platform/x86: lg-laptop: Fix keyboard backlight support on LG Gram 16T90SP

On the LG Gram 16T90SP, the ACPI firmware will only accept the values
0x80, 0xA2 and 0xA4 when setting the keyboard backlight. After a bit
of research using ACPI tables from older models it seems that bit 8
is supposed to be always written as 1.

Fix the keyboard backlight support on this model by always setting
bit 8 inside the argument passed to the WMAB ACPI control method.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20260708195553.7762-6-W_Armin@gmx.de
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

1 files changed, 36 insertions, 11 deletions

diff --git a/drivers/platform/x86/lg-laptop.c b/drivers/platform/x86/lg-laptop.c
index 164012c1c409..36ad1e269443 100644
--- a/drivers/platform/x86/lg-laptop.c
+++ b/drivers/platform/x86/lg-laptop.c
@@ -88,6 +88,18 @@ MODULE_PARM_DESC(fw_debug, "Enable printing of firmware debug messages");
 #define WMBB_USB_CHARGE 0x10B
 #define WMBB_BATT_LIMIT 0x10C
 
+#define KBD_LED_BRIGHTNESS_MASK GENMASK(4, 0)
+#define KBD_LED_BRIGHTNESS_OFF	0x0
+#define KBD_LED_BRIGHTNESS_HALF 0x2
+#define KBD_LED_BRIGHTNESS_FULL 0x4
+#define KBD_LED_MODE_MASK	GENMASK(6, 5)
+#define KBD_LED_MODE_OFF	0x0
+#define KBD_LED_MODE_ON		0x1
+#define KBD_LED_STATUS		BIT(7)
+#define KBD_LED_MAGIC_MASK	GENMASK(15, 8)
+/* Exact purpose is unknown, maybe some sort of brightness limit? */
+#define KBD_LED_MAGIC		0x05
+
 #define FAN_MODE_LOWER GENMASK(1, 0)
 #define FAN_MODE_UPPER GENMASK(5, 4)
 
@@ -603,15 +615,25 @@ static LED_DEVICE(tpad_led, 1, 0);
 static void kbd_backlight_set(struct led_classdev *cdev,
 			      enum led_brightness brightness)
 {
-	u32 val;
+	/* Must always be written */
+	u32 value = KBD_LED_STATUS;
+	u32 mode, bright;
+
+	if (brightness <= LED_OFF) {
+		mode = KBD_LED_MODE_OFF;
+		bright = KBD_LED_BRIGHTNESS_OFF;
+	} else {
+		mode = KBD_LED_MODE_ON;
+		if (brightness >= LED_FULL)
+			bright = KBD_LED_BRIGHTNESS_FULL;
+		else
+			bright = KBD_LED_BRIGHTNESS_HALF;
+	}
 
-	val = 0x22;
-	if (brightness <= LED_OFF)
-		val = 0;
-	if (brightness >= LED_FULL)
-		val = 0x24;
+	value |= FIELD_PREP(KBD_LED_BRIGHTNESS_MASK, bright);
+	value |= FIELD_PREP(KBD_LED_MODE_MASK, mode);
 
-	lg_wmab_set(cdev->dev->parent, WM_KEY_LIGHT, val);
+	lg_wmab_set(cdev->dev->parent, WM_KEY_LIGHT, value);
 }
 
 static enum led_brightness get_kbd_backlight_level(struct device *dev)
@@ -623,13 +645,16 @@ static enum led_brightness get_kbd_backlight_level(struct device *dev)
 	if (ret < 0)
 		return LED_OFF;
 
-	if ((value & 0xFF00) != 0x0500)
+	if (FIELD_GET(KBD_LED_MAGIC_MASK, value) != KBD_LED_MAGIC)
+		return LED_OFF;
+
+	if (FIELD_GET(KBD_LED_MODE_MASK, value) == KBD_LED_MODE_OFF)
 		return LED_OFF;
 
-	switch (value & 0x27) {
-	case 0x24:
+	switch (FIELD_GET(KBD_LED_BRIGHTNESS_MASK, value)) {
+	case KBD_LED_BRIGHTNESS_FULL:
 		return LED_FULL;
-	case 0x22:
+	case KBD_LED_BRIGHTNESS_HALF:
 		return LED_HALF;
 	default:
 		return LED_OFF;