VGA arbitration: API proposal

[Benjamin Herrenschmidt]

On Sun, 2005-03-06 at 16:31 -0500, Jon Smirl wrote:
> These are the two VGA address ranges
> 
> 02B0-02DF	Alternate VGA Video Display Adaptor assignment (secondary address)
> 03B0-03DF	EGA / VGA Video Display Adaptor, (Primary address)
> 
> Not sure yet how to control which one a VGA card responds to
> 
> This is a standard VGA register
> http://www.osdever.net/FreeVGA/vga/extreg.htm
> it can disable the RAM response and move some of the IO

Very interesting. If that RAM enable thing actually works, that mean
that we can pretty much restrict all chips to IO decoding. At least ATIs
and I think nVidias can completely be used without IOs (using only
MMIOs), that means we have a way to deal with those in any situation
provided they actually implement this "magic" bit.... Toggling the bit
itself requires VGA access of course ;)

Ben.