RE: [PATCH 1/2] PM / Domains: Support enter deepest state for multiple states domains

[Aisheng Dong <aisheng.dong@nxp.com>]

> From: Ulf Hansson [mailto:ulf.hansson@linaro.org]
> Sent: Wednesday, March 6, 2019 11:18 PM> 
> On Wed, 6 Mar 2019 at 14:35, Aisheng Dong <aisheng.dong@nxp.com>
> wrote:
> >
> > Currently the generic power domain will power off the domain if all
> > devices in it have been stopped during system suspend.
> >
> > It is done by checking if the domain is active in
> > genpd_sync_power_off, then disable it. However, for power domains
> > supporting multiple low power states, it may have already entered an
> > intermediate low power state by runtime PM before system suspend and
> > the status is already GPD_STATE_POWER_OFF which results in then the
> > power domain stay at an intermediate low power state during system
> suspend.
> > Then genpd_sync_power_off will keep it at the low power state instead
> > of completely gate off it.
> 
> I agree that this could be a concern. However, before we look for a solution, do
> you have practical use case where you observes this?
> 

Yes, this solution[1] is used by NXP internally for former releases that we have two
Level states for power Domains[2].
We use state 0 (Low Power Mode with state retention) for device runtime pm support
and state 1 (power off with no state retention) for system suspend resume case.

Without [1], we will meet the issue that all domains runtime suspended will stay at
low power mode instead of power off during system suspend which consumes more power.

1. https://source.codeaurora.org/external/imx/linux-imx/log/drivers/base/power?h=imx_4.14.78_1.0.0_ga
2. https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/soc/imx/pm-domains.c?h=imx_4.14.78_1.0.0_ga#n325

> >
> > Let's give the power domain a chance to switch to the deepest state in
> > case it's already off but in an intermediate low power state.
> >
> > Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
> > ---
> >  drivers/base/power/domain.c | 18 +++++++++++++++++-
> >  include/linux/pm_domain.h   |  1 +
> >  2 files changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> > index 61cd500..847a69e 100644
> > --- a/drivers/base/power/domain.c
> > +++ b/drivers/base/power/domain.c
> > @@ -959,7 +959,17 @@ static void genpd_sync_power_off(struct
> > generic_pm_domain *genpd, bool use_lock,  {
> >         struct gpd_link *link;
> >
> > -       if (!genpd_status_on(genpd) || genpd_is_always_on(genpd))
> > +       /*
> > +        * Give the power domain a chance to switch to the deepest state
> in
> > +        * case it's already off but in an intermediate low power state.
> > +        */
> > +       genpd->state_idx_saved = genpd->state_idx;
> > +
> > +       if (genpd_is_always_on(genpd))
> > +               return;
> > +
> > +       if (!genpd_status_on(genpd) &&
> > +           genpd->state_idx == (genpd->state_count - 1))
> >                 return;
> 
> This means that the ->power_off() callback may be called twice in a raw, for
> the genpd in question and in cases of multiple idle states.
> It could be a problem.
> 
> Well, currently it may not be a real issue, as I doubt there is rather few genpd
> backend drivers supporting multiple idle states, but still.
> 

So far, I've no idea what the problem could be as there's no multi states power domain
drivers in tree.

For IMX, there's no problem as the driver could handle it well.
The core code just provides an interface for driver to handle such requirement.

Do you know who else using such power domain with multi states?
I guess TI, but did not see their code in tree.

> >
> >         if (genpd->suspended_count != genpd->device_count) @@ -970,6
> > +980,9 @@ static void genpd_sync_power_off(struct generic_pm_domain
> *genpd, bool use_lock,
> >         if (_genpd_power_off(genpd, false))
> >                 return;
> >
> > +       if (genpd->status == GPD_STATE_POWER_OFF)
> > +               return;
> > +
> >         genpd->status = GPD_STATE_POWER_OFF;
> >
> >         list_for_each_entry(link, &genpd->slave_links, slave_node) {
> > @@ -1017,6 +1030,9 @@ static void genpd_sync_power_on(struct
> > generic_pm_domain *genpd, bool use_lock,
> >
> >         _genpd_power_on(genpd, false);
> >
> > +       /* restore save power domain state after resume */
> > +       genpd->state_idx = genpd->state_idx_saved;
> > +
> >         genpd->status = GPD_STATE_ACTIVE;  }
> >
> > diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> > index 1ed5874..95db21f 100644
> > --- a/include/linux/pm_domain.h
> > +++ b/include/linux/pm_domain.h
> > @@ -124,6 +124,7 @@ struct generic_pm_domain {
> >                 };
> >         };
> >
> > +       unsigned int state_idx_saved; /* saved power state for
> > + recovery after system suspend/resume */
> >  };
> >
> >  static inline struct generic_pm_domain *pd_to_genpd(struct
> > dev_pm_domain *pd)
> > --
> > 2.7.4
> >
> 
> I need to think about this a bit more, let me get back to you.
> 

Thanks for the help.

Regards
Dong Aisheng

> Kind regards
> Uffe