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

[Maulik Shah]

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
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.

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 <maulik.shah at oss.qualcomm.com>
---
 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