[PATCH 1/9] PM / Domains: Add dev_pm_domain_get|put() APIs
Rafael J. Wysocki
rjw at rjwysocki.net
Tue Mar 17 07:45:55 PDT 2015
On Tuesday, March 17, 2015 10:27:03 AM Ulf Hansson wrote:
> On 17 March 2015 at 04:01, Rafael J. Wysocki <rjw at rjwysocki.net> wrote:
> > On Monday, March 16, 2015 10:26:46 AM Ulf Hansson wrote:
> >> On 14 March 2015 at 02:31, Rafael J. Wysocki <rjw at rjwysocki.net> wrote:
> >> > On Friday, March 13, 2015 04:43:41 PM Ulf Hansson wrote:
> >> >> There may be more than one device in a PM domain which then will be
> >> >> probed at different points in time.
> >> >>
> >> >> Depending on timing and runtime PM support, in for the device related
> >> >> driver/subsystem, a PM domain may be advised to power off after a
> >> >> successful probe sequence.
> >> >>
> >> >> A general requirement for a device within a PM domain, is that the
> >> >> PM domain must stay powered during the probe sequence. To cope with
> >> >> such requirement, let's add the dev_pm_domain_get|put() APIs.
> >> >>
> >> >> These APIs are intended to be invoked from subsystem-level code and the
> >> >> calls between get/put needs to be balanced.
> >> >>
> >> >> dev_pm_domain_get(), tells the PM domain that it needs to increase a
> >> >> usage count and to keep supplying power. dev_pm_domain_put(), does the
> >> >> opposite.
> >> >>
> >> >> For a PM domain to support this feature, it must implement the optional
> >> >> ->get|put() callbacks.
> >> >>
> >> >> Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>
> >> >> ---
> >> >> drivers/base/power/common.c | 40 ++++++++++++++++++++++++++++++++++++++++
> >> >> include/linux/pm.h | 2 ++
> >> >> include/linux/pm_domain.h | 4 ++++
> >> >> 3 files changed, 46 insertions(+)
> >> >>
> >> >> diff --git a/drivers/base/power/common.c b/drivers/base/power/common.c
> >> >> index f32b802..99225af 100644
> >> >> --- a/drivers/base/power/common.c
> >> >> +++ b/drivers/base/power/common.c
> >> >> @@ -128,3 +128,43 @@ void dev_pm_domain_detach(struct device *dev, bool power_off)
> >> >> dev->pm_domain->detach(dev, power_off);
> >> >> }
> >> >> EXPORT_SYMBOL_GPL(dev_pm_domain_detach);
> >> >> +
> >> >> +/**
> >> >> + * dev_pm_domain_get - Increase usage count to keep a PM domain powered.
> >> >> + * @domain: The PM domain to operate on.
> >> >> + *
> >> >> + * This function will not by itself increase the usage count, that's up to each
> >> >> + * PM domain implementation to support. Typically it should be invoked from
> >> >> + * subsystem level code prior drivers starts probing.
> >> >> + *
> >> >> + * Do note, it's optional to implement the ->get() callback for a PM domain.
> >> >> + *
> >> >> + * Returns 0 on successfully increased usage count or negative error code.
> >> >> + */
> >> >> +int dev_pm_domain_get(struct dev_pm_domain *domain)
> >> >> +{
> >> >> + int ret = 0;
> >> >> +
> >> >> + if (domain && domain->get)
> >> >> + ret = domain->get(domain);
> >> >> +
> >> >> + return ret;
> >> >> +}
> >> >> +EXPORT_SYMBOL_GPL(dev_pm_domain_get);
> >> >> +
> >> >> +/**
> >> >> + * dev_pm_domain_put - Decrease usage count to allow a PM domain to power off.
> >> >> + * @domain: The PM domain to operate on.
> >> >> + *
> >> >> + * This function will not by itself decrease the usage count, that's up to each
> >> >> + * PM domain implementation to support. Typically it should be invoked from
> >> >> + * subsystem level code after drivers has finished probing.
> >> >> + *
> >> >> + * Do note, it's optional to implement the ->put() callback for a PM domain.
> >> >> + */
> >> >> +void dev_pm_domain_put(struct dev_pm_domain *domain)
> >> >> +{
> >> >> + if (domain && domain->put)
> >> >> + domain->put(domain);
> >> >> +}
> >> >> +EXPORT_SYMBOL_GPL(dev_pm_domain_put);
> >> >> diff --git a/include/linux/pm.h b/include/linux/pm.h
> >> >> index e2f1be6..e62330b 100644
> >> >> --- a/include/linux/pm.h
> >> >> +++ b/include/linux/pm.h
> >> >> @@ -607,6 +607,8 @@ extern void dev_pm_put_subsys_data(struct device *dev);
> >> >> struct dev_pm_domain {
> >> >> struct dev_pm_ops ops;
> >> >> void (*detach)(struct device *dev, bool power_off);
> >> >> + int (*get)(struct dev_pm_domain *domain);
> >> >> + void (*put)(struct dev_pm_domain *domain);
> >> >
> >> > I don't like these names. They suggest that it's always going to be about
> >> > reference counting which doesn't have to be the case in principle.
> >>
> >> I am happy to change, you don't happen to have a proposal? :-)
> >>
> >> For genpd we already have these related APIs:
> >>
> >> pm_genpd_poweron()
> >> pm_genpd_name_poweron()
> >> pm_genpd_poweroff_unused()
> >>
> >> Theoretically we should be able to replace these with
> >> dev_pm_domain_get|put() or whatever we decide to name them to.
> >>
> >> >
> >> > Also what about calling these from the driver core, ie. really_probe()?
> >>
> >> I like that!
> >>
> >> That also implies moving the calls to dev_pm_domain_attach|detach()
> >> out of the buses and into the drivercore, since we need the PM domain
> >> to be attached before calling dev_pm_domain_get|put(). I assume that's
> >> what you also propose me to change, right?
> >
> > Not really. I don't want to inflict the ACPI PM domain on every bus type
> > that may not be prepared for using it or even may not want to use it (like
> > PCI or PNP). That applies to genpd too to some extent.
> >
> > So bus types need to be able to opt in for using "default" PM domains, but
> > at the same time if they do, the core is a better place to invoke the
> > callbacks.
>
> Okay!
>
> >
> > The patch below shows how that can be done. For the bus types using
> > genpd or the ACPI PM domain today ->pm_domain_init and ->pm_domain_exit
> > may point to the routines initializing/detaching those (which also will help
> > to reduce code duplication somewhat) and that guarantees that the domains
> > will be attached to devices before probing and the core can do the ->pre_probe
> > and ->post_probe things for everybody.
>
> Overall, this seem like a very good idea!
>
> >
> > Rafael
> >
> >
> > ---
> > drivers/base/bus.c | 12 +++++++++++-
> > drivers/base/dd.c | 9 +++++++++
> > include/linux/device.h | 3 +++
> > include/linux/pm.h | 2 ++
> > 4 files changed, 25 insertions(+), 1 deletion(-)
> >
> > Index: linux-pm/drivers/base/bus.c
> > ===================================================================
> > --- linux-pm.orig/drivers/base/bus.c
> > +++ linux-pm/drivers/base/bus.c
> > @@ -509,10 +509,15 @@ int bus_add_device(struct device *dev)
> > int error = 0;
> >
> > if (bus) {
> > + if (bus->pm_domain_init) {
> > + error = bus->pm_domain_init(dev);
> > + if (error)
> > + goto out_put;
> > + }
> > pr_debug("bus: '%s': add device %s\n", bus->name, dev_name(dev));
> > error = device_add_attrs(bus, dev);
> > if (error)
> > - goto out_put;
> > + goto out_pm_domain;
> > error = device_add_groups(dev, bus->dev_groups);
> > if (error)
> > goto out_groups;
> > @@ -534,6 +539,9 @@ out_groups:
> > device_remove_groups(dev, bus->dev_groups);
> > out_id:
> > device_remove_attrs(bus, dev);
> > +out_pm_domain:
> > + if (bus->pm_domain_exit)
> > + bus->pm_domain_exit(dev);
> > out_put:
> > bus_put(dev->bus);
> > return error;
>
> To make this work for bus_add_device(), we first need to change the
> registration procedure for genpd DT providers. Currently that's done
> when "PM domain drivers" invokes the __of_genpd_add_provider() API,
> from SoC specific code and from different init levels.
>
> We need to have the available gendp DT providers registered when the
> ->pm_domain_init() callback is invoked.
>
> Besides the changes above, genpd also needs to deal with attached
> devices, but which don't have a corresponding driver bound. I believe
> we have some corner cases to fix around this as well.
>
> As an intermediate step, how about adding the similar code as above
> but into really_probe()? For the code in bus_remove_device() below, we
> could add that into __device_release_driver()?
Well, I wouldn't really like to add new callbacks to struct bus_type for
intermediate steps, because that's guaranteed to lead to confusion.
So I think the infrastructure is better added first and users may be
switched over to it gradually.
I don't see any particular problems with moving the ACPI PM domain
attach/detach to bus_add/remove_device(), so that can be done as the first
step. As for genpd, it can implement the ->post_probe thing first and do
the rest in the bus type ->probe until the generic code is ready.
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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