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Date: Thu, 18 Nov 2010 11:11:49 +0200
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] Re: [PATCH] spice: add qxl device
Message-ID: <20101118091149.GY7948@redhat.com>
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>, qemu-devel@nongnu.org

On Thu, Nov 18, 2010 at 11:03:21AM +0200, Michael S. Tsirkin wrote:
> On Thu, Nov 18, 2010 at 10:09:35AM +0200, Gleb Natapov wrote:
> > On Wed, Nov 17, 2010 at 08:00:08PM +0200, Michael S. Tsirkin wrote:
> > > > >>  If so: does qemu
> > > > >>emulate this correctly?
> > > > >
> > > > >It mostly does.
> > > > 
> > > > I doubt it actually enables/disables the legacy vga ports.
> > > 
> > > I'll check when I have the time. We can fix it if it doesn't,
> > > 
> > So many guests (all of them?) just assume that vga ports and
> > framebuffer is there.
> 
> Why do you think they disable io memory then?
> 
Who and how and when disables io memory? Some guests are designed to run
even on old ISA machines that have no way to disable anything. The
device is just there.

This is the same with IDE ports. BIOS "knows" legacy ISA ports and just
program them into PCI IO bars to be nice.

> > So what "fixing" this will buy us?
> 
> Besides spec compliancy, you mean?  Ability to support multiple VGA
> cards. That's how it works I think: BIOS enables IO on the primary
> VGA device only.
> 
What spec defines hot-plug for primary VGA adapter? Our BIOS should support
-M isa machine too. There is no way to disable VGA or even check if it
is present there.

--
			Gleb.