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cpuidle: psci: Do not suspend topology CPUs on PREEMPT_RT
The runtime Power Management of CPU topology is not compatible with PREEMPT_RT: 1. Core cpuidle path disables IRQs. 2. Core cpuidle calls cpuidle-psci. 3. cpuidle-psci in __psci_enter_domain_idle_state() calls pm_runtime_put_sync_suspend() and pm_runtime_get_sync() which use spinlocks (which are sleeping on PREEMPT_RT). Deep sleep modes are not a priority of Realtime kernels because the latencies might become unpredictable. On the other hand the PSCI CPU idle power domain is a parent of other devices and power domain controllers, thus it cannot be simply skipped (e.g. on Qualcomm SM8250). Disable the idle callbacks in cpuidle-psci and mark the domain as always on. This is a trade-off between making PREEMPT_RT working and still having a proper power domain hierarchy in the system. Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org> Tested-by: Adrien Thierry <athierry@redhat.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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@ -24,6 +24,14 @@ config ARM_PSCI_CPUIDLE
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It provides an idle driver that is capable of detecting and
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managing idle states through the PSCI firmware interface.
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The driver has limitations when used with PREEMPT_RT:
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- If the idle states are described with the non-hierarchical layout,
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all idle states are still available.
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- If the idle states are described with the hierarchical layout,
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only the idle states defined per CPU are available, but not the ones
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being shared among a group of CPUs (aka cluster idle states).
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config ARM_PSCI_CPUIDLE_DOMAIN
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bool "PSCI CPU idle Domain"
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depends on ARM_PSCI_CPUIDLE
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@ -64,8 +64,11 @@ static int psci_pd_init(struct device_node *np, bool use_osi)
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pd->flags |= GENPD_FLAG_IRQ_SAFE | GENPD_FLAG_CPU_DOMAIN;
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/* Allow power off when OSI has been successfully enabled. */
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if (use_osi)
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/*
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* Allow power off when OSI has been successfully enabled.
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* PREEMPT_RT is not yet ready to enter domain idle states.
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*/
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if (use_osi && !IS_ENABLED(CONFIG_PREEMPT_RT))
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pd->power_off = psci_pd_power_off;
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else
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pd->flags |= GENPD_FLAG_ALWAYS_ON;
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@ -231,6 +231,9 @@ static int psci_dt_cpu_init_topology(struct cpuidle_driver *drv,
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if (!psci_has_osi_support())
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return 0;
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if (IS_ENABLED(CONFIG_PREEMPT_RT))
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return 0;
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data->dev = psci_dt_attach_cpu(cpu);
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if (IS_ERR_OR_NULL(data->dev))
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return PTR_ERR_OR_ZERO(data->dev);
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