[Xorg] The big multiconsole nasty

Jon Smirl jonsmirl at yahoo.com
Tue Jul 6 09:36:04 PDT 2004

--- John Dennis <jdennis at redhat.com> wrote:
> bus topology and that VGA routing is correct. Unlike the current

You can't make the assumptions about VGA routing. When secondary video
cards are reset by running their ROM, at the very least they enable
their VGA support. Sometimes they remap the bridges too.

We need kernel support for:
1) disabling all VGA devices
2) setting one VGA device active and get the bus routed to it
3) retrieving the board's VBIOS ROM.

This allow a user space reset program (they have to be user space since
they use VM86 mode) to disable all VGA devices, reset the card by
running the ROM, reenable the orginal VGA device.

#3 needs a special case. The kernel has to track which VGA device the
BIOS left active. When an app asks for the VBIOS ROM from this device,
you return the memory contents at C000:0. Some laptops compress the
VBIOS image of the primary adapter and this is where the uncompressed
version is stored. The kernel has to remember the boot device so that
if someone changes the active VGA device we will still know which
adapter the image at C000:0 belongs too.

Jon Smirl
jonsmirl at yahoo.com

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