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Re: [Xen-devel] beginnings of allowing more than the basic 80x25 VGAscre

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] beginnings of allowing more than the basic 80x25 VGAscreen resolution
From: Gerd Knorr <kraxel@xxxxxxx>
Date: Tue, 5 Jul 2005 15:42:50 +0200
Cc: xiaofeng.ling@xxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, Jan Beulich <JBeulich@xxxxxxxxxx>
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On Tue, Jul 05, 2005 at 02:28:27PM +0100, Keir Fraser wrote:
> On 5 Jul 2005, at 14:22, Jan Beulich wrote:
> >>GRUB has code for switching back into real mode to do bios calls. We
> >>could take that, plus video.S, and put them in Xen. Then add an info
> >>structure for passing video info up to domain0. It's pretty ugly, but
> >>I think there is no nice solution here.

Well, I'd simply leave that job completely to grub as it has to
deal with that anyway and the multiboot spec have fields to pass
on that info to the booted kernel.  Xen would simply take that
and pass it on to the Dom0 kernel, thats it.  And maybe adjust
it's own row/column counts in case it's vga text mode.

> >> Would we also need vesa/vga
> >>driver code from Linux for setting up font data in some graphics
> >modes?
> >
> >Yes that would clearly be necessary, but perhaps a much more
> >streamlined mechanism would do for XEN.
> If that's the case, I'm sure Gerd can point out the 'moving parts' that 
> we actually need to get basic text output working. I was hoping video.S 
> alone would be sufficient... :-)

Text mode is really simple, that is just another screen size
than 80x25, but completely identical otherwise.  Font stuff is
handled by bios and vga hardware, nothing to worry about here.

In graphics mode you simply have a linear frame buffer and
you'll have to do everything yourself.  Linux has compiled-in
fonts for that.  Quite alot of stuff from drivers/video would
be needed to get that going in xen, but I wouldn't even try to
make xen render text in graphics mode and leave that completely
to the dom0 kernel ...


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