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 runtime PM calls from cpuidle-psci, which effectively stops suspending the cpuidle PSCI domain. This is a trade-off between making PREEMPT_RT working and still having a proper power domain hierarchy in the system. Cc: Adrien Thierry <athierry@xxxxxxxxxx> Cc: Brian Masney <bmasney@xxxxxxxxxx> Cc: linux-rt-users@xxxxxxxxxxxxxxx Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> --- Changes since v1: 1. Re-work commit msg. 2. Add note to Kconfig. Several other patches were dropped, as this is the only one actually needed. It effectively stops PSCI cpuidle power domains from suspending thus solving all other issues I experienced. --- drivers/cpuidle/Kconfig.arm | 3 +++ drivers/cpuidle/cpuidle-psci.c | 4 ++-- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/cpuidle/Kconfig.arm b/drivers/cpuidle/Kconfig.arm index 747aa537389b..24429b5bfd1c 100644 --- a/drivers/cpuidle/Kconfig.arm +++ b/drivers/cpuidle/Kconfig.arm @@ -24,6 +24,9 @@ config ARM_PSCI_CPUIDLE It provides an idle driver that is capable of detecting and managing idle states through the PSCI firmware interface. + The driver is not yet compatible with PREEMPT_RT: no idle states will + be entered by CPUs on such kernel. + config ARM_PSCI_CPUIDLE_DOMAIN bool "PSCI CPU idle Domain" depends on ARM_PSCI_CPUIDLE diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c index 312a34ef28dc..c25592718984 100644 --- a/drivers/cpuidle/cpuidle-psci.c +++ b/drivers/cpuidle/cpuidle-psci.c @@ -66,7 +66,7 @@ static __cpuidle int __psci_enter_domain_idle_state(struct cpuidle_device *dev, /* Do runtime PM to manage a hierarchical CPU toplogy. */ if (s2idle) dev_pm_genpd_suspend(pd_dev); - else + else if (!IS_ENABLED(CONFIG_PREEMPT_RT)) pm_runtime_put_sync_suspend(pd_dev); state = psci_get_domain_state(); @@ -77,7 +77,7 @@ static __cpuidle int __psci_enter_domain_idle_state(struct cpuidle_device *dev, if (s2idle) dev_pm_genpd_resume(pd_dev); - else + else if (!IS_ENABLED(CONFIG_PREEMPT_RT)) pm_runtime_get_sync(pd_dev); cpu_pm_exit(); -- 2.34.1
