Hi,
On Wed, May 11, 2011 at 03:59:24AM -0500, Clark, Rob wrote:
I've been thinking a bit about this.. we have something similar with TILER on OMAP4 (which is sort of a system-wide IOMMU that can also do tiling), where you wouldn't see the same data if you just remapped the same physical pages elsewhere. (I think GART's can in some cases untile to provide the CPU with a sensible view of tiled surfaces, which would somehow be similar... but disclaimer: I'm not coming from a desktop graphics background so please correct me as needed ;-)). At least in the OMAP4 case, any other hw block in the system can all read thru the remapped TILER address and continue to see a untiled layout of the pixel data.
Yes, you're correct: most desktop hardware that I know of can expose different views of surfaces, including untiled views of tiled surfaces. Hence how we've managed to this day to avoid introducing a tiled rasteriser in X, despite most target hardware requiring tiling internally. ;)
I believe new(er) NVIDIA hardware both enforces tiling (at least in some cases), and is not able to expose untiled views, though.
Cheers, Daniel