Re: [PATCH] platform/x86: huawei-wmi: Add keyboard backlight support

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Mon, 26 Oct 2026, Cian Ruane wrote:

> The HWMI interface of the HUAWEI MateBook X Pro 2020 (MACHC-WAX9)
> exposes the keyboard backlight through the \GLIV and \SLIV methods of
> the WMAA dispatcher (MFID 2, SFID 6/7), with the level in byte 2 of the
> buffer. The EC stores the level doubled, so the three levels off/low/
> high are represented as 0, 2 and 4.
> 
> Register a "platform::kbd_backlight" LED class device with a maximum
> brightness of 2 so that userspace, e.g. UPower, can control it.
> 
> Changes made with the Fn+F3 hotkey are handled by the EC itself and
> are not reported to the OS on this model: no EC query or WMI event is
> generated. LED_BRIGHT_HW_CHANGED is therefore not set.
> 
> The level encoding has only been verified on this model, so enable the
> feature through a DMI quirk.
> 
> Tested on: HUAWEI MACHC-WAX9 (MateBook X Pro 2020), BIOS 1.05 and 1.26,
> Ubuntu 24.04 (kernel 6.8.0-147-generic, with this patch backported).
> 
> Signed-off-by: Cian Ruane <cian.ruane1@gmail.com>
> ---
>  drivers/platform/x86/huawei-wmi.c | 64 +++++++++++++++++++++++++++++++
>  1 file changed, 64 insertions(+)
> 
> diff --git a/drivers/platform/x86/huawei-wmi.c b/drivers/platform/x86/huawei-wmi.c
> index 96ee9a97c..8eafda8a1 100644
> --- a/drivers/platform/x86/huawei-wmi.c
> +++ b/drivers/platform/x86/huawei-wmi.c
> @@ -39,8 +39,14 @@ enum {
>  	FN_LOCK_GET			= 0x00000604, /* \GFRS */
>  	FN_LOCK_SET			= 0x00000704, /* \SFRS */
>  	MICMUTE_LED_SET			= 0x00000b04, /* \SMLS */
> +	KBD_BACKLIGHT_GET		= 0x00000602, /* \GLIV */
> +	KBD_BACKLIGHT_SET		= 0x00000702, /* \SLIV */
>  };
>  
> +/* The EC stores the keyboard backlight level doubled: off/low/high = 0/2/4. */
> +#define KBD_BACKLIGHT_MAX		2
> +#define KBD_BACKLIGHT_STEP		2
> +
>  union hwmi_arg {
>  	u64 cmd;
>  	u8 args[8];
> @@ -50,6 +56,7 @@ struct quirk_entry {
>  	bool battery_reset;
>  	bool ec_micmute;
>  	bool report_brightness;
> +	bool kbd_backlight;
>  };
>  
>  static struct quirk_entry *quirks;
> @@ -65,6 +72,7 @@ struct huawei_wmi {
>  
>  	struct huawei_wmi_debug debug;
>  	struct led_classdev cdev;
> +	struct led_classdev kbd_cdev;
>  	struct device *dev;
>  
>  	struct mutex wmi_lock;
> @@ -126,6 +134,10 @@ static struct quirk_entry quirk_matebook_x = {
>  	.report_brightness = true,
>  };
>  
> +static struct quirk_entry quirk_kbd_backlight = {
> +	.kbd_backlight = true,
> +};
> +
>  static const struct dmi_system_id huawei_quirks[] = {
>  	{
>  		.callback = dmi_matched,
> @@ -145,6 +157,15 @@ static const struct dmi_system_id huawei_quirks[] = {
>  		},
>  		.driver_data = &quirk_matebook_x
>  	},
> +	{
> +		.callback = dmi_matched,
> +		.ident = "Huawei MACHC-WAX9",
> +		.matches = {
> +			DMI_MATCH(DMI_SYS_VENDOR, "HUAWEI"),
> +			DMI_MATCH(DMI_PRODUCT_NAME, "MACHC-WAX9"),
> +		},
> +		.driver_data = &quirk_kbd_backlight
> +	},
>  	{  }
>  };
>  
> @@ -322,6 +343,48 @@ static void huawei_wmi_leds_setup(struct device *dev)
>  	devm_led_classdev_register(dev, &huawei->cdev);
>  }
>  
> +/* Keyboard backlight */
> +
> +static enum led_brightness huawei_wmi_kbd_backlight_get(struct led_classdev *led_cdev)
> +{
> +	u8 ret[0x100];

Generally, avoid using literals and use named defines for sizes, offsets, 
and values (and BIT()/GENMASK() for bitfields).

> +	if (huawei_wmi_cmd(KBD_BACKLIGHT_GET, ret, sizeof(ret)))
> +		return 0;
> +
> +	/* byte[0] = STAT, byte[2] = level as stored by the EC */
> +	return ret[2] / KBD_BACKLIGHT_STEP;
> +}
> +
> +static int huawei_wmi_kbd_backlight_set(struct led_classdev *led_cdev,
> +					enum led_brightness brightness)
> +{
> +	union hwmi_arg arg;
> +
> +	arg.cmd = KBD_BACKLIGHT_SET;
> +	arg.args[2] = brightness * KBD_BACKLIGHT_STEP;
> +
> +	return huawei_wmi_cmd(arg.cmd, NULL, 0);
> +}
> +
> +static void huawei_wmi_kbd_backlight_setup(struct device *dev)
> +{
> +	struct huawei_wmi *huawei = dev_get_drvdata(dev);
> +
> +	if (!quirks || !quirks->kbd_backlight)
> +		return;
> +
> +	if (huawei_wmi_cmd(KBD_BACKLIGHT_GET, NULL, 0))
> +		return;
> +
> +	huawei->kbd_cdev.name = "platform::kbd_backlight";
> +	huawei->kbd_cdev.max_brightness = KBD_BACKLIGHT_MAX;
> +	huawei->kbd_cdev.brightness_get = &huawei_wmi_kbd_backlight_get;
> +	huawei->kbd_cdev.brightness_set_blocking = &huawei_wmi_kbd_backlight_set;
> +
> +	devm_led_classdev_register(dev, &huawei->kbd_cdev);
> +}
> +
>  /* Battery protection */
>  
>  static int huawei_wmi_battery_get(int *start, int *end)
> @@ -915,6 +978,7 @@ static int huawei_wmi_probe(struct platform_device *pdev)
>  		mutex_init(&huawei_wmi->wmi_lock);
>  
>  		huawei_wmi_leds_setup(&pdev->dev);
> +		huawei_wmi_kbd_backlight_setup(&pdev->dev);
>  		huawei_wmi_fn_lock_setup(&pdev->dev);
>  		huawei_wmi_battery_setup(&pdev->dev);
>  		huawei_wmi_debugfs_setup(&pdev->dev);
> 
> base-commit: 9d3475065167197742b0882aff21cf8e78393277
> 

-- 
 i.