armbian-build/patch/kernel/archive/uefi-x86-7.2/9001-ACPI-x86-Apple-T2-systems-need-early-CPU-offlining.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Andre Eikmeyer <dev@deq.rocks>
Date: Fri, 24 Jul 2026 17:37:27 +0200
Subject: ACPI: x86: Apple T2 systems need early CPU offlining

Linux reports _OSI("Darwin") on x86 Apple systems. On T2 Macs, the
selected firmware suspend path makes secondary CPU startup during early
resume take several seconds per CPU. The same CPUs can be brought online
normally after platform resume.

We therefore move secondary CPU hotplug outside the generic CPU PM
notifier window on systems exposing the Apple T2 PCI bridge. A prepare
notifier runs before the CPU core blocks hotplug, while a post notifier
restores only the CPUs it removed after the core enables hotplug again.

This reduces CPU bring-up during resume from several seconds per CPU to a
fraction of a second. The change was tested on MacBookPro15,1,
MacBookPro16,2, MacBookAir9,1 and a 27-inch T2 iMac.

Signed-off-by: Andre Eikmeyer <dev@deq.rocks>
---
 drivers/acpi/x86/apple.c | 131 ++++++++++
 1 file changed, 131 insertions(+)

diff --git a/drivers/acpi/x86/apple.c b/drivers/acpi/x86/apple.c
index 111111111111..222222222222 100644
--- a/drivers/acpi/x86/apple.c
+++ b/drivers/acpi/x86/apple.c
@@ -6,7 +6,13 @@
 
 #include <linux/acpi.h>
 #include <linux/bitmap.h>
+#include <linux/cpu.h>
+#include <linux/cpuhplock.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+#include <linux/pci.h>
 #include <linux/platform_data/x86/apple.h>
+#include <linux/suspend.h>
 #include <linux/uuid.h>
 #include "../internal.h"
 
@@ -146,3 +152,128 @@ void acpi_extract_apple_properties(struct acpi_device *adev)
 	ACPI_FREE(props);
 	bitmap_free(valid);
 }
+
+#ifdef CONFIG_PM_SLEEP_SMP
+#define PCI_DEVICE_ID_APPLE_T2_BRIDGE 0x1801
+
+/*
+ * The ACPI path selected by _OSI("Darwin") leaves Apple T2 systems in a
+ * state where bringing secondary CPUs online during early resume may take
+ * several seconds per CPU. Normal CPU hotplug after platform resume is not
+ * affected, so move it outside the generic suspend CPU hotplug window.
+ */
+static cpumask_var_t apple_t2_offlined_cpus;
+
+static void apple_t2_restore_cpus(void)
+{
+	unsigned int cpu;
+	int ret;
+
+	for_each_cpu(cpu, apple_t2_offlined_cpus) {
+		ret = add_cpu(cpu);
+		if (ret) {
+			pr_err("ACPI: Apple T2 failed to restore CPU%u: %d\n",
+			       cpu, ret);
+			continue;
+		}
+
+		cpumask_clear_cpu(cpu, apple_t2_offlined_cpus);
+	}
+}
+
+static void apple_t2_offline_cpus(void)
+{
+	unsigned int cpu;
+	int ret;
+
+	if (!cpumask_empty(apple_t2_offlined_cpus)) {
+		pr_err("ACPI: Apple T2 CPUs from the previous suspend remain offline\n");
+		apple_t2_restore_cpus();
+		if (!cpumask_empty(apple_t2_offlined_cpus)) {
+			pr_err("ACPI: Apple T2 early CPU offlining skipped\n");
+			return;
+		}
+	}
+
+	for_each_online_cpu(cpu) {
+		if (cpu == 0)
+			continue;
+
+		ret = remove_cpu(cpu);
+		if (ret) {
+			pr_err("ACPI: Apple T2 failed to offline CPU%u: %d\n",
+			       cpu, ret);
+			continue;
+		}
+
+		cpumask_set_cpu(cpu, apple_t2_offlined_cpus);
+	}
+}
+
+static int apple_t2_cpu_prepare(struct notifier_block *nb,
+				unsigned long action, void *unused)
+{
+	if (action == PM_SUSPEND_PREPARE)
+		apple_t2_offline_cpus();
+
+	return NOTIFY_OK;
+}
+
+static int apple_t2_cpu_restore(struct notifier_block *nb,
+				unsigned long action, void *unused)
+{
+	if (action == PM_POST_SUSPEND)
+		apple_t2_restore_cpus();
+
+	return NOTIFY_OK;
+}
+
+/*
+ * The CPU core PM notifier runs at priority 0. Offline CPUs before it blocks
+ * hotplug, then restore them after it enables hotplug again.
+ */
+static struct notifier_block apple_t2_cpu_prepare_nb = {
+	.notifier_call = apple_t2_cpu_prepare,
+	.priority = 1,
+};
+
+static struct notifier_block apple_t2_cpu_restore_nb = {
+	.notifier_call = apple_t2_cpu_restore,
+	.priority = -1,
+};
+
+static int __init apple_t2_cpu_pm_init(void)
+{
+	struct pci_dev *t2;
+	int ret;
+
+	if (!x86_apple_machine)
+		return 0;
+
+	t2 = pci_get_device(PCI_VENDOR_ID_APPLE,
+			    PCI_DEVICE_ID_APPLE_T2_BRIDGE, NULL);
+	if (!t2)
+		return 0;
+	pci_dev_put(t2);
+
+	if (!alloc_cpumask_var(&apple_t2_offlined_cpus, GFP_KERNEL))
+		return -ENOMEM;
+
+	ret = register_pm_notifier(&apple_t2_cpu_prepare_nb);
+	if (ret)
+		goto free_mask;
+
+	ret = register_pm_notifier(&apple_t2_cpu_restore_nb);
+	if (ret)
+		goto unregister_prepare;
+
+	return 0;
+
+unregister_prepare:
+	unregister_pm_notifier(&apple_t2_cpu_prepare_nb);
+free_mask:
+	free_cpumask_var(apple_t2_offlined_cpus);
+	return ret;
+}
+late_initcall(apple_t2_cpu_pm_init);
+#endif
-- 
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