linux-kernel - Re: [PATCH v3 1/2] PM: domains: Add devres variant for dev_pm_domain

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Message-ID: <CAJZ5v0hSqLGF_7xmiEf-=0gvHcNJjAsu-X60v6i3csv6ibc40g@mail.gmail.com>
Date: Sat, 7 Jun 2025 13:43:28 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>, Claudiu <claudiu.beznea@...on.dev>
Cc: gregkh@...uxfoundation.org, dakr@...nel.org, len.brown@...el.com, 
	pavel@...nel.org, ulf.hansson@...aro.org, jic23@...nel.org, 
	daniel.lezcano@...aro.org, linux-kernel@...r.kernel.org, 
	linux-pm@...r.kernel.org, bhelgaas@...gle.com, geert@...ux-m68k.org, 
	linux-iio@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	fabrizio.castro.jz@...esas.com, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH v3 1/2] PM: domains: Add devres variant for dev_pm_domain_attach()

On Fri, Jun 6, 2025 at 10:01 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Fri, Jun 6, 2025 at 8:55 PM Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
> >
> > On Fri, Jun 06, 2025 at 06:00:34PM +0200, Rafael J. Wysocki wrote:
> > > On Fri, Jun 6, 2025 at 1:18 PM Claudiu <claudiu.beznea@...on.dev> wrote:
> > > >
> > > > From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> > > >
> > > > The dev_pm_domain_attach() function is typically used in bus code alongside
> > > > dev_pm_domain_detach(), often following patterns like:
> > > >
> > > > static int bus_probe(struct device *_dev)
> > > > {
> > > >     struct bus_driver *drv = to_bus_driver(dev->driver);
> > > >     struct bus_device *dev = to_bus_device(_dev);
> > > >     int ret;
> > > >
> > > >     // ...
> > > >
> > > >     ret = dev_pm_domain_attach(_dev, true);
> > > >     if (ret)
> > > >         return ret;
> > > >
> > > >     if (drv->probe)
> > > >         ret = drv->probe(dev);
> > > >
> > > >     // ...
> > > > }
> > > >
> > > > static void bus_remove(struct device *_dev)
> > > > {
> > > >     struct bus_driver *drv = to_bus_driver(dev->driver);
> > > >     struct bus_device *dev = to_bus_device(_dev);
> > > >
> > > >     if (drv->remove)
> > > >         drv->remove(dev);
> > > >     dev_pm_domain_detach(_dev);
> > > > }
> > > >
> > > > When the driver's probe function uses devres-managed resources that depend
> > > > on the power domain state, those resources are released later during
> > > > device_unbind_cleanup().
> > > >
> > > > Releasing devres-managed resources that depend on the power domain state
> > > > after detaching the device from its PM domain can cause failures.
> > > >
> > > > For example, if the driver uses devm_pm_runtime_enable() in its probe
> > > > function, and the device's clocks are managed by the PM domain, then
> > > > during removal the runtime PM is disabled in device_unbind_cleanup() after
> > > > the clocks have been removed from the PM domain. It may happen that the
> > > > devm_pm_runtime_enable() action causes the device to be runtime-resumed.
> > >
> > > Don't use devm_pm_runtime_enable() then.
> >
> > What about other devm_ APIs? Are you suggesting that platform drivers
> > should not be using devm_clk*(), devm_regulator_*(),
> > devm_request_*_irq() and devm_add_action_or_reset()? Because again,
> > dev_pm_domain_detach() that is called by platform bus_remove() may shut
> > off the device too early, before cleanup code has a chance to execute
> > proper cleanup.
> >
> > The issue is not limited to runtime PM.
> >
> > >
> > > > If the driver specific runtime PM APIs access registers directly, this
> > > > will lead to accessing device registers without clocks being enabled.
> > > > Similar issues may occur with other devres actions that access device
> > > > registers.
> > > >
> > > > Add devm_pm_domain_attach(). When replacing the dev_pm_domain_attach() and
> > > > dev_pm_domain_detach() in bus probe and bus remove, it ensures that the
> > > > device is detached from its PM domain in device_unbind_cleanup(), only
> > > > after all driver's devres-managed resources have been release.
> > > >
> > > > For flexibility, the implemented devm_pm_domain_attach() has 2 state
> > > > arguments, one for the domain state on attach, one for the domain state on
> > > > detach.
> > >
> > > dev_pm_domain_attach() is not part driver API and I'm not convinced at
> >
> > Is the concern that devm_pm_domain_attach() will be [ab]used by drivers?
>
> Yes, among other things.

This would be much less objectionable to me if it were not devm_, but
also the current expectation is that the PM domain will be gone after
device_remove() has returned.