Multi-monitor (xinerama/mergefb) support in RandR

Alex Deucher alexdeucher at
Wed Jun 28 12:18:44 PDT 2006

On 6/28/06, Alex Deucher <alexdeucher at> wrote:
> On 6/28/06, Benjamin Herrenschmidt <benh at> 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).

Actually, what about just extending the exa memory manager to get rid
of the concept of offscreen, just flag certain pixmaps as "scanout
buffers" and then just allocated the buffers from the offscreen
manager. then turning on the second head is just a matter of
exaAllocateMem().  You'd have to re-init the DRI stuff though as your
locations may change, but back/depth/texture buffers could all just be
ExaAllocate() calls as well.  I guess we are back to the old FB
manager problem...


> Alex

More information about the xorg mailing list