Re: [PATCH v3 4/5] cpuidle: psci: Initialize the PM domains in powered off state for OSI

[Dhruva G <goledhruva@gmail.com>]

On 07-09-2026 16:46, Ulf Hansson wrote:
> At the point when the PM domain and the topology are registered through the
> genpd subsystem, it's not really known whether corresponding CPUs are
> online and thus if the PM domain should be initialized as powered on or
> not. Instead this information becomes available when the CPU devices gets
> attached to their respective PM domain through dt_idle_attach_cpu().
> 
> This is a problem when using PSCI OS-initiated mode, as we may end up with
> a PM domain that has the genpd's status indicating it to be powered on,
> while it in fact may not be the case. In the less severe scenario, this
> leads to selecting a shallower domain idle state for the PM domain than
> necessary. A more critical problem is when a non-CPU device shares the PM
> domain, leading to their corresponding drivers not being able to trust the
> status of it.
> 
> Let's fix these problems by initializing the state for the genpd's to be
> powered off and in the deepest possible domain idle state, when using
> OS-initiated mode. The support for ->sync_state() is maintained by setting
> the GENPD_FLAG_POWER_UNKNOWN for the genpds in question.
> 
> Reported-by: Maulik Shah <maulik.shah@oss.qualcomm.com>
> Link: https://lore.kernel.org/all/20260811-domain_off_ss3-v1-0-6a0a0fc023f5@oss.qualcomm.com/
> Reviewed-by: Abel Vesa <abel.vesa@oss.qualcomm.com>
> Tested-by: Yuanfang Zhang <yuanfang.zhang@oss.qualcomm.com>
> Signed-off-by: Ulf Hansson <ulf.hansson@oss.qualcomm.com>
> ---
> 
> Changes in v3:
> 	- None.
> Changes in v2:
> 	- Fix a bug in the call to pm_genpd_init().
> 
> ---
>  drivers/cpuidle/cpuidle-psci-domain.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
> index b9e4ad7d43a3..4d8c63d329c2 100644
> --- a/drivers/cpuidle/cpuidle-psci-domain.c
> +++ b/drivers/cpuidle/cpuidle-psci-domain.c
> @@ -68,7 +68,8 @@ static int psci_pd_init(struct device_node *np, bool use_osi)
>  	 */
>  	if (use_osi) {
>  		pd->power_off = psci_pd_power_off;
> -		pd->flags |= GENPD_FLAG_ACTIVE_WAKEUP;
> +		pd->flags |= GENPD_FLAG_ACTIVE_WAKEUP | GENPD_FLAG_POWER_UNKNOWN;
> +		pd->state_idx = pd->state_count ? pd->state_count - 1 : 0;
>  		if (IS_ENABLED(CONFIG_PREEMPT_RT))
>  			pd->flags |= GENPD_FLAG_RPM_ALWAYS_ON;
>  	} else {
> @@ -78,7 +79,7 @@ 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);
> +	ret = pm_genpd_init(pd, pd_gov, use_osi);

If CONFIG_PREEMPT_RT=y,

psci_pd_init(use_osi=true)
  -> sets GENPD_FLAG_POWER_UNKNOWN
  -> sets GENPD_FLAG_RPM_ALWAYS_ON
  -> pm_genpd_init(..., is_off=true)
  -> genpd->status = GENPD_STATE_OFF
  -> RPM_ALWAYS_ON + OFF is rejected (pmdomain/core.c: pm_genpd_init() 
				      rejects an RPM_ALWAYS_ON domain whose initial state is OFF)
  -> return -EINVAL

Therefore, on a PREEMPT_RT platform using OSI and hierarchical PSCI domains, psci_cpuidle_domain_probe()
should fail while initializing the first domain. The genpd providers are then unavailable, so 
dt_idle_attach_cpu() fails during PSCI cpuidle initialization and the driver rolls back its CPU
registrations.

I don't have a device on me to test this path, perhaps one of the QC devices + RT config
can reproduce this?

Should PREEMPT_RT case instead initialize these domains as ON?

This might be safer here atleast:

ret = pm_genpd_init(pd, pd_gov,
		    use_osi && !IS_ENABLED(CONFIG_PREEMPT_RT));

Regards,
Dhruva