Re: Kernel Display and Video API Consolidation mini-summit at ELC 2012 - Notes

[James Simmons <jsimmons@infradead.org>]

> > Imo we should ditch this - fb accel doesn't belong into the kernel. Even
> > on hw that still has a blitter for easy 2d accel without a complete 3d
> > state setup necessary, it's not worth it. Chris Wilson from our team once
> > played around with implementing fb accel in the kernel (i915 hw still has
> > a blitter engine in the latest generations). He quickly noticed that to
> > have decent speed, competitive with s/w rendering by the cpu he needs the
> > entire batch and buffer management stuff from userspace. And to really
> > beat the cpu, you need even more magic.
> > 
> > If you want fast 2d accel, use something like cairo.
> 
> Our conclusion on this is that we should not expose an explicit 2D 
> acceleration API at the kernel level. If really needed, hardware 2D 
> acceleration could be implemented as a DRM device to handle memory management, 
> commands ring setup, synchronization, ... but I'm not even sure if that's 
> worth it. I might not have conveyed it well in my notes.

Fbcon scrolling at be painful at HD or better modes. Fbcon needs 3 
possible accels; copyarea, imageblit, and fillrect. The first two could be 
hooked from the TTM layer. Its something I plan to experiment to see if 
its worth it.