Is CIRRUS a suitable driver to convert to atomic mode-setting

[Gerd Hoffmann]

On Do, 2015-04-02 at 09:57 +0800, John Hunter wrote:
> Hi Daniel,
> Sorry to disturb you, I realized you are a busy man of the community.
> So I did some work before I email you.
> 
> 
> I submit my proposal as you suggest, convert the two virtual driver
> (CIRRUS 
> and BOCHS, if I remember it right) to atomic mode-setting.
> 
> 
> After talked with Martin Peres(the administrator of xorg on gsoc) and 
> Gerd Hoffmann (the author of VirtIO gpu driver), we got this question,
> is CIRRUS suitable to convert, as qemu using cirrus considered
> harmful.

Short background summary on the later for everybody involved:

cirrus emulates hardware from the 90ies which simply isn't up to todays
needs.  The two major issues:

 * It has very limited video memory.  The cirrus driver does swap
   framebuffers in and out of video memory because of that.  I suspect
   converting the driver to atomic modesetting will be either impossible
   or at least pretty difficult because of that.  The limited video
   memory also limits the available resolutions, cirrus can't do FullHD
   for example.
 * cirrus can run 1024x768 only at 24bpp (not 32bpp).  Which is rather
   unusual these days and cirrus has display issues in xorg because it
   takes code paths which are not really maintained & tested any more.

cirrus isn't the default vga any more in qemu version 2.2 & newer
because of these problems.

cheers,
  Gerd