[PATCH v3 7/7] platform/x86: thinkpad_acpi: Reconcile EC level on resume

[Qiling Zhu <kmatzkaczor244@gmail.com>]

The firmware does not always restore the keyboard backlight level across
sleep: after hibernation from auto mode the EC comes back with the
backlight off, without emitting a notification.  The cached level and a
possibly still-active auto trigger then desynchronize from the hardware
until the next user action.

Check the EC level on resume on auto-mode machines and route it through
the regular notification path, which also deactivates the auto trigger
if the firmware left auto mode.

Signed-off-by: Qiling Zhu <kmatzkaczor244@gmail.com>
---
 drivers/platform/x86/lenovo/thinkpad_acpi.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/x86/lenovo/thinkpad_acpi.c b/drivers/platform/x86/lenovo/thinkpad_acpi.c
index f11e61417..802e0d53b 100644
--- a/drivers/platform/x86/lenovo/thinkpad_acpi.c
+++ b/drivers/platform/x86/lenovo/thinkpad_acpi.c
@@ -5395,13 +5395,22 @@ static void kbdlight_suspend(void)
 	led_classdev_suspend(led_cdev);
 }
 
+static void kbdlight_notify_change(void);
+
 static void kbdlight_resume(void)
 {
 	if (!tp_features.kbdlight)
 		return;
 
-	if (tp_features.kbdlight_auto)
+	if (tp_features.kbdlight_auto) {
+		/*
+		 * The firmware may not restore auto mode: after hibernation
+		 * from level 3 it comes back with the backlight off.  Check
+		 * the EC level and reconcile.
+		 */
+		kbdlight_notify_change();
 		return;
+	}
 
 	led_classdev_resume(&tpacpi_led_kbdlight.led_classdev);
 }
-- 
2.56.1