Re: [PATCH 5/5] platform/x86: lg-laptop: Fix keyboard backlight support on LG Gram 16T90SP

[Ilpo Järvinen]

On Mon, 22 Jun 2026, Armin Wolf wrote:

> 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@xxxxxx>
> ---
>  drivers/platform/x86/lg-laptop.c | 47 ++++++++++++++++++++++++--------
>  1 file changed, 36 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/platform/x86/lg-laptop.c b/drivers/platform/x86/lg-laptop.c
> index d1b33a6b5206..22f8a6368f7c 100644
> --- a/drivers/platform/x86/lg-laptop.c
> +++ b/drivers/platform/x86/lg-laptop.c
> @@ -86,6 +86,18 @@ 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)

bits.h needed.

> +#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)
>  
> @@ -601,15 +613,25 @@ 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)
> @@ -621,13 +643,16 @@ 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;

Superb, I was already wanting to see this in patch 4 but had enough 
patience to look the subsequent patch first. Thanks for naming them!

-- 
 i.