https://bugzilla.kernel.org/show_bug.cgi?id=19002

--- Comment #21 from Alex Deucher alexdeucher@gmail.com 2010-12-14 21:17:59 --- (In reply to comment #19)

2. No AGP fast-write here at all. AFAIK it's a chipset errata on AMD 8xxx.

It's buggy on all boards. We don't enable it at all with kms.

3. 256 MB AGP aperture, half of which is of course reserved for the AGPGART

IOMMU on the AMD 8xxx chipset. The BIOS allows larger (upto 1GB, which happens to be video memory size as well), but that was a reasonably late addition to the BIOS (256 was the previous limit), and for whatever reason I couldn't get it to work in testing, so I've stuck with 256 MB (128 MB of it AGPGART IOMMU), which /does/ work.

BTW, /should/ a larger aperture work? Given that half of it's AGGART IOMMU, should larger == better? I've not tested larger recently, maybe it works now?

Bigger isn't necessarily better, it just means more pages can be mapped into the gart. We default to 512 MB on non-AGP systems.

4. dmesg says AGP v3 device in 8x mode. Years ago I had problems with 8x and

had to use 4x max, but last I tried, 4x and 8x worked but 1x and 2x were broken.

AGP v3 devices only support 4x and 8x modes.