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Diffstat (limited to 'Documentation/power/devices.txt')
| -rw-r--r-- | Documentation/power/devices.txt | 34 |
1 files changed, 30 insertions, 4 deletions
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt index 47d46df..d172bce 100644 --- a/Documentation/power/devices.txt +++ b/Documentation/power/devices.txt @@ -2,6 +2,7 @@ Device Power Management Copyright (c) 2010-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc. Copyright (c) 2010 Alan Stern <stern@rowland.harvard.edu> +Copyright (c) 2014 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com> Most of the code in Linux is device drivers, so most of the Linux power @@ -326,6 +327,20 @@ the phases are: driver in some way for the upcoming system power transition, but it should not put the device into a low-power state. + For devices supporting runtime power management, the return value of the + prepare callback can be used to indicate to the PM core that it may + safely leave the device in runtime suspend (if runtime-suspended + already), provided that all of the device's descendants are also left in + runtime suspend. Namely, if the prepare callback returns a positive + number and that happens for all of the descendants of the device too, + and all of them (including the device itself) are runtime-suspended, the + PM core will skip the suspend, suspend_late and suspend_noirq suspend + phases as well as the resume_noirq, resume_early and resume phases of + the following system resume for all of these devices. In that case, + the complete callback will be called directly after the prepare callback + and is entirely responsible for bringing the device back to the + functional state as appropriate. + 2. The suspend methods should quiesce the device to stop it from performing I/O. They also may save the device registers and put it into the appropriate low-power state, depending on the bus type the device is on, @@ -400,12 +415,23 @@ When resuming from freeze, standby or memory sleep, the phases are: the resume callbacks occur; it's not necessary to wait until the complete phase. + Moreover, if the preceding prepare callback returned a positive number, + the device may have been left in runtime suspend throughout the whole + system suspend and resume (the suspend, suspend_late, suspend_noirq + phases of system suspend and the resume_noirq, resume_early, resume + phases of system resume may have been skipped for it). In that case, + the complete callback is entirely responsible for bringing the device + back to the functional state after system suspend if necessary. [For + example, it may need to queue up a runtime resume request for the device + for this purpose.] To check if that is the case, the complete callback + can consult the device's power.direct_complete flag. Namely, if that + flag is set when the complete callback is being run, it has been called + directly after the preceding prepare and special action may be required + to make the device work correctly afterward. + At the end of these phases, drivers should be as functional as they were before suspending: I/O can be performed using DMA and IRQs, and the relevant clocks are -gated on. Even if the device was in a low-power state before the system sleep -because of runtime power management, afterwards it should be back in its -full-power state. There are multiple reasons why it's best to do this; they are -discussed in more detail in Documentation/power/runtime_pm.txt. +gated on. However, the details here may again be platform-specific. For example, some systems support multiple "run" states, and the mode in effect at |
