linux-kernel - Re: [PATCH v5 1/3] cpuidle: psci: Call cpu_cluster_pm

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Message-ID: <20220217022851.GB31965@dragon>
Date:   Thu, 17 Feb 2022 10:28:53 +0800
From:   Shawn Guo <shawn.guo@...aro.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Maulik Shah <quic_mkshah@...cinc.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/3] cpuidle: psci: Call cpu_cluster_pm_enter() on the
 last CPU

On Wed, Feb 16, 2022 at 02:39:26PM +0000, Marc Zyngier wrote:
> On 2022-02-16 13:28, Shawn Guo wrote:
> > Make a call to cpu_cluster_pm_enter() on the last CPU going to low power
> > state (and cpu_cluster_pm_exit() on the firt CPU coming back), so that
> > platforms can be notified to set up hardware for getting into the
> > cluster
> > low power state.
> > 
> > Signed-off-by: Shawn Guo <shawn.guo@...aro.org>
> > ---
> >  drivers/cpuidle/cpuidle-psci.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/drivers/cpuidle/cpuidle-psci.c
> > b/drivers/cpuidle/cpuidle-psci.c
> > index b51b5df08450..c748c1a7d7b1 100644
> > --- a/drivers/cpuidle/cpuidle-psci.c
> > +++ b/drivers/cpuidle/cpuidle-psci.c
> > @@ -37,6 +37,7 @@ struct psci_cpuidle_data {
> >  static DEFINE_PER_CPU_READ_MOSTLY(struct psci_cpuidle_data,
> > psci_cpuidle_data);
> >  static DEFINE_PER_CPU(u32, domain_state);
> >  static bool psci_cpuidle_use_cpuhp;
> > +static atomic_t cpus_in_idle;
> > 
> >  void psci_set_domain_state(u32 state)
> >  {
> > @@ -67,6 +68,14 @@ static int __psci_enter_domain_idle_state(struct
> > cpuidle_device *dev,
> >  	if (ret)
> >  		return -1;
> > 
> > +	if (atomic_inc_return(&cpus_in_idle) == num_online_cpus()) {
> > +		ret = cpu_cluster_pm_enter();
> > +		if (ret) {
> > +			ret = -1;
> > +			goto dec_atomic;
> > +		}
> > +	}
> > +
> >  	/* Do runtime PM to manage a hierarchical CPU toplogy. */
> >  	rcu_irq_enter_irqson();
> >  	if (s2idle)
> > @@ -88,6 +97,10 @@ static int __psci_enter_domain_idle_state(struct
> > cpuidle_device *dev,
> >  		pm_runtime_get_sync(pd_dev);
> >  	rcu_irq_exit_irqson();
> > 
> > +	if (atomic_read(&cpus_in_idle) == num_online_cpus())
> > +		cpu_cluster_pm_exit();
> > +dec_atomic:
> > +	atomic_dec(&cpus_in_idle);
> >  	cpu_pm_exit();
> > 
> >  	/* Clear the domain state to start fresh when back from idle. */
> 
> Is it just me, or does anyone else find it a bit odd that a cpuidle driver
> calls back into the core cpuidle code to generate new events?

It's not uncommon that a platform driver calls some helper functions
provided by core.

> Also, why is this PSCI specific? I would assume that the core cpuidle code
> should be responsible for these transitions, not a random cpuidle driver.

The CPU PM helpers cpu_pm_enter() and cpu_cluster_pm_enter() are provided
by kernel/cpu_pm.c rather than cpuidle core.  This PSCI cpuidle driver
already uses cpu_pm_enter(), and my patch is making a call to
cpu_cluster_pm_enter().

Shawn