Status of VGA Arbiter and Legacy VGA I/O?

Tiago Vignatti vignatti at
Mon Nov 23 14:37:15 PST 2009

Dave Airlie wrote:
> On Fri, 2009-11-20 at 13:44 -0800, Mike Travis wrote:
>> Adam Jackson wrote:
>>> My understanding is, by default the VGA arbiter support code in X will
>>> assume the driver _does_ need VGA arbitration, unless the driver opts
>>> out of it, and will wrap device access for you.  So whatever extra setup
>>> your platform needs should Just Work if you hook it up to the
>>> arbitration grant in the kernel.

correct, but ...

> If you are using a kms supporting driver, its quite easy to remove it
> from VGA arbitration, radeon and intel in the kernel do it already,
> if you can turn off VGA decodes on the GPU then you can ask the 
> kernel to remove it from VGA arbitration.

... there's an unfinished part of the server API concerning the way 
non-kms driver could skip from VGA arbitration. The function 
xf86VGAarbiterDeviceDecodes is kind dumb now and should be used for such 
purpose. We should fix it :/



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