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

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Date: Fri, 19 Jan 2024 21:22:57 +0100
From: Werner Sembach <wse@...edocomputers.com>
To: Pavel Machek <pavel@....cz>, Hans de Goede <hdegoede@...hat.com>
Cc: 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,

Am 19.01.24 um 21:15 schrieb Pavel Machek:
> Hi!
>
>>>> 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.
>> Ok, so based on the discussion so far and Pavel's feedback lets try to
>> design a custom userspace API for this. I do not believe that auxdisplay
>> is a good fit because:
> Ok, so lets call this a "display". These days, framebuffers and drm
> handles displays. My proposal is to use similar API as other displays.
>
>> So my proposal would be an ioctl interface (ioctl only no r/w)
>> using /dev/rgbkbd0 /dev/rgbkdb1, etc. registered as a misc chardev.
>>
>> For per key controllable rgb LEDs we need to discuss a coordinate
>> system. I propose using a fixed size of 16 rows of 64 keys,
>> so 64x16 in standard WxH notation.
>>
>> And then storing RGB in separate bytes, so userspace will then
>> always send a buffer of 192 bytes per line (64x3) x 14 rows
>> = 3072 bytes. With the kernel driver ignoring parts of
>> the buffer where there are no actual keys.
> That's really really weird interface. If you are doing RGB888 64x14,
> lets make it a ... display? :-).
>
> ioctl always sending 3072 bytes is really a hack.
>
> Small displays exist and are quite common, surely we'd handle this as
> a display:
> https://pajenicko.cz/displeje/graficky-oled-displej-0-66-64x48-i2c-bily-wemos-d1-mini
> It is 64x48.
>
> And then there's this:
> https://pajenicko.cz/displeje/maticovy-8x8-led-displej-s-radicem-max7219
> and this:
> https://pajenicko.cz/displeje/maticovy-8x32-led-displej-s-radicem-max7219
>
> One of them is 8x8.
>
> Surely those should be displays, too?

But what about a light bar with, lets say, 3 zones. Is that a 3x1 display?

And what about a mouse having lit mousebuttons and a single led light bar at the 
wrist: a 2x2 display, but one is thin but long and one is not used?

Regards,

Werner

>
> And yes, we'd probably want some extra ioctls on top, for example to
> map from input device to this and back, and maybe for various effects,
> too. And yes, I realize that display with holes in it and with some
> pixels bigger than others is weird, but it still looks like a display
> to me. (And phones have high-res displays with rounded corners and
> holes in them, so... we'll need to deal with weird displays anyway).
>
> Best regards,
> 								Pavel