On Sat, 19 Mar 2011 12:20:24 +0100 Geert Uytterhoeven geert@linux-m68k.org wrote:
As noone responded to my question in http://www.spinics.net/lists/dri-devel/msg08851.html (yes, it was a bit hidden in a thread), I'm asking it here again (and also on the Wayland mailing list).
Basically I'm still puzzled about this KMS thing. If the name "Kernel Mode Setting" covers it, then how does it compare to plain fbdev? Just additional frame buffer memory management? Also, some people may remember we did have kernel messages (e.g. oops, panic) on graphical consoles with fbdev, until people started not liking them showing up on their X desktops...
We support panic these days as well, but people still don't like seeing them. :)
The DRM KMS APIs provide everything fbdev provides, plus memory management, a way to expose acceleration (via GEM or TTM), and a way to manage multiple outputs reasonably.
Furthermore, everybody states that "future desktop" (that's http://wayland.freedesktop.org/) will require KMS drivers. How do/will we handle this on dumb frame buffers? It's not like we can't do "advanced" things like compositing using the CPU. Transparency may stretch it a bit on lower end CPUs, but you don't always need that.
There's nothing in DRM that precludes doing simple fbdev-like drivers as well, though for many embedded uses I wouldn't expect it to provide a whole lot of benefit.