[PATCH] ACPI: x86: Apple T2 systems need early CPU offlining

[PATCH] ACPI: x86: Apple T2 systems need early CPU offlining

[Andre Eikmeyer]

Hello everyone,

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 T2 systems. 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 | 140 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 140 insertions(+)

diff --git a/drivers/acpi/x86/apple.c b/drivers/acpi/x86/apple.c
index 45d0f16..5595a6a 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 +152,137 @@ out_free:
 	ACPI_FREE(props);
 	bitmap_free(valid);
 }
+
+#ifdef CONFIG_PM_SLEEP_SMP
+/*
+ * 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 we move it outside the generic suspend CPU hotplug window.
+ */
+static cpumask_var_t apple_t2_offlined_cpus;
+
+#define PCI_DEVICE_ID_APPLE_T2_BRIDGE 0x1801
+
+static bool __init apple_t2_present(void)
+{
+	struct pci_dev *pdev;
+
+	if (!x86_apple_machine)
+		return false;
+
+	pdev = pci_get_device(PCI_VENDOR_ID_APPLE,
+			      PCI_DEVICE_ID_APPLE_T2_BRIDGE, NULL);
+	if (!pdev)
+		return false;
+
+	pci_dev_put(pdev);
+	return true;
+}
+
+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. We offline CPUs before
+ * hotplug is blocked, 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)
+{
+	int ret;
+
+	if (!apple_t2_present())
+		return 0;
+
+	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
-- 
2.55.0

Re: [PATCH] ACPI: x86: Apple T2 systems need early CPU offlining

[Lukas Wunner]

[cc += Chen Yu, start of thread is here:
https://lore.kernel.org/all/20260812120326.155226-1-dev@deq.rocks/
]

On Wed, Aug 12, 2026 at 02:03:26PM +0200, Andre Eikmeyer wrote:
> 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.

That's not a T2-specific issue.  It occurs on older Intel Macs as well.

Back in 2018, Chen Yu root-caused it to an invalid MTRR upon resume
from system sleep:

https://lore.kernel.org/all/20180319041843.28218-1-yu.c.chen@intel.com/

I've been using his patch for 8 years to reduce resume time on my
MacBookPro9,1.  Unfortunately it was never applied upstream for
reasons unknown.  It probably just slipped through the cracks.

You may want to test if his patch helps on T2 models as well.
I think it's a more generic solution to the problem than the one
you're proposing.

Thanks,

Lukas