[PATCH v3] 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 both ON and OFF token should be present to support keyboard
backlight.

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>
---

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