[PATCH 4/5] s390/idle: Introduce cpuidle for s390
From: Mete Durlu
Date: Tue Jun 09 2026 - 03:53:17 EST
Introduce generic cpuidle driver on s390. Use a two stage approach to
handle idle scenarios and use TEO governor for idle stage selection.
Two stages are, from shallow to deep, idle polling and enabled wait.
Suggested-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
Suggested-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Signed-off-by: Mete Durlu <meted@xxxxxxxxxxxxx>
---
arch/s390/Kconfig | 5 ++
drivers/cpuidle/Kconfig | 5 ++
drivers/cpuidle/Kconfig.s390 | 12 ++++
drivers/cpuidle/Makefile | 4 ++
drivers/cpuidle/cpuidle-s390.c | 104 +++++++++++++++++++++++++++++++++
5 files changed, 130 insertions(+)
create mode 100644 drivers/cpuidle/Kconfig.s390
create mode 100644 drivers/cpuidle/cpuidle-s390.c
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index ecbcbb781e40..8548f5b6b247 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -20,6 +20,9 @@ config ARCH_HAS_ILOG2_U64
config ARCH_PROC_KCORE_TEXT
def_bool y
+config ARCH_HAS_CPU_RELAX
+ def_bool y
+
config GENERIC_HWEIGHT
def_bool !HAVE_MARCH_Z196_FEATURES
@@ -708,6 +711,8 @@ config KERNEL_IMAGE_BASE
endmenu
+source "drivers/cpuidle/Kconfig"
+
menu "Memory setup"
config ARCH_SPARSEMEM_ENABLE
diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index d6d8386d3f02..00e2562041fd 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig
@@ -71,6 +71,11 @@ depends on RISCV
source "drivers/cpuidle/Kconfig.riscv"
endmenu
+menu "S390 CPU Idle Drivers"
+depends on S390
+source "drivers/cpuidle/Kconfig.s390"
+endmenu
+
config HALTPOLL_CPUIDLE
tristate "Halt poll cpuidle driver"
depends on X86 && KVM_GUEST
diff --git a/drivers/cpuidle/Kconfig.s390 b/drivers/cpuidle/Kconfig.s390
new file mode 100644
index 000000000000..e51704a9304c
--- /dev/null
+++ b/drivers/cpuidle/Kconfig.s390
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# S390 CPU Idle drivers
+#
+
+config S390_CPUIDLE
+ bool "S390 CPU idle driver"
+ default y
+ help
+ Select this option to enable processor idle state management
+ through cpuidle subsystem.
+
diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
index 1de9e92c5b0f..88cbc2a7aea8 100644
--- a/drivers/cpuidle/Makefile
+++ b/drivers/cpuidle/Makefile
@@ -42,3 +42,7 @@ obj-$(CONFIG_POWERNV_CPUIDLE) += cpuidle-powernv.o
###############################################################################
# RISC-V drivers
obj-$(CONFIG_RISCV_SBI_CPUIDLE) += cpuidle-riscv-sbi.o
+
+###############################################################################
+# S390 drivers
+obj-$(CONFIG_S390_CPUIDLE) += cpuidle-s390.o
diff --git a/drivers/cpuidle/cpuidle-s390.c b/drivers/cpuidle/cpuidle-s390.c
new file mode 100644
index 000000000000..58b738ea0150
--- /dev/null
+++ b/drivers/cpuidle/cpuidle-s390.c
@@ -0,0 +1,104 @@
+// 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",
+ .governor = "teo",
+ .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;
+}
+
+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);
--
2.54.0