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

From: Kai-Heng Feng
Date: Mon Jun 19 2017 - 23:05:42 EST

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

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

Change commit log - not all models have ON token.

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

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();

- 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;