[PATCH] Input: applespi - turn the keyboard backlight off across suspend

[Michal Szpakowski <michi.szpakowski@gmail.com>]

The keyboard backlight of the SPI topcase stays lit through s2idle: the
driver's suspend handler only switches the caps-lock LED off, and the
backlight LED is registered without LED_CORE_SUSPENDRESUME, so the LED
core never gets to blank it. Under deep (S3) the rails go down anyway,
which is why it only shows on machines that default to s2idle.

Set the flag. The LED core then sets the brightness to 0 before the
device suspends and restores the previous level on resume; the LED is a
child of the SPI device, so the command goes out before applespi_suspend()
drains its writes and disables the GPE.

Tested on a MacBookPro13,1 (2016): 30 s of s2idle with the backlight at
200/255 leaves it lit on the stock kernel; with the flag it goes dark at
suspend and is back at 200 on wake.

Fixes: 038b1a05eae6 ("Input: add Apple SPI keyboard and trackpad driver")
Cc: stable@vger.kernel.org
Signed-off-by: Michal Szpakowski <michi.szpakowski@gmail.com>
---
 drivers/input/keyboard/applespi.c | 1 +
 1 file changed, 1 insertion(+)

--- a/drivers/input/keyboard/applespi.c
+++ b/drivers/input/keyboard/applespi.c
@@ -1772,6 +1772,7 @@
 	applespi->backlight_info.name            = "spi::kbd_backlight";
 	applespi->backlight_info.default_trigger = "kbd-backlight";
 	applespi->backlight_info.brightness_set  = applespi_set_bl_level;
+	applespi->backlight_info.flags           = LED_CORE_SUSPENDRESUME;
 
 	sts = devm_led_classdev_register(&spi->dev, &applespi->backlight_info);
 	if (sts)