Kernel support for graphics cards

[olafBuddenhagen at gmx.net]

Hi,

> > Why not? Kernels have drivers for every other piece for hardware, so
> > what's stopping them from having gfx drivers?
> 
> i'd argue "why not" as well. but the kernel developers disagree.

Well, they disagree on what? Putting complete graphics drivers into the
kernel? Well, that's understandable, considering their size/complexity.

Or disagree on putting only the actual graphics hardware access into the
kernel? I doubt they do. Note that with fbdev and DRM and stuff, they
already have most of it anyways. What's lacking is a consistent and
complete framework, for doing all graphics hardware access in a single
(board-specific) driver, and exporting the functionality to userspace
through a well designed interface.

> and i woudl say that doing a gfx driver in userspace definitely makes
> for easier development & debugging. :) also it means for better
> performance characteristics of an OS if the gfx subsystem is doing
> some heavy software fallbacks - the driver can be pre-empted
> trivially... like any process... because... it is a process! :)

That sounds much like a microkernel approach :-) Personally, I'm a
strong proponent of microkernel designs. However, that's not what we are
dealing with here.

Microkernel systems are designed for doing almost everything in
userspace from the ground up, and provide the necessary facilities to do
it sanely. Monolithic kernels do not. Kernel space is the designated
place for hardware access on monolithic systems, and any attempt to
break this rule -- unless factually turning it into a microkernel design
-- will inevitably result in a mess like the one we have with graphics
drivers today.

Note however that for ease of development, a minimal kernel driver
providing robust multiplexing, and the complex userspace drivers no
longer able to do anything harmful, will be a *great* improvement over
the current situation, where the user space drivers are allowed to muck
about with anything and lock up your graphics system or worse.

-antrik-