adding randr 1.2 support to a video driver

Alex Deucher alexdeucher at
Sun Jul 22 16:05:27 PDT 2007

On 7/21/07, Mathieu Lacage <Mathieu.Lacage at> wrote:
> hi,
> So, I did my homework and read through a bunch of video specifications
> and driver code to figure out how things are done. I see, for example,
> that the intel video driver now does not use VBE anymore to configure
> the cards's video mode and accesses directly the VGA or DVI LVDS busses
> to fetch the EDID information from the connected monitor/panel. Is it
> required to do something similar to implement randr support ? i.e.,
> could I just use VBE directly to get the EDID information for randr
> support ? I fear that VBE is not going to work once the server is
> started: am I right ?

You can do a vbe based randr implementation.  You'd just have to hook
in the vbe calls in the right places in the randr modesetting and
detect code.  There are no problems using vbe in the running server.
several drivers do it already.  Generally direct register banging is
preferred as it gives you better control and doesn't require real mode
bios calls.


> Mathieu
> On Sat, 2007-07-14 at 16:01 +0200, Mathieu Lacage wrote:
> > hi,
> >
> > I wonder if there is any kind of documentation on what a driver is
> > expected to do to provide randr 1.2 support. Even a very basic outline
> > of what needs to be done and how would be immensely useful.
> >
> > Mathieu
> >
> > _______________________________________________
> > xorg mailing list
> > xorg at
> >
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