Re: FB and MTRR
Geert Uytterhoeven (Geert.Uytterhoeven@cs.kuleuven.ac.be)
Wed, 5 Aug 1998 15:05:07 +0200 (CEST)
On Wed, 5 Aug 1998, Richard Gooch wrote:
> Geert Uytterhoeven writes:
> > On Wed, 5 Aug 1998, Richard Gooch wrote:
> > > Martin Mares writes:
> > > > > Isn't it a bad idea to touch the old VGA registers? I thought it was
> > > > > better to use the new PCI space registers (so you can support multiple
> > > > > heads)?
> > > >
> > > > Unfortunately, different PCI video cards have different register
> > > > addressing :(
> > >
> > > Sorry, I'm missing the significance of that. My point was that the old
> > > VGA registers mapped to < 1 MByte limit you to one card, so would it
> > > not be better to have the FB code access the registers mapped to the
> > > PCI space?
> >
> > Martin is right about this: mirros of the VGA registers in PCI
> > memory space are nonstandard and differ between different video
> > chipsets.
>
> Is this a problem because you couldn't then have a plain VGA driver?
Right. VGA relies on the legacy I/O stuff.
> If so now I finally understand the point. That then imples that the
> plain VGA/VESA driver can only ever support one card, whereas a
> chipset-specific driver can support multiple cards?
Right.
Greetings,
Geert
--
Geert Uytterhoeven Geert.Uytterhoeven@cs.kuleuven.ac.be
Wavelets, Linux/{m68k~Amiga,PPC~CHRP} http://www.cs.kuleuven.ac.be/~geert/
Department of Computer Science -- Katholieke Universiteit Leuven -- Belgium
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