linux-kernel - Re: Future handling of complex RGB devices on Linux v2

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Date: Thu, 22 Feb 2024 12:38:07 +0100
From: Gregor Riepl <onitake@...il.com>
To: Werner Sembach <wse@...edocomputers.com>
Cc: 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,
 Pavel Machek <pavel@....cz>, Hans de Goede <hdegoede@...hat.com>
Subject: Re: Future handling of complex RGB devices on Linux v2

> This certainly is the most KISS approach. This proposal
> in essence is just an arbitrary command multiplexer /
> demultiplexer and ioctls already are exactly that.
> 
> With the added advantage of being able to directly use
> pass the vendor-cmd-specific struct to the ioctl instead
> of having to first embed it in some other struct.

There's also the question of how much complexity needs to remain in the 
kernel, if vendor-specific ioctls are made available.

Does every vendor driver implement a complex mapping to hardware 
registers? What about drivers that basically implement no mapping at all 
and simply forward all data to the hardware without any checking? The 
latter case would match Pavel's concerns, although I don't see how this 
is any different from the situation today, where userspace talks 
directly to the hardware via libusb etc.

To be honest, I think the kernel shouldn't include too much high-level 
complexity. If there is a desire to implement a generic display device 
on top of the RGB device, this should be a configurable service running 
in user space. The kernel should provide an interface to expose this 
emulated display as a "real" display to applications - unless this can 
also be done entirely in user space in a generic way.