VGA arbitration: API proposal

[Egbert Eich]

Jon Smirl writes:
 > 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?

Nope. There is no such thing as a secondary address range for all 
VGA registers. For the CRT regs there is a monochrome and a 
color address range. That's not sufficient, though. It allows
you to share a monochrome (MDA) and a color video card.

Egbert.