[PATCH v3 1/7] platform/x86: thinkpad_acpi: Report auto keyboard backlight mode as off

[Qiling Zhu <kmatzkaczor244@gmail.com>]

The EC keyboard backlight level 3, which selects the auto mode, is
passed to the LED classdev verbatim by kbdlight_sysfs_get().  The LED
then reports a brightness of 3 with max_brightness 2, both through the
brightness sysfs attribute and through brightness_hw_changed
notifications.

This is not only cosmetic: UPower 1.91.x treats the out-of-range value as
invalid and stops watching brightness_hw_changed altogether, so the desktop
stops following the Fn+Space hotkey once auto mode has been entered.

The auto mode is not a brightness level.  Map it to 0, the value it is
reported as most of the time anyway, in line with what ideapad-laptop
already does for its auto mode.

Fixes: bb28f3d51ff5 ("thinkpad_acpi: Add support for keyboard backlight")
Reported-by: Andrea Rabbaglietti <rabbagliettiandrea@gmail.com>
Closes: https://lore.kernel.org/r/CAENjc+w0Rqy=kDSew7XtNJCSvyPiXPJ5faWdmCr5RGYFhpunCA@mail.gmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Qiling Zhu <kmatzkaczor244@gmail.com>
---
 drivers/platform/x86/lenovo/thinkpad_acpi.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/x86/lenovo/thinkpad_acpi.c b/drivers/platform/x86/lenovo/thinkpad_acpi.c
index 4f81855ad..2c3f8cf32 100644
--- a/drivers/platform/x86/lenovo/thinkpad_acpi.c
+++ b/drivers/platform/x86/lenovo/thinkpad_acpi.c
@@ -5102,6 +5102,9 @@ static struct ibm_struct video_driver_data = {
  * Keyboard backlight subdriver
  */
 
+/* EC level that selects the auto mode for the keyboard backlight */
+#define TPACPI_KBD_LIGHT_AUTO_LEVEL 3
+
 static enum led_brightness kbdlight_brightness;
 static DEFINE_MUTEX(kbdlight_mutex);
 
@@ -5191,7 +5194,8 @@ static enum led_brightness kbdlight_sysfs_get(struct led_classdev *led_cdev)
 	int level;
 
 	level = kbdlight_get_level();
-	if (level < 0)
+	/* Auto mode is not a brightness level; report it as off. */
+	if (level < 0 || level == TPACPI_KBD_LIGHT_AUTO_LEVEL)
 		return 0;
 
 	return level;
-- 
2.56.1