VGA arbitration: API proposal

[Benjamin Herrenschmidt]

On Sat, 2005-03-05 at 11:48 -0500, Jon Smirl wrote:
> On Sat, 05 Mar 2005 10:44:25 +1100, Benjamin Herrenschmidt
> <benh at kernel.crashing.org> wrote:
> >    This one would inform the arbitrer that your card is decoding VGA
> > accesses or not. It should be called by the driver, by default, the
> > arbitrer assumes all cards are decoding VGA addresses. I need to double
> > check what is needed for radeon to stop decoding VGA accesses, I'm not
> > 100% sure about that. CRTC_EXT_DISP_EN plus some other bit in DAC_CNTL
> > may be enough, but we should make sure of that. I think nVidia's can
> > remap the VGA IOs to some other place in PCI space with real decoding,
> > so they become a non-issue.
> 
> Doesn't VGA support both a primary and secondary address range? If we
> can't figure out how to completely shut off VGA could we map all of
> cards we aren't going to use on top of each other in the secondary
> address range and then ignore them?

Ok, that's more than my basic knowlege of VGA (that is I don't know
about this secondary address range thing). If we can map them all
together in some place nobody will access, it fixes the problem. But if
that was possible, why wouldn't things like XFree have done it already ?

Ben.