Re: Future handling of complex RGB devices on Linux v3

Werner Sembach
2024-03-20T18:45:53Z

Am 20.03.24 um 12:33 schrieb Werner Sembach:
>
> Am 20.03.24 um 12:16 schrieb Werner Sembach:
>> Hi Hans and the others,
>>
>> Am 22.02.24 um 14:14 schrieb Werner Sembach:
>>> Hi,
>>>
>>> Thanks everyone for the exhaustive feedback. And at least this thread is a
>>> good comprehesive reference for the future ^^.
>>>
>>> To recap the hopefully final UAPI for complex RGB lighting devices:
>>>
>>> - By default there is a singular /sys/class/leds/* entry that treats the
>>> device as if it was a single zone RGB keyboard backlight with no special
>>> effects.
>>>
>>> - There is an accompanying misc device with the sysfs attributes "name",
>>> "device_type",  "firmware_version_string", "serial_number" for device
>>> identification and "use_leds_uapi" that defaults to 1.
>>>
>>>     - If set to 0 the /sys/class/leds/* entry disappears. The driver should
>>> keep the last state the backlight was in active if possible.
>>>
>>>     - If set 1 it appears again. The driver should bring it back to a static
>>> 1 zone setting while avoiding flicker if possible.
>>>
>>> - If the device is not controllable by for example hidraw, the misc device
>>> might also implement additional ioctls or sysfs attributes to allow a more
>>> complex low level control for the keyboard backlight. This is will be a
>>> highly vendor specific UAPI.
>> So in the OpenRGB issue thread
>> https://learn.microsoft.com/en-us/windows-hardware/design/component-guidelines/dynamic-lighting-devices
>> aka HID LampArray was mentioned. I did dismiss it because I thought that is
>> only relevant for firmware, but I now stumbled upon the Virtual HID Framework
>> (VHF)
>> https://learn.microsoft.com/en-us/windows-hardware/drivers/hid/virtual-hid-framework--vhf-
>> and now I wonder if an equivalent exists for Linux? A quick search did not
>> yield any results for me.
> Is this what I have been searching for?
> https://docs.kernel.org/usb/gadget_hid.html
Nope is something different: http://www.linux-usb.org/gadget/
>>
>> If a virtual HID device is possible and the WMI interface can reasonably be
>> mapped to the LampArray API this might be the best starting point:
>>
>> - Implement a Virtual HID device with LampArray
>>
>> - Implement LampArray in OpenRGB
>>
>> - (Optional) Implement a generic LampArray leds subsystem driver that maps to
>> the single zone control and ads the use_leds_uapi sysfs switch to the virtual
>> HID device
>>
>> - (Optional) Implement vendor specific controls for
>> AutonomousMode/built-in-firmware-effects via custom HID commands
>>
>> - (Optional) Implement Virtual HID devices for actual HID devices that don't
>> support LampArray in firmware (Open question: How to prevent
>> userspace/OpenRGB from interacting with original HID when the virtual HID
>> device is not in AutonomousMode? How to associate the original and virtual
>> HID device to each other that userspace can easily recognize this relation?
>> Or is it possible to add virtual HID commands on top of a real HID device,
>> making it look exactly like the pure virtual devices for userspace?)
>>
>> The LampArray API hereby is made with the intention to be used for multi leds
>> devices, like per-key-backlight keyboards, unlike the leds UAPI. And it is
>> coming anyway with new RGB devices soon. So it would not conflict with a
>> "don't introduce unnecessary UAPI interfaces" principle. Are there any plans
>> already of Wrapping LampArray in some kind ioctl/sysfs API? Or just have it
>> used via hidraw? Or was there no discussion about it till now?
>>
>> Regards,
>>
>> Werner
>>
>>>
>>>     - The actual logic interacting with this low level UAPI is implemented
>>> by a userspace driver
>>>
>>> Implementation wise: For the creation of the misc device with the
>>> use_leds_uapi switch a helper function/macro might be useful? Wonder if it
>>> should go into leds.h, led-class-multicolor.h, or a new header file?
>>>
>>> - Out of my head it would look something like this:
>>>
>>> led_classdev_add_optional_misc_control(
>>>     struct led_classdev *led_cdev,
>>>     char* name,
>>>     char* device_type,
>>>     char* firmware_version_string,
>>>     char* serial_number,
>>>     void (*deregister_led)(struct led_classdev *led_cdev),
>>>     void (*reregister_led)(struct led_classdev *led_cdev))
>>>
>>> Let me know your thoughts and hopefully I can start implementing it soon for
>>> one of our devices.
>>>
>>> Kind regards,
>>>
>>> Werner Sembach
>>>