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Date: Wed, 20 Mar 2024 19:45:43 +0100
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Subject: Re: Future handling of complex RGB devices on Linux v3
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From: Werner Sembach <wse@tuxedocomputers.com>
To: Hans de Goede <hdegoede@redhat.com>
Cc: Lee Jones <lee@kernel.org>, jikos@kernel.org,
 linux-kernel@vger.kernel.org, Jelle van der Waa <jelle@vdwaa.nl>,
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 linux-input@vger.kernel.org, ojeda@kernel.org, linux-leds@vger.kernel.org,
 Pavel Machek <pavel@ucw.cz>, Gregor Riepl <onitake@gmail.com>
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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
>>>