[PATCH v4] platform/x86: dell-laptop: Fix bogus keyboard backlight sysfs interface

[Kai-Heng Feng]

Dell Latitude 3160 does not have keyboard backlight, but there is a
sysfs interface for it, which does nothing at all.

KBD_LED_ON_TOKEN is the only token can be found. Since it doesn't have
KBD_LED_OFF_TOKEN or KBD_LED_AUTO_*_TOKEN, it should be safe to assume
at least two tokens should be present to support keyboard backlight.
Not all models have ON token - they may have multiple AUTO tokens instead.

Models which do not use SMBIOS token to control keyboard backlight, also
have this issue. Brightness level is 0 on these models. Verified on Dell
Inspiron 3565.

Reports keyboard backlight is supported only when at least two modes are
present.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
---

v4:
Change commit log - not all models have ON token.

v3:
Change the logic, there should be at least two modes present to claim it
supports backlight. Suggested by Pali RohÃr.

v2:
The only token can be found is actually KBD_LED_ON_TOKEN, which is BIT(5),
instead of KBD_LED_OFF_TOKEN. Change commit log accordingly.

Use token bit to make the intention more clear.
Also consider kbd_mode_levels_count and kbd_info.levels, suggested by
Pali RohÃr.

Use XOR to simplify the bitmask comparison, suggested by
Andy Shevchenko.

 drivers/platform/x86/dell-laptop.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/x86/dell-laptop.c b/drivers/platform/x86/dell-laptop.c
index ec202094bd50..f42159fd2031 100644
--- a/drivers/platform/x86/dell-laptop.c
+++ b/drivers/platform/x86/dell-laptop.c
@@ -1510,7 +1510,11 @@ static void kbd_init(void)
 	ret = kbd_init_info();
 	kbd_init_tokens();
 
-	if (kbd_token_bits != 0 || ret == 0)
+	/*
+	 * Only supports keyboard backlight when it has at least two modes.
+	 */
+	if ((ret == 0 && (kbd_info.levels != 0 || kbd_mode_levels_count >= 2))
+	    || kbd_get_valid_token_counts() >= 2)
 		kbd_led_present = true;
 }
 
-- 
2.13.1