RE: [PATCH v2] platform/x86/amd: Introduce Halo Box RGB LED driver

[Lin, Leo]

AMD General

> -----Original Message-----
> From: S-k, Shyam-sundar <Shyam-sundar.S-k@xxxxxxx>
> Sent: Wednesday, May 6, 2026 12:34 PM
> To: Lin, Leo <Leo.Lin@xxxxxxx>; Hans de Goede <hansg@xxxxxxxxxx>; Ilpo
> Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>; Mario Limonciello (AMD)
> <superm1@xxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; platform-driver-x86@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2] platform/x86/amd: Introduce Halo Box RGB LED driver
>
>
>
> On 5/4/2026 19:51, Yo-Jung Leo Lin (AMD) wrote:
> > [You don't often get email from leo.lin@xxxxxxx. Learn why this is
> > important at https://aka.ms/LearnAboutSenderIdentification ]
> >
> > 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:multicolor:status/multi_intensity
> >   /sys/class/leds/amd_halo:multicolor:status/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: Mario Limonciello (AMD) <superm1@xxxxxxxxxx>
> > Signed-off-by: Mario Limonciello (AMD) <superm1@xxxxxxxxxx>
> > Signed-off-by: Yo-Jung Leo Lin (AMD) <Leo.Lin@xxxxxxx>
> > ---
> > v1 -> v2:
> > - Fix Kconfig dependencies
> > - Remove amd_halo_wmi_turn_off(). Handle the case where brightness=0 with
> the
> >   same logic where brightness != 0
> > - Remove the brightness_get callback, because currently there isn't a
> >   well-defined global bightness in hardware. Note that the sysfs brightness
> >   stil works. It just caches the value last set.
> > - Convert to wmidev_invoke_method()
> > - Convert to ARRAY_SIZE()
> > - Convert some macros to enum
> > - Convert to devm_led_classdev_multicolor_register_ext()
> > - Rename sysfs path to amd_halo:multicolor:status
> > - Fold default LED colors setting in probe, before registration
> > - Add no_singleton option
> > - Make default RGB values into macros and adjust their values
> > ---
> >  MAINTAINERS                             |   7 +
> >  drivers/platform/x86/amd/Kconfig        |  11 ++
> >  drivers/platform/x86/amd/Makefile       |   1 +
> >  drivers/platform/x86/amd/amd_halo_led.c | 222
> > ++++++++++++++++++++++++++++++++
> >  4 files changed, 241 insertions(+)
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS index
> > c871acf2179c..464bd4d16461 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@xxxxxxxxxx>
> > +R:     Yo-Jung Leo Lin (AMD) <Leo.Lin@xxxxxxx>
> > +L:     platform-driver-x86@xxxxxxxxxxxxxxx
> > +S:     Supported
> > +F:     drivers/platform/x86/amd/amd_halo_led.c
> > +
> >  AMD HSMP DRIVER
> >  M:     Naveen Krishna Chatradhi <naveenkrishna.chatradhi@xxxxxxx>
> >  R:     Carlos Bilbao <carlos.bilbao@xxxxxxxxxx>
> > diff --git a/drivers/platform/x86/amd/Kconfig
> > b/drivers/platform/x86/amd/Kconfig
> > index b813f9265368..a1a74ef6c859 100644
> > --- a/drivers/platform/x86/amd/Kconfig
> > +++ b/drivers/platform/x86/amd/Kconfig
> > @@ -34,6 +34,17 @@ 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 && LEDS_CLASS_MULTICOLOR
> > +       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 f6ff0c837f34..2f467dbbfc8a 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 000000000000..12188571c7d9
> > --- /dev/null
> > +++ b/drivers/platform/x86/amd/amd_halo_led.c
> > @@ -0,0 +1,222 @@
> > +// 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/unaligned.h> #include <linux/wmi.h>
> > +
> > +#define AMD_HALO_GUID "081E747B-E028-4232-AF24-EAAEAB2B1E86"
> > +
> > +/* WMI method IDs from MOF */
> > +enum {
> > +       AMD_HALO_WMI_GET_LIGHTBAR = 0x01,
> > +       AMD_HALO_WMI_SET_LIGHTBAR,
> > +       AMD_HALO_WMI_TURN_ON,
> > +       AMD_HALO_WMI_TURN_OFF
>
> v2 has turn_off calls removed but the enums are not updated.
>
> AMD_HALO_WMI_TURN_ON/OFF values are not in use.

Will remove this in the next version

>
> > +};
> > +
> > +/* Channel selectors for Arg0 */
> > +enum {
> > +       AMD_HALO_CHANNEL_RED = 0x01,
> > +       AMD_HALO_CHANNEL_GREEN,
> > +       AMD_HALO_CHANNEL_BLUE
> > +};
> > +
> > +/* Status codes from spec */
> > +#define AMD_HALO_STATUS_SUCCESS                0x0000
> > +#define AMD_HALO_STATUS_INVALID_PARAM  0xFFFD
>
> This macro is not used. Please see below for more comments.

Ok, will (see below) keep this macro and do what you suggested.

>
> > +
> > +/* Brightness uses 0-100 range */
> > +#define AMD_HALO_MAX_HW_BRIGHTNESS     100
> > +
> > +/* Default RGB brightness */
> > +#define AMD_HALO_DEFAULT_RED           50
> > +#define AMD_HALO_DEFAULT_GREEN         30
> > +#define AMD_HALO_DEFAULT_BLUE          30
>
> 50/30/30 means a reddish-orange on the startup. Intentional? Should it be just
> 50/50/50 to look white?

It is intentional. They are tuned this way to compensate the color-filtering from the materials of the chassis. This is actually much closer to white than the values might appear to be at first look.

>
> > +
> > +/**
> > + * 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,
> > +       };
> > +       struct wmi_buffer input = {
> > +               .length = sizeof(args),
> > +               .data = &args,
> > +       };
> > +       struct wmi_buffer output = { 0 };
> > +       u16 result_status;
> > +       int ret;
> > +
> > +       /* Validate input per spec */
> > +       if (channel < AMD_HALO_CHANNEL_RED ||
> > +           channel > AMD_HALO_CHANNEL_BLUE ||
> > +           brightness > AMD_HALO_MAX_HW_BRIGHTNESS)
> > +               return -EINVAL;
> > +
> > +       ret = wmidev_invoke_method(wdev, 0, AMD_HALO_WMI_SET_LIGHTBAR,
> > +                                       &input, &output, sizeof(result_status));
> > +       if (ret)
> > +               return ret;
> > +
> > +       /* Return buffer per spec: Bytes[0:1] = Status (little-endian) */
> > +       result_status = get_unaligned_le16(output.data);
> > +       ret = (result_status == AMD_HALO_STATUS_SUCCESS) ? 0 : -EIO;
>
> AMD_HALO_STATUS_INVALID_PARAM macro usage could be something like this?
>
> if (result_status == AMD_HALO_STATUS_SUCCESS)
>     ret = 0;
> else if (result_status == AMD_HALO_STATUS_INVALID_PARAM)
>     ret = -EINVAL;
> else
>     ret = -EIO
>
> if no, the macro can be entirely dropped.

Will keep the macro and do this in the next version.

>
> > +
> > +       kfree(output.data);
> > +       return ret;
> > +}
> > +
> > +/**
> > + * amd_halo_brightness_set - Set LED brightness and color
> > + * @cdev: LED class device
> > + * @brightness: Brightness value
> > + *
> > + * 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);
> > +
> > +       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);
>
> what if one of the above set_channel fails? 3 things I can think of:
>
> - Restore previous state on failure, or
> - Accept partial updates (current behavior), or
> - Add a comment documenting this is intentional

Not sure if it's a good idea to use the same (already failing) WMI method to recover the WMI error here, but I guess it's probably better than not recovering it at all. Will add the recovery logic in the next version.

>
> > +}
> > +
> > +/**
> > + * 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 led_init_data led_init_data = {
> > +               .devicename = "amd_halo",
> > +               .default_label = "multicolor:" LED_FUNCTION_STATUS,
> > +               .devname_mandatory = true
> > +       };
> > +       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 = AMD_HALO_DEFAULT_RED;
> > +       data->subled_info[1].intensity = AMD_HALO_DEFAULT_GREEN;
> > +       data->subled_info[2].intensity = AMD_HALO_DEFAULT_BLUE;
> > +
> > +       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.flags = LED_CORE_SUSPENDRESUME |
> > + LED_RETAIN_AT_SHUTDOWN;
>
> Are these suspend/resume flags required?
>
> Does the hardware retain LED state across suspend/resume, or does the LED core
> need to restore it?

BIOS may change LED color during suspend, so this has to be restored after a resume.

>
> > +       data->led_mc.num_colors = ARRAY_SIZE(data->subled_info);
> > +       data->led_mc.subled_info = data->subled_info;
> > +
> > +       ret = amd_halo_brightness_set(&data->led_mc.led_cdev,
> > +                                     AMD_HALO_MAX_HW_BRIGHTNESS);
>
> brightness_set is called before the LED registration. Is this intentional?

It is intentional. For some reasons, the WMI values returned from BIOS won't be accurate after a cold boot, so set them to some known values here.

>
> > +       if (ret)
> > +               return dev_err_probe(&wdev->dev, ret,
> > +                                    "Failed to set default LED
> > + colors\n");
> > +
> > +       ret = devm_led_classdev_multicolor_register_ext(&wdev->dev, &data-
> >led_mc,
> > +                                                       &led_init_data);
> > +       if (ret)
> > +               return dev_err_probe(&wdev->dev, ret,
> > +                                    "Failed to register multicolor LED\n");
> > +       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,
> > +       .probe = amd_halo_probe,
> > +       .no_singleton = true,
> > +};
> > +
> > +module_wmi_driver(amd_halo_driver);
> > +
> > +MODULE_AUTHOR("Mario Limonciello (AMD) <superm1@xxxxxxxxxx>");
> > +MODULE_AUTHOR("Leo Lin <Leo.Lin@xxxxxxx>");
> MODULE_DESCRIPTION("AMD
> > +Halo Box RGB LED Control Driver"); MODULE_LICENSE("GPL");
> >
> > ---
> > base-commit: 39704f00f747aba3144289870b5fd8ac230a9aaf
> > change-id: 20260429-halo-leds-v2-plus-722c8083afe8
> >
> > Best regards,
> > --
> > Yo-Jung Leo Lin (AMD) <leo.lin@xxxxxxx>
> >
> >