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 <[email protected]>
Reviewed-by: Ulf Hansson <[email protected]>
Tested-by: Adrien Thierry <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>

diff --git a/drivers/cpuidle/Kconfig.arm b/drivers/cpuidle/Kconfig.arm
index f0714a32921e6889387a0b9b0471a0cc45bb9209..a1ee475d180dacab245510674514811aec337ad3 100644 (file)
--- a/drivers/cpuidle/Kconfig.arm
+++ b/drivers/cpuidle/Kconfig.arm
@@ -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

diff --git a/drivers/cpuidle/cpuidle-psci-domain.c b/drivers/cpuidle/cpuidle-psci-domain.c
index c80cf9ddabd8a19a42436892a9caeb288a4188e3..6ad2954948a5abb2f9612d4e52832d73ef25020d 100644 (file)
--- a/drivers/cpuidle/cpuidle-psci-domain.c
+++ b/drivers/cpuidle/cpuidle-psci-domain.c
@@ -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;

diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index 57bc3e3ae3912a3af075446ec5e8f94484588a91..68467a325dcb1810616fa787a43c0eb6a2980e3c 100644 (file)
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c
@@ -231,6 +231,9 @@ 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);