Commit f9901f64 authored by Krzysztof Kozlowski's avatar Krzysztof Kozlowski Committed by Rafael J. Wysocki
Browse files

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: default avatarKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
Tested-by: default avatarAdrien Thierry <athierry@redhat.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 41204a60

drivers/cpuidle/Kconfig.arm

+8 −0
Original line number Diff line number Diff line
@@ -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

drivers/cpuidle/cpuidle-psci-domain.c

+5 −2
Original line number Diff line number Diff line
@@ -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;

drivers/cpuidle/cpuidle-psci.c

+3 −0
Original line number Diff line number Diff line
@@ -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);