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cpuidle: psci: Do not suspend topology CPUs on PREEMPT_RT

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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>
This commit is contained in:
Krzysztof Kozlowski 2023-01-25 12:34:18 +01:00 committed by Rafael J. Wysocki
parent 41204a6076
commit f9901f6453
3 changed files with 16 additions and 2 deletions
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8
drivers/cpuidle/Kconfig.arm
View File

@ -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

7
drivers/cpuidle/cpuidle-psci-domain.c
View File

@ -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;

3
drivers/cpuidle/cpuidle-psci.c
View File

@ -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);