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

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Date: Thu, 18 Jan 2024 18:45:36 +0100
From: Pavel Machek <pavel@....cz>
To: Werner Sembach <wse@...edocomputers.com>
Cc: Hans de Goede <hdegoede@...hat.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>, jikos@...nel.org,
	Jelle van der Waa <jelle@...aa.nl>,
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	Lee Jones <lee@...nel.org>, linux-kernel@...r.kernel.org,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	linux-input@...r.kernel.org, ojeda@...nel.org,
	linux-leds@...r.kernel.org
Subject: Re: Implement per-key keyboard backlight as auxdisplay?

Hi!

> 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:

>     - Con:
> 
>         - Violates the simplicity paradigm of the leds interface (e.g. with
> this one leds entry controls possible multiple leds)

Let's not do this.

> 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 lightning modes
> 
>         - No support for arbitrary led outlines yet (e.g. ISO style enter-key)

Please do this one.

> 3. Implement in input subsystem
> 
>     - Pro:
> 
>         - Preexisting concept for keys and key purpose
> 
>     - Con:
> 
>         - Not in scope for subsystem
> 
>         - No other preexisting light infrastructure

Or negotiate with input people to do this.

> 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

No. Kernel should abstract this away.

Best regards,
									Pavel
-- 
People of Russia, stop Putin before his war on Ukraine escalates.

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