[PATCH] xfree86: use vgaarb only if X configures more than one card

Vignatti Tiago (Nokia-D/Helsinki) tiago.vignatti at nokia.com
Tue Sep 1 09:49:57 PDT 2009

On Tue, Sep 01, 2009 at 10:55:49AM +0200, ext Julien Cristau wrote:
> On Mon, Aug 31, 2009 at 20:39:21 +0300, Tiago Vignatti wrote:
> > X server still doesn't have support for video card hotplug. Therefore, if
> > the kernel returns more than one device but the X claims only one, then
> > give priority for what X is telling.
> > 
> Don't you still need the arbiter with multiple X servers, each claiming
> one card?

The thing is that we're assigning DRM drivers with GPUs which don't need to
use legacy VGA registers, and consequently don't need arbitration. On other
words, we're betting that we'll be able to turn off the legacy VGA registers
on all DRM drivers. Fair enough; in this case the linux still keeping the
correct number of cards that needs for the arbitration.

On the other hand, there are the miserables drivers that don't have the kernel
counter-part. In that case we're supposing that _all_ need the legacy VGA.
And I didn't seen so far an X-only driver (the miserables) that does _not_
need the legacy VGA registers to do int10, acpi, etc. So if this would be the
case then we'd have to implement some hook on userspace to notify the vga
arbiter's count on kernel (right now xf86VGAarbiterDeviceDecodes is forcing
mem and io decodes). But again, forget about that given that I didn't see such

Anyway, I was just trying to avoid all the X functions being wrapped by the
arbiter when I want one single-card X server with X-only driver in a machine
having more than one card. But eh, why someone would put more than one card in
a machine and not use some? Very dumb scenario.

So you're right Julien. I've realized that just after cooked the patch and was
thinking for a while :/ So just ignore my patch guys.

Thank you.

            Tiago, confusing even more the things

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