[PATCH 4/4] ACPI: battery: Wake system on AC plug or unplug in over s2idle

[Mario Limonciello <superm1@kernel.org>]

From: Mario Limonciello <mario.limonciello@amd.com>

On Windows the OS will wake up when plugged or unplugged from AC adapter.
Depending upon whether the system was plugged in or unplugged will
determine whether the "display turns on".  If there is no user activity
for some time then it goes back to sleep.

In Linux plugging or unplugging an adapter will wake the SoC from HW
sleep but then the Linux kernel puts it right back into HW sleep
immediately unless there is another interrupt active (such as a PME or
GPIO).

To get closer to the Windows behavior, record the state of the battery
when going into suspend and compare it when updating battery status
during the s2idle loop. If it's changed, wake the system.

This can be restored to previous behavior by disabling the ACPI battery
device `power/wakeup` sysfs file.

Link: https://learn.microsoft.com/en-us/windows-hardware/design/device-experiences/modern-standby-wake-sources#environmental-context-changes-1
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/acpi/battery.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
index 72c8a509695e6..91f79927cc720 100644
--- a/drivers/acpi/battery.c
+++ b/drivers/acpi/battery.c
@@ -125,6 +125,7 @@ struct acpi_battery {
 	int state;
 	int power_unit;
 	int capacity_suspend;
+	int suspend_state;
 	unsigned long flags;
 };
 
@@ -1012,6 +1013,12 @@ static inline bool acpi_battery_should_wake(struct acpi_battery *battery)
 		return true;
 	}
 
+	if (battery->state != battery->suspend_state) {
+		pm_pr_dbg("Waking due to battery state changed from 0x%x to 0x%x",
+			  battery->suspend_state, battery->state);
+		return true;
+	}
+
 	return false;
 }
 
@@ -1313,6 +1320,7 @@ static int acpi_battery_suspend(struct device *dev)
 		return -EINVAL;
 
 	battery->capacity_suspend = battery->capacity_now;
+	battery->suspend_state = battery->state;
 
 	return 0;
 }
-- 
2.43.0