On Thu, Jun 22, 2017 at 11:14 PM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: > 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. I think it also would be good to make acpi_dev_disable_direct_complete() check the conditions and throw a stack dump if they are not met. >> >> Otherwise things may not work correctly if my understanding is correct. > > Correct. OK In that case the no_direct_complete flag should be set for the entire time the driver is bound to the device. Therefore (a) It should go into struct acpi_device_power_flags. (b) It should be set at the probe time and cleared at the remove time. Thanks, Rafael
