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Re: [PATCH v2] drivers: cpuidle: assign enter_freeze to same as enter callback function

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  Re: [PATCH v2] drivers: cpuidle: assign enter_freeze to same as enter  callback function Sudeep Holla <sudeep.holla@arm.com> - 2016-11-15 15:30 +0100
    Re: [PATCH v2] drivers: cpuidle: assign enter_freeze to same as enter callback function "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-11-24 02:10 +0100

#1522771 — Re: [PATCH v2] drivers: cpuidle: assign enter_freeze to same as enter callback function

Hi Rafael,

On 10/11/16 14:24, Sudeep Holla wrote:
> enter_freeze() callback is expected atleast to do the same as enter()
> but it has to guarantee that interrupts aren't enabled at any point
> in its execution, as the tick is frozen.
>
> CPUs execute ->enter_freeze with the local tick or entire timekeeping
> suspended, so it must not re-enable interrupts at any point (even
> temporarily) or attempt to change states of clock event devices.
>
> It will be called when the system goes to suspend-to-idle and will
> reduce power usage because CPUs won't be awaken for unnecessary IRQs
> (i.e. woken up only on IRQs from "wakeup sources")
>
> We can reuse the same code for both the enter() and enter_freeze()
> callbacks as along as they don't re-enable interrupts. Only "coupled"
> cpuidle mechanism enables interrupts and doing that with timekeeping
> suspended is generally not safe.
>
> Since this generic DT based idle driver doesn't support "coupled"
> states, it is safe to assume that the interrupts are not re-enabled.
>
> This patch assign enter_freeze to same as enter callback function which
> helps to save power without any intermittent spurious wakeups from
> suspend-to-idle.
>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> ---
>  drivers/cpuidle/dt_idle_states.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> v1->v2:
> 	- Dropped checking and using only states with CPUIDLE_FLAG_TIMER_STOP
> 	  enabled.
>

Can you pick up this patch directly if there are no concerns ?

-- 
Regards,
Sudeep

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#1528904 — Re: [PATCH v2] drivers: cpuidle: assign enter_freeze to same as enter callback function

On Tuesday, November 15, 2016 02:20:21 PM Sudeep Holla wrote:
> Hi Rafael,
> 
> On 10/11/16 14:24, Sudeep Holla wrote:
> > enter_freeze() callback is expected atleast to do the same as enter()
> > but it has to guarantee that interrupts aren't enabled at any point
> > in its execution, as the tick is frozen.
> >
> > CPUs execute ->enter_freeze with the local tick or entire timekeeping
> > suspended, so it must not re-enable interrupts at any point (even
> > temporarily) or attempt to change states of clock event devices.
> >
> > It will be called when the system goes to suspend-to-idle and will
> > reduce power usage because CPUs won't be awaken for unnecessary IRQs
> > (i.e. woken up only on IRQs from "wakeup sources")
> >
> > We can reuse the same code for both the enter() and enter_freeze()
> > callbacks as along as they don't re-enable interrupts. Only "coupled"
> > cpuidle mechanism enables interrupts and doing that with timekeeping
> > suspended is generally not safe.
> >
> > Since this generic DT based idle driver doesn't support "coupled"
> > states, it is safe to assume that the interrupts are not re-enabled.
> >
> > This patch assign enter_freeze to same as enter callback function which
> > helps to save power without any intermittent spurious wakeups from
> > suspend-to-idle.
> >
> > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> > ---
> >  drivers/cpuidle/dt_idle_states.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > v1->v2:
> > 	- Dropped checking and using only states with CPUIDLE_FLAG_TIMER_STOP
> > 	  enabled.
> >
> 
> Can you pick up this patch directly if there are no concerns ?

There were none, so it's been queued up for 4.10.

Thanks,
Rafael

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