linux-kernel - [PATCH v1 4/5] ACPI: processor: Rescan "dead" SMT siblings during initialization

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Message-ID: <2005721.PYKUYFuaPT@rjwysocki.net>
Date: Thu, 05 Jun 2025 17:07:31 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: x86 Maintainers <x86@...nel.org>, Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
 "Gautham R. Shenoy" <gautham.shenoy@....com>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Linux ACPI <linux-acpi@...r.kernel.org>
Subject:
 [PATCH v1 4/5] ACPI: processor: Rescan "dead" SMT siblings during
 initialization

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Make acpi_processor_driver_init() call arch_cpu_rescan_dead_smt_siblings(),
via a new wrapper function called acpi_idle_rescan_dead_smt_siblings(),
after successfully initializing the driver, to allow the "dead" SMT
siblings to go into deep idle states, which is necessary for the
processor to be able to reach deep package C-states (like PC10) going
forward, so that power can be reduced sufficiently in suspend-to-idle,
among other things.

However, do it only if the ACPI idle driver is the current cpuidle
driver (otherwise it is assumed that another cpuidle driver will take
care of this) and avoid doing it on architectures other than x86.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/acpi/internal.h         |    6 ++++++
 drivers/acpi/processor_driver.c |    3 +++
 drivers/acpi/processor_idle.c   |    8 ++++++++
 3 files changed, 17 insertions(+)

--- a/drivers/acpi/internal.h
+++ b/drivers/acpi/internal.h
@@ -175,6 +175,12 @@
 static inline void acpi_early_processor_control_setup(void) {}
 #endif

+#ifdef CONFIG_ACPI_PROCESSOR_CSTATE
+void acpi_idle_rescan_dead_smt_siblings(void);
+#else
+static inline void acpi_idle_rescan_dead_smt_siblings(void) {}
+#endif
+
 /* --------------------------------------------------------------------------
                                   Embedded Controller
    -------------------------------------------------------------------------- */
--- a/drivers/acpi/processor_driver.c
+++ b/drivers/acpi/processor_driver.c
@@ -279,6 +279,9 @@
 	 * after acpi_cppc_processor_probe() has been called for all online CPUs
 	 */
 	acpi_processor_init_invariance_cppc();
+
+	acpi_idle_rescan_dead_smt_siblings();
+
 	return 0;
 err:
 	driver_unregister(&acpi_processor_driver);
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -24,6 +24,8 @@
 #include <acpi/processor.h>
 #include <linux/context_tracking.h>

+#include "internal.h"
+
 /*
  * Include the apic definitions for x86 to have the APIC timer related defines
  * available also for UP (on SMP it gets magically included via linux/smp.h).
@@ -55,6 +57,12 @@
 };

 #ifdef CONFIG_ACPI_PROCESSOR_CSTATE
+void acpi_idle_rescan_dead_smt_siblings(void)
+{
+	if (cpuidle_get_driver() == &acpi_idle_driver)
+		arch_cpu_rescan_dead_smt_siblings();
+}
+
 static
 DEFINE_PER_CPU(struct acpi_processor_cx * [CPUIDLE_STATE_MAX], acpi_cstate);