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 13:44, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> On Thursday, May 08, 2014 12:59:20 PM Ulf Hansson wrote:
>> 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
>
> And why exactly do you think these are any better?

Because that's how all (almost all) other functions in the runtime PM
API are specified - I believe it makes sense to keep them aligned.

Anyway, if you insist in keeping your functions names, it's not that
of a big deal for me.

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

>
> The flag is not called leave_suspended surely?

To me that doesn't matter, the flag has nothing to do with the
function names in an API.

>
>
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.