Re: [RFC PATCH v2 1/2] PM: domains: Skip disabling unused domains if provider has sync_state

[Dmitry Baryshkov]

On 02/02/2023 20:24, Matthias Kaehlcke wrote:
> Hi Abel,
>
> On Fri, Jan 27, 2023 at 12:40:53PM +0200, Abel Vesa wrote:
> > Currently, there are cases when a domain needs to remain enabled until
> > the consumer driver probes. Sometimes such consumer drivers may be built
> > as modules. Since the genpd_power_off_unused is called too early for
> > such consumer driver modules to get a chance to probe, the domain, since
> > it is unused, will get disabled. On the other hand, the best time for
> > an unused domain to be disabled is on the provider's sync_state
> > callback. So, if the provider has registered a sync_state callback,
> > assume the unused domains for that provider will be disabled on its
> > sync_state callback. Also provide a generic sync_state callback which
> > disables all the domains unused for the provider that registers it.
> >
> > Signed-off-by: Abel Vesa <abel.vesa@xxxxxxxxxx>
> > ---
> >
> > This approach has been applied for unused clocks as well.
> > With this patch merged in, all the providers that have sync_state
> > callback registered will leave the domains enabled unless the provider's
> > sync_state callback explicitly disables them. So those providers will
> > need to add the disabling part to their sync_state callback. On the
> > other hand, the platforms that have cases where domains need to remain
> > enabled (even if unused) until the consumer driver probes, will be able,
> > with this patch in, to run without the pd_ignore_unused kernel argument,
> > which seems to be the case for most Qualcomm platforms, at this moment.
>
> I recently encountered a related issue on a Qualcomm platform with a
> v6.2-rc kernel, which includes 3a39049f88e4 ("soc: qcom: rpmhpd: Use
> highest corner until sync_state"). The issue involves a DT node with a
> rpmhpd, the DT node is enabled, however the corresponding device driver
> is not enabled in the kernel. In such a scenario the sync_state callback
> is never called, because the genpd consumer never probes. As a result
> the Always-on subsystem (AOSS) of the SoC doesn't enter sleep mode during
> system suspend, which results in a substantially higher power consumption
> in S3.
>
> I wonder if genpd (and some other frameworks) needs something like
> regulator_init_complete(), which turns off unused regulators 30s after
> system boot. That's conceptually similar to the current
> genpd_power_off_unused(), but would provide time for modules being loaded.

I think the overall goal is to move away from ad-hoc implementations 
like clk_disable_unused/genpd_power_off_unused/regulator_init_complete 
towards the sync_state.

So inherently one either has to provide drivers for all devices in 
question or disable unused devices in DT.

> > The v1 is here:
> > https://lore.kernel.org/all/20230126234013.3638425-1-abel.vesa@xxxxxxxxxx/
> >
> > Changes since v1:
> >   * added a generic sync state callback to be registered by providers in
> >     order to disable the unused domains on their sync state. Also
> >     mentioned this in the commit message.
> >
> >   drivers/base/power/domain.c | 17 ++++++++++++++++-
> >   include/linux/pm_domain.h   |  3 +++
> >   2 files changed, 19 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> > index 84662d338188..c2a5f77c01f3 100644
> > --- a/drivers/base/power/domain.c
> > +++ b/drivers/base/power/domain.c
> > @@ -1099,7 +1099,8 @@ static int __init genpd_power_off_unused(void)
> >   	mutex_lock(&gpd_list_lock);
> >   
> >   	list_for_each_entry(genpd, &gpd_list, gpd_list_node)
> > -		genpd_queue_power_off_work(genpd);
> > +		if (!dev_has_sync_state(genpd->provider->dev))
> > +			genpd_queue_power_off_work(genpd);
> >   
> >   	mutex_unlock(&gpd_list_lock);
> >   
> > @@ -1107,6 +1108,20 @@ static int __init genpd_power_off_unused(void)
> >   }
> >   late_initcall(genpd_power_off_unused);
> >   
> > +void genpd_power_off_unused_sync_state(struct device *dev)
> > +{
> > +	struct generic_pm_domain *genpd;
> > +
> > +	mutex_lock(&gpd_list_lock);
> > +
> > +	list_for_each_entry(genpd, &gpd_list, gpd_list_node)
> > +		if (genpd->provider->dev == dev)
> > +			genpd_queue_power_off_work(genpd);
> > +
> > +	mutex_unlock(&gpd_list_lock);
> > +}
> > +EXPORT_SYMBOL_GPL(genpd_power_off_unused_sync_state);
> > +
> >   #ifdef CONFIG_PM_SLEEP
> >   
> >   /**
> > diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> > index f776fb93eaa0..1fd5aa500c81 100644
> > --- a/include/linux/pm_domain.h
> > +++ b/include/linux/pm_domain.h
> > @@ -351,6 +351,7 @@ struct device *genpd_dev_pm_attach_by_id(struct device *dev,
> >   					 unsigned int index);
> >   struct device *genpd_dev_pm_attach_by_name(struct device *dev,
> >   					   const char *name);
> > +void genpd_power_off_unused_sync_state(struct device *dev);
> >   #else /* !CONFIG_PM_GENERIC_DOMAINS_OF */
> >   static inline int of_genpd_add_provider_simple(struct device_node *np,
> >   					struct generic_pm_domain *genpd)
> > @@ -419,6 +420,8 @@ struct generic_pm_domain *of_genpd_remove_last(struct device_node *np)
> >   {
> >   	return ERR_PTR(-EOPNOTSUPP);
> >   }
> > +
> > +static inline genpd_power_off_unused_sync_state(struct device *dev) {}
> >   #endif /* CONFIG_PM_GENERIC_DOMAINS_OF */
> >   
> >   #ifdef CONFIG_PM
> > --
> > 2.34.1

--
With best wishes
Dmitry