[coreboot] Geode db800 vs Wyse S50

Peter Stuge peter at stuge.se
Tue May 25 16:11:53 CEST 2010

Oliver Schinagl wrote:
> > You can do some things also without VSA. VSA is used to create
> > virtual PCI devices for among other things sound and graphics.
> > However, a native graphics driver such as the one in libpayload or
> > xf86-video-geode may not need VSA to drive the graphics hardware.
> I suppose I won't even need VSA? I intend on booting Linux only; so
> as long as that works, i'd be happy?

I think Linux will need VSA to be happy though.

> How does this virtual PCI device thing work?


The VSA blob installs a System Management Mode handler which traps
instructions that normally access PCI hardware, and they are instead
handled by the VSA code, which responds like PCI hardware would.

> Or what should I imagine in that area? My mind draws a blank. I just
> know that usually your video chips is connected to the PCI bus. How
> would this all work on a virtual PCI bus?

The Geode is a different architecture, it uses a different bus called
GeodeLink, and provides PCI compatibility on top of that.

Drivers that understand GeodeLink directly (such as the X graphics
driver) do not need the PCI compat stuff.

> If using seabios; would I need the VSA to draw the boot menu
> selection screen (assuming there exists such a thing even :)

Actually it's even worse. You need a VGA BIOS for the CPU, and I
don't know if there is a free one available. There was a GSoC project
last year to create one, and there were patches that worked on Geode
LX, but I'm not sure about the status on GX2.

Those patches were for the SeaBIOS VGA BIOS "subproject" and I don't
know for sure if VSA is needed, but I would guess that it is.


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