -tasks, since it generally exists anyway. [The solution to this particular -problem is to keep the firmware in memory after it's loaded for the first time -and upload if from memory to the device whenever necessary.] +tasks, since it generally exists anyway. + +A driver must have all firmwares it may need in RAM before suspend() is called. +If keeping them is not practical, for example due to their size, they must be +requested early enough using the suspend notifier API described in notifiers.txt. diff --git a/Documentation/power/notifiers.txt b/Documentation/power/notifiers.txt new file mode 100644 index 000000000000..9293e4bc857c --- /dev/null +++ b/Documentation/power/notifiers.txt @@ -0,0 +1,50 @@ +Suspend notifiers + (C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL + +There are some operations that device drivers may want to carry out in their +.suspend() routines, but shouldn't, because they can cause the hibernation or +suspend to fail. For example, a driver may want to allocate a substantial amount +of memory (like 50 MB) in .suspend(), but that shouldn't be done after the +swsusp's memory shrinker has run. + +Also, there may be some operations, that subsystems want to carry out before a +hibernation/suspend or after a restore/resume, requiring the system to be fully +functional, so the drivers' .suspend() and .resume() routines are not suitable +for this purpose. For example, device drivers may want to upload firmware to +their devices after a restore from a hibernation image, but they cannot do it by +calling request_firmware() from their .resume() routines (user land processes +are frozen at this point). The solution may be to load the firmware into +memory before processes are frozen and upload it from there in the .resume() +routine. Of course, a hibernation notifier may be used for this purpose. + +The subsystems that have such needs can register suspend notifiers that will be +called upon the following events by the suspend core: + +PM_HIBERNATION_PREPARE The system is going to hibernate or suspend, tasks will + be frozen immediately. + +PM_POST_HIBERNATION The system memory state has been restored from a + hibernation image or an error occured during the + hibernation. Device drivers' .resume() callbacks have + been executed and tasks have been thawed. + +PM_SUSPEND_PREPARE The system is preparing for a suspend. + +PM_POST_SUSPEND The system has just resumed or an error occured during + the suspend. Device drivers' .resume() callbacks have + been executed and tasks have been thawed. + +It is generally assumed that whatever the notifiers do for +PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION. Analogously, +operations performed for PM_SUSPEND_PREPARE should be reversed for +PM_POST_SUSPEND. Additionally, all of the notifiers are called for +PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and +all of the notifiers are called for PM_POST_SUSPEND if one of them fails for +PM_SUSPEND_PREPARE. + +The hibernation and suspend notifiers are called with pm_mutex held. They are +defined in the usual way, but their last argument is meaningless (it is always +NULL). To register and/or unregister a suspend notifier use the functions +register_pm_notifier() and unregister_pm_notifier(), respectively, defined in +include/linux/suspend.h . If you don't need to unregister the notifier, you can +also use the pm_notifier() macro defined in include/linux/suspend.h . |