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

To: <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] beginnings of allowing more than the basic 80x25 VGA screen resolution
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Mon, 04 Jul 2005 02:35:55 -0600
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>> As far as I know, not only the VGA driver does not do any mode
>> switching, even the VESA one doesn't (because the protected mode
>> interface doesn't cover the mode switching functions as far as I
>> remember). Only the video board specific frame buffer drivers are
>> to switch modes, and the bad thing (for me personally) is that even
>> 2.6.12 there still is no (64-bit) support for the i915 chipset. So
>> continue to be required to live with the video mode that XEN 'sets'
>> prior to loading dom0, and short of it supporting a VESA console my
>> first minimal attempt was to at least increase (and propagate) the
>> to the maximum possible without significant changes.
>That's a pain. Maybe we can find a simple example somewhere of setting

>video mode via protect-mode VBE calls. I see that this functionality
>missing from the kernel drivers -- it's all done in a monstrous 
>real-mode assembly file. Any video card we care about these days
>support VBE 2.0/3.0 I think, and those interfaces don;t require you to

>be runnign in real mode.

At least for VBE 2.0 such code can't exist; the protected mode
interface only covers
- setting the memory window
- setting the display start
- setting the primary palette
and I don't think 3.0 significantly extended that interface. The
assumption here is that any program wishing to use this is going to set
up its video mode once and for all in real mode, and then only require
some limited support in setting certain output-related things.


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