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notifiers.txt

notifiers.txt 2.7 KB
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  1. Suspend notifiers
    2. 

  2. 	(C) 2007 Rafael J. Wysocki <rjw@sisk.pl>, GPL
    3. 

  3. 

  4. There are some operations that device drivers may want to carry out in their
    5. 

  5. .suspend() routines, but shouldn't, because they can cause the hibernation or
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  6. suspend to fail. For example, a driver may want to allocate a substantial amount
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  7. of memory (like 50 MB) in .suspend(), but that shouldn't be done after the
    8. 

  8. swsusp's memory shrinker has run.
    9. 

  9. 

  10. Also, there may be some operations, that subsystems want to carry out before a
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  11. hibernation/suspend or after a restore/resume, requiring the system to be fully
    12. 

  12. functional, so the drivers' .suspend() and .resume() routines are not suitable
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  13. for this purpose.  For example, device drivers may want to upload firmware to
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  14. their devices after a restore from a hibernation image, but they cannot do it by
    15. 

  15. calling request_firmware() from their .resume() routines (user land processes
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  16. are frozen at this point).  The solution may be to load the firmware into
    17. 

  17. memory before processes are frozen and upload it from there in the .resume()
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  18. routine.  Of course, a hibernation notifier may be used for this purpose.
    19. 

  19. 

  20. The subsystems that have such needs can register suspend notifiers that will be
    21. 

  21. called upon the following events by the suspend core:
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  22. 

  23. PM_HIBERNATION_PREPARE	The system is going to hibernate or suspend, tasks will
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  24. 			be frozen immediately.
    25. 

  25. 

  26. PM_POST_HIBERNATION	The system memory state has been restored from a
    27. 

  27. 			hibernation image or an error occured during the
    28. 

  28. 			hibernation.  Device drivers' .resume() callbacks have
    29. 

  29. 			been executed and tasks have been thawed.
    30. 

  30. 

  31. PM_SUSPEND_PREPARE	The system is preparing for a suspend.
    32. 

  32. 

  33. PM_POST_SUSPEND		The system has just resumed or an error occured during
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  34. 			the suspend.	Device drivers' .resume() callbacks have
    35. 

  35. 			been executed and tasks have been thawed.
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  36. 

  37. It is generally assumed that whatever the notifiers do for
    38. 

  38. PM_HIBERNATION_PREPARE, should be undone for PM_POST_HIBERNATION.  Analogously,
    39. 

  39. operations performed for PM_SUSPEND_PREPARE should be reversed for
    40. 

  40. PM_POST_SUSPEND.  Additionally, all of the notifiers are called for
    41. 

  41. PM_POST_HIBERNATION if one of them fails for PM_HIBERNATION_PREPARE, and
    42. 

  42. all of the notifiers are called for PM_POST_SUSPEND if one of them fails for
    43. 

  43. PM_SUSPEND_PREPARE.
    44. 

  44. 

  45. The hibernation and suspend notifiers are called with pm_mutex held.  They are
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  46. defined in the usual way, but their last argument is meaningless (it is always
    47. 

  47. NULL).  To register and/or unregister a suspend notifier use the functions
    48. 

  48. register_pm_notifier() and unregister_pm_notifier(), respectively, defined in
    49. 

  49. include/linux/suspend.h .  If you don't need to unregister the notifier, you can
    50. 

  50. also use the pm_notifier() macro defined in include/linux/suspend.h .
    51.