multiseat

[Jesse Barnes]

On Thursday, July 28, 2005 7:52 am, Adam Jackson wrote:
> > Benh already has a working prototype of VGA arbitration for the
> > kernel. It was discussed at Kernel Summit this year.
>
> The arbitration idea is lovely but it assumes that the card gives a
> damn when you tell it not to decode the VGA space, and there are many
> video cards that will stick their fingers in their ears and go LA LA
> LA I CAN'T HEAR YOU when you try.  You could assert that those cards
> are broken, but that's sort of the point: hardware is broken and will
> actively defeat attempts to be used in a multiseat setup.

As a result, I think it's reasonable to limit multiseat setups to a sane 
subset of cards that X supports.  If a card needs the VGA registers to 
be enabled during runtime for use by the driver, it seems especially 
broken to me.

Other than that though, VGA registers should only need to be available 
for card posting--once that's done, VGA stuff shouldn't happen at all, 
right?  Can we do things like screen blanking without it though?

The unfortunate thing is that VGA routing is both dependent on the card 
behaving well (i.e. honoring the VGA_EN bit) and potentially 
programming host<->PCI or PCI<->PCI bridges correctly to route legacy 
VGA I/O accesses.  This is  obviously very bridge dependent, so the 
kernel needs bridge drivers that export sane programming interfaces.

Jesse