Re: [PATCH 1/2] cpuidle: psci: Start CPU-cluster pmdomain OFF when OSI is used

On Tue, Aug 11, 2026 at 7:50 AM Maulik Shah
<[email protected]> wrote:
>
> psci_pd_init() always calls pm_genpd_init() with is_off=false, so a
> CPU-cluster pmdomain is marked ON at creation regardless of whether any
> CPU has actually powered it on yet. The pmdomain's own status tracking
> (and the power-on notifier chain fired from _genpd_power_on()) is
> therefore wrong from the outset for OSI mode.
>
> A concrete example: hamoa has 3 CPU clusters, each with 4 CPUs, under a
> single parent system-level pmdomain. Passing "maxcpus=4" on the kernel
> command line limits boot to the first 4 CPUs, so only cluster0 is ever
> actually powered on. Without this fix, cluster1 and cluster2 are still
> marked ON at creation regardless, since is_off is always false. Because
> none of their CPUs ever come online, neither dt_idle_attach_cpu() nor
> psci_idle_cpuhp_up() ever fires for them, so nothing subsequently

Why isn't dt_idle_attach_cpu() called for them?

If we pass "maxcpus=4" on the kernel command line, the
cpu_present_mask should still contain all CPUs which cpuidle-psci uses
when attaching CPU devices to their respective CPU PM domain. Or maybe
I am wrong here?

> drives those two domains to OFF - they stay marked ON for as long as
> the system runs. When cluster0's CPUs go idle and its pmdomain is
> powered off, the parent system-level pmdomain still sees cluster1 and
> cluster2 as ON and therefore never selects a system-level idle state,
> even though no CPU in those two clusters ever executed.

Doesn't genpd_provider_sync_state() get called for these domains,
allowing them to be turned off?

>
> Starting the domain OFF is safe under OSI:
>
>  - For CPUs already online by the time this driver probes,
>    dt_idle_attach_cpu() explicitly checks cpu_online() and calls
>    pm_runtime_get_sync() on the CPU's attach device, which resolves to
>    this same pmdomain and drives a real power-on immediately. This runs
>    from psci_cpuidle_probe(), a device_initcall, strictly after
>    psci_idle_init_domains()'s core_initcall has already created and
>    marked off every pmdomain, so there is no window where an online
>    CPU's domain is left off with nothing left to turn it on.
>
>  - For CPUs that come online later, psci_idle_cpuhp_up() (registered
>    via cpuhp_setup_state_nocalls(), which never invokes the callback
>    for already-online CPUs at registration time) powers the domain on
>    through the normal cpuhp AP_ONLINE path.
>
> Gate this on use_osi rather than applying it unconditionally: in
> non-OSI mode psci_pd_init() sets GENPD_FLAG_ALWAYS_ON, which
> independently blocks genpd_power_off() regardless of is_off, so the
> domain can never really be off there and marking it is_off=true would
> be misleading noise with no effect.
>
> Fixes: a65a397f2451 ("cpuidle: psci: Add support for PM domains by using genpd")
> Assisted-by: Claude:claude-sonnet-5
> Signed-off-by: Maulik Shah <[email protected]>

Kind regards
Uffe

> ---
>  drivers/cpuidle/cpuidle-psci-domain.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
> index b9e4ad7d43a3..fab9de648b17 100644
> --- a/drivers/cpuidle/cpuidle-psci-domain.c
> +++ b/drivers/cpuidle/cpuidle-psci-domain.c
> @@ -78,7 +78,19 @@ static int psci_pd_init(struct device_node *np, bool use_osi)
>         /* Use governor for CPU PM domains if it has some states to manage. */
>         pd_gov = pd->states ? &pm_domain_cpu_gov : NULL;
>
> -       ret = pm_genpd_init(pd, pd_gov, false);
> +       /*
> +        * Start the domain in the OFF state when OSI is in use, so that
> +        * genpd's own status tracking (and its power-on notifier chain)
> +        * reflects reality from the outset instead of reporting ON before
> +        * any CPU in the domain has actually requested it. This is safe:
> +        * dt_idle_attach_cpu() runtime-resumes the domain for every CPU
> +        * that is already online by the time this driver probes, and the
> +        * PSCI cpuidle cpuhp callbacks power it on/off for CPUs that come
> +        * online/offline afterwards. When OSI isn't in use, GENPD_FLAG_ALWAYS_ON
> +        * above keeps the domain powered regardless of is_off, so this has
> +        * no effect there.
> +        */
> +       ret = pm_genpd_init(pd, pd_gov, use_osi);
>         if (ret)
>                 goto free_pd_prov;
>
>
> --
> 2.43.0
>