diff options
Diffstat (limited to 'Documentation/power')
| -rw-r--r-- | Documentation/power/pci.rst | 43 |
1 files changed, 22 insertions, 21 deletions
diff --git a/Documentation/power/pci.rst b/Documentation/power/pci.rst index f09b382b4621..1831e431f725 100644 --- a/Documentation/power/pci.rst +++ b/Documentation/power/pci.rst @@ -1010,32 +1010,33 @@ if the device is in runtime suspend when the system suspend starts. That also affects all of the ancestors of the device, so this flag should only be used if absolutely necessary. -The DPM_FLAG_SMART_PREPARE flag instructs the PCI bus type to only return a -positive value from pci_pm_prepare() if the ->prepare callback provided by the +The DPM_FLAG_SMART_PREPARE flag causes the PCI bus type to return a positive +value from pci_pm_prepare() only if the ->prepare callback provided by the driver of the device returns a positive value. That allows the driver to opt -out from using the direct-complete mechanism dynamically. +out from using the direct-complete mechanism dynamically (whereas setting +DPM_FLAG_NO_DIRECT_COMPLETE means permanent opt-out). The DPM_FLAG_SMART_SUSPEND flag tells the PCI bus type that from the driver's perspective the device can be safely left in runtime suspend during system suspend. That causes pci_pm_suspend(), pci_pm_freeze() and pci_pm_poweroff() -to skip resuming the device from runtime suspend unless there are PCI-specific -reasons for doing that. Also, it causes pci_pm_suspend_late/noirq(), -pci_pm_freeze_late/noirq() and pci_pm_poweroff_late/noirq() to return early -if the device remains in runtime suspend in the beginning of the "late" phase -of the system-wide transition under way. Moreover, if the device is in -runtime suspend in pci_pm_resume_noirq() or pci_pm_restore_noirq(), its runtime -power management status will be changed to "active" (as it is going to be put -into D0 going forward), but if it is in runtime suspend in pci_pm_thaw_noirq(), -the function will set the power.direct_complete flag for it (to make the PM core -skip the subsequent "thaw" callbacks for it) and return. - -Setting the DPM_FLAG_MAY_SKIP_RESUME flag means that the driver prefers the -device to be left in suspend after system-wide transitions to the working state. -This flag is checked by the PM core, but the PCI bus type informs the PM core -which devices may be left in suspend from its perspective (that happens during -the "noirq" phase of system-wide suspend and analogous transitions) and next it -uses the dev_pm_skip_resume() helper to decide whether or not to return from -pci_pm_resume_noirq() and pci_pm_resume_early() upfront. +to avoid resuming the device from runtime suspend unless there are PCI-specific +reasons for doing that. Also, it causes pci_pm_suspend_late/noirq() and +pci_pm_poweroff_late/noirq() to return early if the device remains in runtime +suspend during the "late" phase of the system-wide transition under way. +Moreover, if the device is in runtime suspend in pci_pm_resume_noirq() or +pci_pm_restore_noirq(), its runtime PM status will be changed to "active" (as it +is going to be put into D0 going forward). + +Setting the DPM_FLAG_MAY_SKIP_RESUME flag means that the driver allows its +"noirq" and "early" resume callbacks to be skipped if the device can be left +in suspend after a system-wide transition into the working state. This flag is +taken into consideration by the PM core along with the power.may_skip_resume +status bit of the device which is set by pci_pm_suspend_noirq() in certain +situations. If the PM core determines that the driver's "noirq" and "early" +resume callbacks should be skipped, the dev_pm_skip_resume() helper function +will return "true" and that will cause pci_pm_resume_noirq() and +pci_pm_resume_early() to return upfront without touching the device and +executing the driver callbacks. 3.2. Device Runtime Power Management ------------------------------------ |