Re: [RFC][PATCH 1/3] PM / sleep: Flag to speed up suspend-resume of runtime-suspended devices

[Ulf Hansson <ulf.hansson@linaro.org>]

On 8 May 2014 12:53, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> On Thursday, May 08, 2014 09:49:36 AM Ulf Hansson wrote:
>> On 8 May 2014 01:29, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>> >
>> > Currently, some subsystems (e.g. PCI and the ACPI PM domain) have to
>> > resume all runtime-suspended devices during system suspend, mostly
>> > because those devices may need to be reprogrammed due to different
>> > wakeup settings for system sleep and for runtime PM.
>> >
>> > For some devices, though, it's OK to remain in runtime suspend
>> > throughout a complete system suspend/resume cycle (if the device was in
>> > runtime suspend at the start of the cycle).  We would like to do this
>> > whenever possible, to avoid the overhead of extra power-up and power-down
>> > events.
>> >
>> > However, problems may arise because the device's descendants may require
>> > it to be at full power at various points during the cycle.  Therefore the
>> > most straightforward way to do this safely is if the device and all its
>> > descendants can remain runtime suspended until the resume stage of system
>> > resume.
>> >
>> > To this end, introduce dev->power.leave_runtime_suspended.
>> > If a subsystem or driver sets this flag during the ->prepare() callback,
>> > and if the flag is set in all of the device's descendants, and if the
>> > device is still in runtime suspend at the beginning of the ->suspend()
>> > callback, that callback is allowed to return 0 without clearing
>> > power.leave_runtime_suspended and without changing the state of the
>> > device, unless the current state of the device is not appropriate for
>> > the upcoming system sleep state (for example, the device is supposed to
>> > wake up the system from that state and its current wakeup settings are
>> > not suitable for that).  Then, the PM core will not invoke the device's
>> > ->suspend_late(), ->suspend_irq(), ->resume_irq(), ->resume_early(), or
>> > ->resume() callbacks.  Instead, it will invoke ->runtime_resume() during
>> > the device resume stage of system resume.
>> >
>> > By leaving this flag set after ->suspend(), a driver or subsystem tells
>> > the PM core that the device is runtime suspended, it is in a suitable
>> > state for system suspend (for example, the wakeup setting does not
>> > need to be changed), and it does not need to return to full
>> > power until the resume stage.
>> >
>> > Changelog based on an Alan Stern's description of the idea
>> > (http://marc.info/?l=linux-pm&m=139940466625569&w=2).
>> >
>> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>> > ---
>> >  drivers/base/power/main.c    |   31 ++++++++++++++++++++++++-------
>> >  drivers/base/power/runtime.c |   10 ++++++++++
>> >  include/linux/pm.h           |    3 +++
>> >  include/linux/pm_runtime.h   |   16 ++++++++++++++++
>> >  kernel/power/Kconfig         |    4 ++++
>> >  5 files changed, 57 insertions(+), 7 deletions(-)
>> >
>> > Index: linux-pm/kernel/power/Kconfig
>> > ===================================================================
>> > --- linux-pm.orig/kernel/power/Kconfig
>> > +++ linux-pm/kernel/power/Kconfig
>> > @@ -147,6 +147,10 @@ config PM
>> >         def_bool y
>> >         depends on PM_SLEEP || PM_RUNTIME
>> >
>> > +config PM_BOTH
>> > +       def_bool y
>> > +       depends on PM_SLEEP && PM_RUNTIME
>> > +
>>
>> Should we not depend on PM_RUNTIME only? Thus we don't need the new
>> Kconfig,
>
> Well, OK.  I guess we can tolerate one useless statement in rpm_resume()
> in case CONFIG_PM_SLEEP is unset.
>
>> and then we could rename the new APIs to pm_runtime_* instead.
>
> That would just make the name longer - for what value?

Only "__set_leave_runtime_suspended" will be a bit longer.

The idea I had was to clearly indicate, these functions is a part of
PM_RUNTIME API.

Compare what you have:
__set_leave_runtime_suspended
pm_set_leave_runtime_suspended
pm_leave_runtime_suspended

To what I suggest:
__pm_runtime_set_leave_suspended
pm_runtime_set_leave_suspended
pm_runtime_leave_suspended

Kind regards
Ulf Hansson