[RESEND PATCH v4 2/2] PM: ACPI: reboot: Reinstate S5 for reboot

[Kai-Heng Feng <kai.heng.feng@canonical.com>]

Commit d60cd06331a3 ("PM: ACPI: reboot: Use S5 for reboot") caused Dell
PowerEdge r440 hangs at reboot.

The issue is fixed by commit 2ca1c94ce0b6 ("tg3: Disable tg3 device on
system reboot to avoid triggering AER"), so use the new sysoff API to
reinstate S5 for reboot on ACPI-based systems.

Using S5 for reboot is default behavior under Windows, "A full shutdown
(S5) occurs when a system restart is requested" [1].

[1] https://docs.microsoft.com/en-us/windows/win32/power/system-power-state

Cc: Josef Bacik <josef@toxicpanda.com>
Suggested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
---
v4:
 - Add comment and add more info to commit message.
v3:
 - Use new API to invoke ACPI S5.
v2:
 - Use do_kernel_power_off_prepare() instead.

 drivers/acpi/sleep.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
index ad4b2987b3d6e..0b557c0d405ef 100644
--- a/drivers/acpi/sleep.c
+++ b/drivers/acpi/sleep.c
@@ -1088,6 +1088,14 @@ int __init acpi_sleep_init(void)
 		register_sys_off_handler(SYS_OFF_MODE_POWER_OFF,
 					 SYS_OFF_PRIO_FIRMWARE,
 					 acpi_power_off, NULL);
+
+		/*
+		 * Windows uses S5 for reboot, so some BIOSes depend on it to
+		 * perform proper reboot.
+		 */
+		register_sys_off_handler(SYS_OFF_MODE_RESTART_PREPARE,
+					 SYS_OFF_PRIO_FIRMWARE,
+					 acpi_power_off_prepare, NULL);
 	} else {
 		acpi_no_s5 = true;
 	}
-- 
2.37.2