KMS and TTM questions

Thomas Hellstrom thomas at
Tue Oct 4 09:54:46 PDT 2011

On 10/04/2011 01:07 AM, Alan Cox wrote:
>> Thats fine as long as you don't want to do acceleration or object
>> migration between GTT
>> and VRAM type memory. Now I expect when you give out this advice you
> Yes but the VIA doesn't if I recall correctly have any 'VRAM type memory'.
> It's all effectively in the GART with the 'stolen' pages preloaded into
> the translation tables by the BIOS at vga init time.

VRAM memory (at least on the older unichromes) is taken from on-board 
RAM and set up by the BIOS, and from a device programmer's point of view 
works like a discrete card VRAM, and is *not* part of the GART.

On some devices (K8M800) , the VRAM pages could be accessed by the CPU 
directly at the top of VRAM, which was substantially faster.

There is a fully functional unichrome DRM on top of TTM, that together 
with the 3D driver in mesa's openchrome branch worked like a charm (even 
outperformed Intel's i965 with identical CPU at the time).
Problem was that it was not backwards compatible with via's old drm.

It should serve as a good starting point though, if I can remember where 
I put it....


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