Intel framebuffer compression & tiling update

[Alan Cox]

> > The compression is line based, so if any line (or part of a line) is 
> > modified either during or after compression, it won't be scanned out 
> > from the compressed buffer, the GPU will use the uncompressed version 
> > instead.  Likewise, if a line hasn't been modified since the last pass, 
> > it won't be re-compressed; the per-line status is tracked in the 
> > compressed line length buffer (the "compressed ll" line the memory 
> > layout dump in the server log).
> 
> Ah, ok. That makes sense. Thanks for the explanation.

There is a good explanation of this in the Nat Semi Geode
CS5530 documentation btw, as that was the chip which invented this
technique and Cyrix were the original patent holders on it.