On 22 June 2017 at 16:32, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > On Thursday, June 22, 2017 11:42:11 AM Ulf Hansson wrote: >> On 21 June 2017 at 23:47, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: >> > On Wed, Jun 21, 2017 at 9:21 PM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: >> >> This change extends the interpretation of the ACPI's no_direct_complete >> >> flag to be used to enable the so called runtime PM centric approach, for >> >> devices being attached to the ACPI PM domain. >> >> >> >> The principle behind the runtime PM centric approach is to re-use the >> >> runtime PM callbacks to implement system sleep for drivers/subsystems. >> >> Moreover, using the runtime PM centric approach gives an optimized >> >> behaviour around avoiding to wake up a device from its low power state >> >> during system sleep, unless really needed. >> >> >> >> To deploy the runtime PM centric approach for a subsystem/driver, the >> >> following adaptations needs to be made. >> >> >> >> First, the runtime PM callbacks may be called when runtime PM has been >> >> disabled for the device. This serves as an indication for the callbacks to >> >> understand they are running in the system sleep sequence, instead of in the >> >> regular runtime PM path. In some cases, a callback needs to take different >> >> actions depending in what path it is being executed in, as is the case for >> >> the ACPI PM domain. >> >> >> >> In particular for the ACPI PM domain's ->runtime_suspend|resume() >> >> callbacks, when those finds runtime PM being disabled for the device, it >> >> instead executes the same operations as normally being run when >> >> ->suspend_late() and ->resume_early() callbacks are invoked during system >> >> sleep. >> >> >> >> Second, at the PM domain level, it is expected that the driver for the >> >> device makes use of pm_runtime_force_suspend|resume(), to re-use the >> >> runtime PM callbacks to put the device into low power state and to wake it >> >> up when needed during system sleep. >> > >> > What if it doesn't do that? >> > >> > Do all drivers of devices that may fall into the ACPI PM domain use >> > pm_runtime_force_suspend|resume()? >> >> No, no - the runtime PM centric path is optional by all ACPI >> devices/drivers. The default is still for the ACPI PM domain to try >> the direct_complete path. >> >> However if an ACPI device/driver (i2c designware in this case) likes >> to do that, they need to inform the ACPI PM domain about it. Then they >> call acpi_dev_disable_direct_complete() and makes use of >> pm_runtime_force_suspend|resume() to deal with system sleep. >> >> Does that makes sense? > > Overall, yes, it does, but then it should be made clear that when you use > "no_direct_complete" (all what you are going to call that eventually), you > also must use pm_runtime_force_suspend|resume() as your sleep callbacks. Okay, so I will clarify that in the header of acpi_dev_disable_direct_complete() and I guess I should also update some documentation around ACPI. > > Otherwise things may not work correctly if my understanding is correct. Correct. Kind regards Uffe
