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? Kind regards Uffe
