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// SPDX-License-Identifier: GPL-2.0-only
/*
* s390 generic CPU idle driver.
*
* Copyright IBM Corp. 2026
*/
#define pr_fmt(fmt) "CPUidle s390: " fmt
#include <linux/init.h>
#include <linux/cpuidle.h>
#include <linux/cpu.h>
#include <linux/sched/clock.h>
static __cpuidle int s390_enter_idle(struct cpuidle_device *dev,
struct cpuidle_driver *drv,
int index)
{
arch_cpu_idle();
return index;
}
static struct cpuidle_driver s390_cpuidle_driver = {
.cpumask = (struct cpumask *)cpu_present_mask,
.name = "s390-idle",
.states = {
{ /* entry 0 is for polling */},
{
.enter = s390_enter_idle,
.name = "IDLE",
.desc = "ENABLED WAIT",
},
},
.safe_state_index = 0,
.state_count = 2,
};
static int s390_cpuidle_cpu_online(unsigned int cpu)
{
struct cpuidle_device *dev = &per_cpu(cpuidle_dev, cpu);
int rc;
if (dev->registered) {
cpuidle_pause_and_lock();
rc = cpuidle_enable_device(dev);
cpuidle_resume_and_unlock();
if (rc)
pr_err("Failed to enable cpuidle device on cpu %u\n", cpu);
} else {
dev->cpu = cpu;
rc = cpuidle_register_device(dev);
if (rc)
pr_err("Failed to register cpuidle driver on cpu %u\n", cpu);
}
return rc;
}
static int s390_cpuidle_cpu_dead(unsigned int cpu)
{
struct cpuidle_device *dev = &per_cpu(cpuidle_dev, cpu);
if (!dev->registered)
return 0;
cpuidle_pause_and_lock();
cpuidle_disable_device(dev);
cpuidle_resume_and_unlock();
return 0;
}
/*
* The target_residency and exit_latency values are benchmark-derived estimates
* that remain non-deterministic due to s390's virtualized architecture.
*
* Configuration strategy:
* - Poll idle state: Values derived from the next enabled idle state (EW)
* - Enabled Wait state: Values selected based on idle behavior and empirical
* measurement data
*
* Goal is to improve responsiveness for workloads with frequent sleep/wakeup
* cycles while minimizing any side effects.
*/
static void __init s390_cpuidle_ew_tune(void)
{
struct cpuidle_state *state = &s390_cpuidle_driver.states[1];
if (machine_is_lpar()) {
state->target_residency = 5;
state->exit_latency = 5;
} else {
state->target_residency = 1;
state->exit_latency = 1;
}
}
static int __init s390_cpuidle_init(void)
{
int rc;
s390_cpuidle_ew_tune();
cpuidle_poll_state_init(&s390_cpuidle_driver);
rc = cpuidle_register(&s390_cpuidle_driver, NULL);
if (rc)
return rc;
rc = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
"cpuidle/s390:online",
s390_cpuidle_cpu_online,
s390_cpuidle_cpu_dead);
if (rc < 0) {
cpuidle_unregister(&s390_cpuidle_driver);
pr_err("Failed to allocate hotplug state: cpuidle/s390:online\n");
return rc;
}
return 0;
}
device_initcall(s390_cpuidle_init);
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