Re: [PATCH] platform/x86/amd: Introduce Halo Box RGB LED driver

[Armin Wolf <W_Armin@gmx.de>]

Am 27.04.26 um 04:25 schrieb Mario Limonciello (AMD):

> The Halo Box features an RGB LED light bar that can be controlled
> through WMI methods to display any color combination.
>
> The driver exposes the LED through the LED multicolor subsystem,
> allowing userspace to control RGB values via sysfs:
>    /sys/class/leds/amd_halo:rgb:light_bar/multi_intensity
>    /sys/class/leds/amd_halo:rgb:light_bar/brightness
>
> Hardware interface:
> - Three separate RGB channels (Red, Green, Blue)
> - Each channel controlled via individual WMI method calls
> - Value range: 0-100 (matching hardware range directly)
>
> Co-developed-by: Leo.Lin@amd.com
> Signed-off-by: Leo.Lin@amd.com
> Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
> ---
>   MAINTAINERS                             |   7 +
>   drivers/platform/x86/amd/Kconfig        |  12 +
>   drivers/platform/x86/amd/Makefile       |   1 +
>   drivers/platform/x86/amd/amd_halo_led.c | 375 ++++++++++++++++++++++++
>   4 files changed, 395 insertions(+)
>   create mode 100644 drivers/platform/x86/amd/amd_halo_led.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2fb1c75afd163..c35b654a65041 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -1124,6 +1124,13 @@ F:	drivers/char/hw_random/geode-rng.c
>   F:	drivers/crypto/geode*
>   F:	drivers/video/fbdev/geode/
>   
> +AMD HALO BOX RGB LED DRIVER
> +M:	Mario Limonciello (AMD) <superm1@kernel.org>
> +R:	Leo Lin <Leo.Lin@amd.com>
> +L:	platform-driver-x86@vger.kernel.org
> +S:	Supported
> +F:	drivers/platform/x86/amd/amd_halo_led.c
> +
>   AMD HSMP DRIVER
>   M:	Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com>
>   R:	Carlos Bilbao <carlos.bilbao@kernel.org>
> diff --git a/drivers/platform/x86/amd/Kconfig b/drivers/platform/x86/amd/Kconfig
> index b813f92653686..d642386938055 100644
> --- a/drivers/platform/x86/amd/Kconfig
> +++ b/drivers/platform/x86/amd/Kconfig
> @@ -34,6 +34,18 @@ config AMD_WBRF
>   	  This mechanism will only be activated on platforms that advertise a
>   	  need for it.
>   
> +config AMD_HALO_LED
> +	tristate "AMD Halo Box RGB LED Driver"
> +	depends on ACPI_WMI
> +	select LEDS_CLASS_MULTICOLOR

I do not think selecting whole subsystems is a good idea. Consider changing this
to "depends on".

> +	help
> +	  This driver provides RGB LED control for AMD Halo Box devices
> +	  through the LED multicolor subsystem. The Halo Box light bar can
> +	  be controlled via sysfs to display any RGB color combination.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called amd_halo_led.
> +
>   config AMD_ISP_PLATFORM
>   	tristate "AMD ISP4 platform driver"
>   	depends on I2C && X86_64 && ACPI
> diff --git a/drivers/platform/x86/amd/Makefile b/drivers/platform/x86/amd/Makefile
> index f6ff0c837f345..2f467dbbfc8a3 100644
> --- a/drivers/platform/x86/amd/Makefile
> +++ b/drivers/platform/x86/amd/Makefile
> @@ -10,5 +10,6 @@ obj-$(CONFIG_AMD_PMC)		+= pmc/
>   obj-$(CONFIG_AMD_HSMP)		+= hsmp/
>   obj-$(CONFIG_AMD_PMF)		+= pmf/
>   obj-$(CONFIG_AMD_WBRF)		+= wbrf.o
> +obj-$(CONFIG_AMD_HALO_LED)	+= amd_halo_led.o
>   obj-$(CONFIG_AMD_ISP_PLATFORM)	+= amd_isp4.o
>   obj-$(CONFIG_AMD_HFI)		+= hfi/
> diff --git a/drivers/platform/x86/amd/amd_halo_led.c b/drivers/platform/x86/amd/amd_halo_led.c
> new file mode 100644
> index 0000000000000..01b4583ca70f3
> --- /dev/null
> +++ b/drivers/platform/x86/amd/amd_halo_led.c
> @@ -0,0 +1,375 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * AMD Halo Box RGB LED Driver
> + *
> + * Copyright (C) 2026 Advanced Micro Devices, Inc.
> + *
> + * This driver provides RGB LED control for AMD Halo Box devices through
> + * the LED multicolor subsystem. The Halo Box light bar can be controlled
> + * via sysfs to display any RGB color combination.
> + */
> +
> +#include <linux/acpi.h>
> +#include <linux/led-class-multicolor.h>
> +#include <linux/leds.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/wmi.h>
> +
> +#define AMD_HALO_GUID "081E747B-E028-4232-AF24-EAAEAB2B1E86"
> +
> +/* WMI method IDs from MOF */
> +#define AMD_HALO_WMI_GET_LIGHTBAR	0x01
> +#define AMD_HALO_WMI_SET_LIGHTBAR	0x02
> +#define AMD_HALO_WMI_TURN_ON		0x03
> +#define AMD_HALO_WMI_TURN_OFF		0x04

Hi,

can you use an enum for that? Also i suggest you create a small piece of documentation
under Documetnation/wmi/devices so that future developers understand how this WMI device
is supposed to work.

> +
> +/* Channel selectors for Arg0 */
> +#define AMD_HALO_CHANNEL_RED		0x01
> +#define AMD_HALO_CHANNEL_GREEN		0x02
> +#define AMD_HALO_CHANNEL_BLUE		0x03
> +
> +/* Status codes from spec */
> +#define AMD_HALO_STATUS_SUCCESS		0x0000
> +#define AMD_HALO_STATUS_INVALID_PARAM	0xFFFD
> +
> +/* Brightness uses 0-100 range */
> +#define AMD_HALO_MAX_HW_BRIGHTNESS		100
> +
> +/**
> + * struct amd_halo_led_data - Driver private data
> + * @wdev: WMI device pointer
> + * @led_mc: LED multicolor class device
> + * @subled_info: RGB channel information
> + * @lock: Mutex to protect WMI calls
> + */
> +struct amd_halo_led_data {
> +	struct wmi_device *wdev;
> +	struct led_classdev_mc led_mc;
> +	struct mc_subled subled_info[3];
> +	struct mutex lock;	/* Protects WMI method calls */
> +};
> +
> +struct amd_halo_wmi_args {
> +	u32 arg0;
> +	u32 arg1;
> +};
> +
> +/**
> + * amd_halo_wmi_set_channel - Set a single RGB channel value
> + * @wdev: WMI device pointer
> + * @channel: Channel selector (1=Red, 2=Green, 3=Blue)
> + * @brightness: brightness to set (0-100)
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +static int amd_halo_wmi_set_channel(struct wmi_device *wdev, u32 channel,
> +				    u32 brightness)
> +{
> +	struct amd_halo_wmi_args args = {
> +		.arg0 = channel,
> +		.arg1 = brightness,
> +	};
> +	const struct acpi_buffer input = {
> +		.length = sizeof(args),
> +		.pointer = &args,
> +	};
> +	struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
> +	union acpi_object *obj;
> +	acpi_status status;
> +	u16 result_status;
> +	int ret = 0;
> +
> +	/* Validate input per spec */
> +	if (channel < AMD_HALO_CHANNEL_RED ||
> +	    channel > AMD_HALO_CHANNEL_BLUE ||
> +	    brightness > AMD_HALO_MAX_HW_BRIGHTNESS)
> +		return -EINVAL;
> +
> +	status = wmidev_evaluate_method(wdev, 0, AMD_HALO_WMI_SET_LIGHTBAR,
> +					&input, &output);

Please use wmidev_invoke_method() instead. Take a look at Documentation/wmi/driver-development-guide.rst
on how to use this new API.

> +	if (ACPI_FAILURE(status)) {
> +		dev_err(&wdev->dev, "SetLightBar failed: %s\n",
> +			acpi_format_exception(status));

Please remove dev_err() here, the return value is enough.

> +		return -EIO;
> +	}
> +
> +	/* Parse return buffer per spec: Bytes[0:1] = Status */
> +	obj = output.pointer;
> +	if (!obj || obj->type != ACPI_TYPE_BUFFER || obj->buffer.length < 2 ||
> +	    !obj->buffer.pointer) {
> +		dev_err(&wdev->dev, "Invalid return buffer\n");
> +		ret = -EIO;
> +		goto out;
> +	}
> +
> +	result_status = obj->buffer.pointer[0] |
> +			(obj->buffer.pointer[1] << 8);
> +	if (result_status != AMD_HALO_STATUS_SUCCESS) {
> +		dev_err(&wdev->dev, "WMI returned error: 0x%04x\n",
> +			result_status);
> +		ret = -EIO;

Please model result_status as a __le16 and perform a pointer cast
from the buffer (after the size check of course).

> +	}
> +
> +out:
> +	kfree(output.pointer);
> +	return ret;
> +}
> +
> +/**
> + * amd_halo_wmi_get_channel - Get a single RGB channel value
> + * @wdev: WMI device pointer
> + * @channel: Channel selector (1=Red, 2=Green, 3=Blue)
> + * @value: Pointer to store the read value
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +static int amd_halo_wmi_get_channel(struct wmi_device *wdev, u32 channel,
> +				    u8 *value)
> +{
> +	struct amd_halo_wmi_args args = {
> +		.arg0 = channel,
> +		.arg1 = 0,  /* Reserved */
> +	};
> +	const struct acpi_buffer input = {
> +		.length = sizeof(args),
> +		.pointer = &args,
> +	};
> +	struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
> +	union acpi_object *obj;
> +	acpi_status status;
> +	u16 result_status;
> +	int ret = 0;
> +
> +	if (channel < AMD_HALO_CHANNEL_RED || channel > AMD_HALO_CHANNEL_BLUE)
> +		return -EINVAL;
> +
> +	status = wmidev_evaluate_method(wdev, 0, AMD_HALO_WMI_GET_LIGHTBAR,
> +					&input, &output);
> +	if (ACPI_FAILURE(status))
> +		return -EIO;

Same as above.

> +
> +	obj = output.pointer;
> +	if (!obj || obj->type != ACPI_TYPE_BUFFER || obj->buffer.length < 3 ||
> +	    !obj->buffer.pointer) {
> +		ret = -EIO;
> +		goto out;
> +	}
> +
> +	result_status = obj->buffer.pointer[0] |
> +			(obj->buffer.pointer[1] << 8);
> +	if (result_status != AMD_HALO_STATUS_SUCCESS) {
> +		ret = -EIO;
> +		goto out;
> +	}

Same as above.

> +
> +	/* Value returned in Byte[2] per spec */
> +	*value = obj->buffer.pointer[2];
> +
> +out:
> +	kfree(output.pointer);
> +	return ret;
> +}
> +
> +/**
> + * amd_halo_wmi_turn_off - Turn off all LED channels
> + * @wdev: WMI device pointer
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +static int amd_halo_wmi_turn_off(struct wmi_device *wdev)
> +{
> +	struct amd_halo_wmi_args args = {
> +		.arg0 = 0,
> +		.arg1 = 0,
> +	};
> +	const struct acpi_buffer input = {
> +		.length = sizeof(args),
> +		.pointer = &args,
> +	};
> +	struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
> +	acpi_status status;
> +
> +	status = wmidev_evaluate_method(wdev, 0, AMD_HALO_WMI_TURN_OFF,
> +					&input, &output);
> +	kfree(output.pointer);

This looks strange, does the WMI method return any data? If yes then please perform error
checking, otherwise use wmidev_invoke_procedure().

> +
> +	return ACPI_FAILURE(status) ? -EIO : 0;
> +}
> +
> +/**
> + * amd_halo_brightness_set - Set LED brightness and color
> + * @cdev: LED class device
> + * @brightness: Brightness value (0 = off, >0 = on with color)
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +static int amd_halo_brightness_set(struct led_classdev *cdev,
> +				   enum led_brightness brightness)
> +{
> +	struct led_classdev_mc *mc_cdev = lcdev_to_mccdev(cdev);
> +	struct amd_halo_led_data *data = container_of(mc_cdev,
> +						       struct amd_halo_led_data,
> +						       led_mc);
> +	u32 red_hw, green_hw, blue_hw;
> +	int ret;
> +
> +	guard(mutex)(&data->lock);
> +
> +	if (brightness == 0)
> +		return amd_halo_wmi_turn_off(data->wdev);

I suggest that you update the RGB color first, otherwise the LED will return wrong RGB values when
turned off.

> +
> +	led_mc_calc_color_components(mc_cdev, brightness);
> +	red_hw = mc_cdev->subled_info[0].brightness;
> +	green_hw = mc_cdev->subled_info[1].brightness;
> +	blue_hw = mc_cdev->subled_info[2].brightness;
> +
> +	/* Set each channel individually - 3 WMI calls required */
> +	ret = amd_halo_wmi_set_channel(data->wdev, AMD_HALO_CHANNEL_RED,
> +				       red_hw);
> +	if (ret)
> +		return ret;
> +
> +	ret = amd_halo_wmi_set_channel(data->wdev, AMD_HALO_CHANNEL_GREEN,
> +				       green_hw);
> +	if (ret)
> +		return ret;
> +
> +	return amd_halo_wmi_set_channel(data->wdev, AMD_HALO_CHANNEL_BLUE,
> +					blue_hw);
> +}
> +
> +/**
> + * amd_halo_brightness_get - Get current LED brightness state
> + * @cdev: LED class device
> + *
> + * Return: brightness last set by the user, or AMD_HALO_MAX_HW_BRIGHTNESS if
> + *         it was set by BIOS, or LED_OFF if all LEDs are off.
> + */
> +static enum led_brightness amd_halo_brightness_get(struct led_classdev *cdev)
> +{
> +	struct led_classdev_mc *mc_cdev = lcdev_to_mccdev(cdev);
> +	struct amd_halo_led_data *data = container_of(mc_cdev,
> +						       struct amd_halo_led_data,
> +						       led_mc);
> +	u8 red_hw = 0, green_hw = 0, blue_hw = 0;
> +	int ret;
> +
> +	guard(mutex)(&data->lock);
> +
> +	/* Read each channel */
> +	ret = amd_halo_wmi_get_channel(data->wdev, AMD_HALO_CHANNEL_RED,
> +				       &red_hw);
> +	if (ret)
> +		return LED_OFF;
> +
> +	ret = amd_halo_wmi_get_channel(data->wdev, AMD_HALO_CHANNEL_GREEN,
> +				       &green_hw);
> +	if (ret)
> +		return LED_OFF;
> +
> +	ret = amd_halo_wmi_get_channel(data->wdev, AMD_HALO_CHANNEL_BLUE,
> +				       &blue_hw);
> +	if (ret)
> +		return LED_OFF;
> +
> +	if (mc_cdev->subled_info[0].brightness == red_hw
> +	    && mc_cdev->subled_info[1].brightness == green_hw
> +	    && mc_cdev->subled_info[2].brightness == blue_hw) {
> +		return cdev->brightness;
> +	}

I do not think that this is a good idea. Maybe you should initialize the brightness values
during probing and just not implement brightness_get at all as the hardware seems to have
no possibility to read the global brightness.

> +
> +	mc_cdev->subled_info[0].intensity = red_hw;
> +	mc_cdev->subled_info[1].intensity = green_hw;
> +	mc_cdev->subled_info[2].intensity = blue_hw;
> +
> +	return AMD_HALO_MAX_HW_BRIGHTNESS;
> +}
> +
> +/**
> + * amd_halo_color_set_default - Set LED to initial color and brightness
> + * @cdev: LED class device
> + *
> + * Sets all RGB channels to 20% intensity as an initial state.
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +static int amd_halo_color_set_default(struct led_classdev *cdev)
> +{
> +	struct led_classdev_mc *mc_cdev = lcdev_to_mccdev(cdev);
> +
> +	mc_cdev->subled_info[0].intensity = AMD_HALO_MAX_HW_BRIGHTNESS / 5;
> +	mc_cdev->subled_info[1].intensity = AMD_HALO_MAX_HW_BRIGHTNESS / 5;
> +	mc_cdev->subled_info[2].intensity = AMD_HALO_MAX_HW_BRIGHTNESS / 5;
> +
> +	return amd_halo_brightness_set(cdev, AMD_HALO_MAX_HW_BRIGHTNESS);

Please fold this into amd_halo_probe().

> +}
> +
> +/**
> + * amd_halo_probe - Driver probe function
> + * @wdev: WMI device
> + * @context: Context data (unused)
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +static int amd_halo_probe(struct wmi_device *wdev, const void *context)
> +{
> +	struct amd_halo_led_data *data;
> +	int ret;
> +
> +	data = devm_kzalloc(&wdev->dev, sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->wdev = wdev;
> +	mutex_init(&data->lock);
> +	dev_set_drvdata(&wdev->dev, data);
> +
> +	data->subled_info[0].color_index = LED_COLOR_ID_RED;
> +	data->subled_info[1].color_index = LED_COLOR_ID_GREEN;
> +	data->subled_info[2].color_index = LED_COLOR_ID_BLUE;
> +	data->subled_info[0].intensity = 0;
> +	data->subled_info[1].intensity = 0;
> +	data->subled_info[2].intensity = 0;
> +
> +	data->led_mc.led_cdev.name = "amd_halo:rgb:light_bar";

I think the lightbar could be viewed as a status LED, so "amd_halo:multicolor:status"
would be more suitable here. This would also mirror the uniwill-laptop driver.

> +	data->led_mc.led_cdev.brightness = AMD_HALO_MAX_HW_BRIGHTNESS;
> +	data->led_mc.led_cdev.max_brightness = AMD_HALO_MAX_HW_BRIGHTNESS;
> +	data->led_mc.led_cdev.brightness_set_blocking = amd_halo_brightness_set;
> +	data->led_mc.led_cdev.brightness_get = amd_halo_brightness_get;
> +	data->led_mc.led_cdev.flags = LED_CORE_SUSPENDRESUME | LED_RETAIN_AT_SHUTDOWN;
> +	data->led_mc.num_colors = 3;

Please use ARRAY_SIZE() here.

> +	data->led_mc.subled_info = data->subled_info;
> +
> +	ret = devm_led_classdev_multicolor_register(&wdev->dev, &data->led_mc);
> +	if (ret)
> +		return dev_err_probe(&wdev->dev, ret,
> +				     "Failed to register multicolor LED\n");

Why not using devm_led_classdev_multicolor_register_ext() here?

> +
> +	ret = amd_halo_color_set_default(&data->led_mc.led_cdev);

Please do this _before_ registering the LED device, otherwise userspace applications might
have already set a RGB color themself. Failing to set the initial hardware state should also
result in probe failure.

> +	if (ret)
> +		dev_warn(&wdev->dev, "Unable to set default LED intensity through WMI: %d\n", ret);
> +
> +	return 0;
> +}
> +
> +static const struct wmi_device_id amd_halo_id_table[] = {
> +	{ .guid_string = AMD_HALO_GUID },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(wmi, amd_halo_id_table);
> +
> +static struct wmi_driver amd_halo_driver = {
> +	.driver = {
> +		.name = "amd_halo_led",
> +	},
> +	.id_table = amd_halo_id_table,

Please set .no_singleton = true here.

Otherwise the driver looks good to me.

Thanks,
Armin Wolf

> +	.probe = amd_halo_probe,
> +};
> +
> +module_wmi_driver(amd_halo_driver);
> +
> +MODULE_AUTHOR("Mario Limonciello (AMD) <superm1@kernel.org>");
> +MODULE_AUTHOR("Leo Lin <Leo.Lin@amd.com>");
> +MODULE_DESCRIPTION("AMD Halo Box RGB LED Control Driver");
> +MODULE_LICENSE("GPL");