linux-kernel - Re: In kernel virtual HID devices (was Future handling of complex RGB devices on Linux v3)

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Message-ID: <0c025223-9eeb-44dd-97a0-d7b6de28d90d@tuxedocomputers.com>
Date: Wed, 24 Jul 2024 23:08:32 +0200
From: Werner Sembach <wse@...edocomputers.com>
To: Pavel Machek <pavel@....cz>
Cc: Benjamin Tissoires <bentiss@...nel.org>,
 Hans de Goede <hdegoede@...hat.com>, Lee Jones <lee@...nel.org>,
 jikos@...nel.org, linux-kernel@...r.kernel.org,
 Jelle van der Waa <jelle@...aa.nl>,
 Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 linux-input@...r.kernel.org, ojeda@...nel.org, linux-leds@...r.kernel.org,
 Gregor Riepl <onitake@...il.com>
Subject: Re: In kernel virtual HID devices (was Future handling of complex RGB
 devices on Linux v3)

Hi

Am 24.07.24 um 19:36 schrieb Pavel Machek:
> Hi!
>
>>> IMO working with the HID LampArray is the way forward. So I would
>>> suggest to convert any non-HID RGB "LED display" that we are talking
>>> about as a HID LampArray device through `hid_allocate_device()` in the
>>> kernel. Basically what you are suggesting Hans. It's just that you don't
>>> need a formal transport layer, just a child device that happens to be
>>> HID.
>>>
>>> The next question IMO is: do we want the kernel to handle such
>>> machinery? Wouldn't it be simpler to just export the HID device and let
>>> userspace talk to it through hidraw, like what OpenRGB does?
>> That's already part of my plan: The kernels main goal is to give devices a
>> LampArray interface that don't have one already (e.g. because they are no
>> HID devices to begin with).
>>
>> The actual handling of LampArray will happen in userspace.
>>
>> Exception is that maybe it could be useful to implement a small subset of
>> LampArray in a generic leds-subsystem driver for backwards compatibility to
>> userspace applications that only implement that (e.g. UPower). It would
>> treat the whole keyboard as a single led.

LampArray also gives the HID keycode, if applicable, for keyboard leds.

It's the InputBinding field in the LampAttributesResponseReport, see HID Usage 
Tables v1.5 -> 26.3 Lamp Attributes Report.

Kind regards,

Werner

(ps sorry for resend @pavel, hit reply instead of reply all the first time)

(pps resend a second time because Thunderbird did HTML e-mail)

> Are you sure LampArray is good-enough interface? OpenRGB exposes
> keycode-to-LED interface, how will that work with LampArray?
>
> Best regards,
> 								Pavel