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

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Message-ID: <b690d382d989bd99eaf870e79f63cfb9@kernel.org>
Date:   Wed, 16 Feb 2022 14:39:26 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Shawn Guo <shawn.guo@...aro.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 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?

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.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...