platform/x86: ideapad-laptop: Fix FnLock not remembered among boots

On devices supported by ideapad-laptop, the HW/FW can remember the
FnLock state among boots. However, since the introduction of the FnLock
LED class device, it is turned off while shutting down, as a side effect
of the LED class device unregistering sequence.

Many users always turn on FnLock because they use function keys much
more frequently than multimedia keys. The behavior change is
inconvenient for them. Thus, set LED_RETAIN_AT_SHUTDOWN on the LED class
device so that the FnLock state gets remembered, which also aligns with
the behavior of manufacturer utilities on Windows.

Fixes: 07f48f6 ("platform/x86: ideapad-laptop: add FnLock LED class device")
Cc: [email protected]
Signed-off-by: Rong Zhang <[email protected]>
Reviewed-by: Hans de Goede <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Ilpo Järvinen <[email protected]>
Signed-off-by: Ilpo Järvinen <[email protected]>

Author: Rongronggg9

drivers/platform/x86/ideapad-laptop.c

@@ -1728,7 +1728,7 @@ static int ideapad_fn_lock_led_init(struct ideapad_private *priv)
 	priv->fn_lock.led.name                    = "platform::" LED_FUNCTION_FNLOCK;
 	priv->fn_lock.led.brightness_get          = ideapad_fn_lock_led_cdev_get;
 	priv->fn_lock.led.brightness_set_blocking = ideapad_fn_lock_led_cdev_set;
-	priv->fn_lock.led.flags                   = LED_BRIGHT_HW_CHANGED;
+	priv->fn_lock.led.flags                   = LED_BRIGHT_HW_CHANGED | LED_RETAIN_AT_SHUTDOWN;
 
 	err = led_classdev_register(&priv->platform_device->dev, &priv->fn_lock.led);
 	if (err)