linux-kernel - Re: Implement per-key keyboard backlight as auxdisplay?

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Message-ID: <49f12cc1-2dce-43b3-addf-b0fdb7df8fdb@tuxedocomputers.com>
Date: Fri, 29 Dec 2023 20:13:44 +0100
From: Werner Sembach <wse@...edocomputers.com>
To: Hans de Goede <hdegoede@...hat.com>, Pavel Machek <pavel@....cz>,
 Jani Nikula <jani.nikula@...ux.intel.com>, jikos@...nel.org,
 Jelle van der Waa <jelle@...aa.nl>
Cc: Lee Jones <lee@...nel.org>, linux-kernel@...r.kernel.org,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, linux-input@...r.kernel.org,
 ojeda@...nel.org, linux-leds@...r.kernel.org
Subject: Re: Implement per-key keyboard backlight as auxdisplay?

Hi Hans & the others,

[snip]
> I also stumbled across a new Problem:
>
> We have an upcoming device that has a per-key keyboard backlight, but does the 
> control completely via a wmi/acpi interface. So no usable hidraw here for a 
> potential userspace driver implementation ...
>
> So a quick summary for the ideas floating in this thread so far:
>
> 1. Expand leds interface allowing arbitrary modes with semi arbitrary optional 
> attributes:
>
>     - Pro:
>
>         - Still offers all default attributes for use with UPower
>
>         - Fairly simple to implement from the preexisting codebase
>
>         - Could be implemented for all (to me) known internal keyboard backlights
>
>     - Con:
>
>         - Violates the simplicity paradigm of the leds interface (e.g. with 
> this one leds entry controls possible multiple leds)
>
> 2. Implement per-key keyboards as auxdisplay
>
>     - Pro:
>
>         - Already has a concept for led positions
>
>         - Is conceptually closer to "multiple leds forming a singular entity"
>
>     - Con:
>
>         - No preexisting UPower support
>
>         - No concept for special hardware lighting modes
>
>         - No support for arbitrary led outlines yet (e.g. ISO style enter-key)
>
> 3. Implement in input subsystem
>
>     - Pro:
>
>         - Preexisting concept for keys and key purpose
>
>     - Con:
>
>         - Not in scope for subsystem
>
>         - No other preexisting light infrastructure
>
> 4. Implement a simple leds driver only supporting a small subset of the 
> capabilities and make it disable-able for a userspace driver to take over
>
>     - Pro:
>
>         - Most simple to implement basic support
>
>         - In scope for led subsystem simplicity paradigm
>
>     - Con:
>
>         - Not all built in keyboard backlights can be implemented in a 
> userspace only driver
>
> Kind Regards,
>
> Werner

Just a gentle bump and request for comments again. 4. would be better then 
nothing but it is not a universal future proof solution so I'm hesitant to put 
work into it even though it would be the simplest driver. I still tend towards 
1. as the leds interface already got expanded once with the multicolor stuff.

The only other way I see would be to implement a platform driver with no 
standardized api or implement a complete new api/subsystem from the ground up.

Kind Regards,

Werner