@@ -24,6 +24,14 @@ 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 has limitations when used with PREEMPT_RT:
+ - If the idle states are described with the non-hierarchical layout,
+ all idle states are still available.
+
+ - If the idle states are described with the hierarchical layout,
+ only the idle states defined per CPU are available, but not the ones
+ being shared among a group of CPUs (aka cluster idle states).
+
config ARM_PSCI_CPUIDLE_DOMAIN
bool "PSCI CPU idle Domain"
depends on ARM_PSCI_CPUIDLE
@@ -64,8 +64,11 @@ static int psci_pd_init(struct device_node *np, bool use_osi)
pd->flags |= GENPD_FLAG_IRQ_SAFE | GENPD_FLAG_CPU_DOMAIN;
- /* Allow power off when OSI has been successfully enabled. */
- if (use_osi)
+ /*
+ * Allow power off when OSI has been successfully enabled.
+ * PREEMPT_RT is not yet ready to enter domain idle states.
+ */
+ if (use_osi && !IS_ENABLED(CONFIG_PREEMPT_RT))
pd->power_off = psci_pd_power_off;
else
pd->flags |= GENPD_FLAG_ALWAYS_ON;
@@ -222,6 +222,9 @@ static int psci_dt_cpu_init_topology(struct cpuidle_driver *drv,
if (!psci_has_osi_support())
return 0;
+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
+ return 0;
+
data->dev = psci_dt_attach_cpu(cpu);
if (IS_ERR_OR_NULL(data->dev))
return PTR_ERR_OR_ZERO(data->dev);
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. Cc: Adrien Thierry <athierry@redhat.com> Cc: Brian Masney <bmasney@redhat.com> Cc: linux-rt-users@vger.kernel.org Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> --- Changes since v3: 1. Rework - disable idle states, mark as always on (Ulf). 2. Extend Kconfig warning (Ulf). 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 | 8 ++++++++ drivers/cpuidle/cpuidle-psci-domain.c | 7 +++++-- drivers/cpuidle/cpuidle-psci.c | 3 +++ 3 files changed, 16 insertions(+), 2 deletions(-)