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

[Rafael J. Wysocki]

On Thursday, May 08, 2014 02:25:06 PM Ulf Hansson wrote:
> On 8 May 2014 13:44, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> > On Thursday, May 08, 2014 12:59:20 PM Ulf Hansson wrote:
> >> On 8 May 2014 12:53, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> >> > On Thursday, May 08, 2014 09:49:36 AM Ulf Hansson wrote:
> >> >> On 8 May 2014 01:29, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
> >> >> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >> >> >
> >> >> > 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@xxxxxxxxx>
> >> >> > ---
> >> >> >  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@xxxxxxxxxx>
> 
> >
> > 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.

Well, the point is that pm_runtime_leave_suspended suggests that the runtime
PM framework is supposed to leave the device suspended, while this isn't the
case.  This essentially is a system suspend flag that depends on runtime PM
being available.

Thanks!


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