Multi-monitor (xinerama/mergefb) support in RandR

[Alex Deucher]

On 6/28/06, Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:
> On Tue, 2006-06-27 at 23:07 +0200, Keith Packard wrote:
> > Eric and I are busy figuring out how to handle multiple monitor hot plug
> > with X and have a fairly simple plan.
> >
> > Multi-screen X basically sucks, so few people are really excited about
> > using it. Xinerama sucks in the DIX implementation because it makes
> > things slow and bloated. Mergefb mostly rocks; fast, small and even DRI
> > continues to work right.
>
>  +/- the limitations of some 3d engines for too big screens... I don't
> know if/how that can be handled...
>

Iterating across the framebuffer in coordinate sized chucks in the 3D
driver. The 2d engine will also have this problem due to the
limitations of XAA.  for this to work properly, drivers really need
EXA support, otherwise you'll have to add hacks to re-base the 2d
engine if you are outside your coordinate limits.

Come to think of it, even EXA may be problematic.  the visible screen
may no longer be solely at offset 0 if you have particularly big
multi-head desktop.  Also, for things like tiling, you may need
multiple tiled surfaces to handle big desktops (one per crtc
potentially).

Alex