[PATCH v5 11/11] PM: Use hibernate flows for system power off

["Mario Limonciello (AMD)" <superm1@kernel.org>]

When the system is powered off the kernel will call device_shutdown()
which will issue callbacks into PCI core to wake up a device and call
it's shutdown() callback.  This will leave devices in ACPI D0 which can
cause some devices to misbehave with spurious wakeups and also leave some
devices on which will consume power needlessly.

The issue won't happen if the device is in D3 before system shutdown, so
putting device to low power state before shutdown solves the issue.

ACPI Spec 6.5, "7.4.2.5 System \_S4 State" says "Devices states are
compatible with the current Power Resource states. In other words, all
devices are in the D3 state when the system state is S4."

The following "7.4.2.6 System \_S5 State (Soft Off)" states "The S5
state is similar to the S4 state except that OSPM does not save any
context." so it's safe to assume devices should be at D3 for S5.

To accomplish this, use the PMSG_POWEROFF event to call all the device
hibernate callbacks when the kernel is compiled with hibernate support.
If compiled without hibernate support or hibernate fails fall back into
the previous shutdown flow.

Cc: AceLan Kao <acelan.kao@canonical.com>
Cc: Kai-Heng Feng <kaihengf@nvidia.com>
Cc: Mark Pearson <mpearson-lenovo@squebb.ca>
Cc: Merthan Karakaş <m3rthn.k@gmail.com>
Tested-by: Eric Naim <dnaim@cachyos.org>
Tested-by: Denis Benato <benato.denis96@gmail.com>
Link: https://lore.kernel.org/linux-pci/20231213182656.6165-1-mario.limonciello@amd.com/
Link: https://lore.kernel.org/linux-pci/20250506041934.1409302-1-superm1@kernel.org/
Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
---
v5:
 * split to multiple commits, re-order
v4:
 * https://lore.kernel.org/linux-pci/20250616175019.3471583-1-superm1@kernel.org/
v3:
 * Add new PMSG_POWEROFF and PM_EVENT_POWEROFF which alias to poweroff
   callbacks
 * Don't try to cleanup on dpm_suspend_start() or dpm_suspend_end() failures
   Jump right into normal shutdown flow instead.
 * https://lore.kernel.org/linux-pm/20250609024619.407257-1-superm1@kernel.org/T/#me6db0fb946e3d604a8f3d455128844ed802c82bb
---
 kernel/reboot.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index ec087827c85cd..c8835f8e5f271 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -13,6 +13,7 @@
 #include <linux/kexec.h>
 #include <linux/kmod.h>
 #include <linux/kmsg_dump.h>
+#include <linux/pm.h>
 #include <linux/reboot.h>
 #include <linux/suspend.h>
 #include <linux/syscalls.h>
@@ -305,6 +306,11 @@ static void kernel_shutdown_prepare(enum system_states state)
 		(state == SYSTEM_HALT) ? SYS_HALT : SYS_POWER_OFF, NULL);
 	system_state = state;
 	usermodehelper_disable();
+#ifdef CONFIG_HIBERNATE_CALLBACKS
+	if (!dpm_suspend_start(PMSG_POWEROFF) && !dpm_suspend_end(PMSG_POWEROFF))
+		return;
+	pr_emerg("Failed to power off devices, using shutdown instead.\n");
+#endif
 	device_shutdown();
 }
 /**
-- 
2.43.0