On Mon, 10 Dec 2018 at 20:49, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> wrote: > [snip] > > AGP is a gigantic nightmare :-) It's not just cache coherency issues > (some implementations are coherent, some aren't, Apple's is ... weird). > > Apple has all sort of bugs, and Darwin source code only sheds light on > some of them. Some implementation can only read, not write I think, for > example. There are issues with transfers crossing some boundaries I > beleive, but it's all unclear. > > Apple makes this work with a combination of hacks in the AGP "driver" > and the closed source GPU driver, which we don't see. > > I have given up trying to make that stuff work reliably a decade ago :) > > Cheers, > Ben. That's what I was afraid of… what a mess. At least now I have a definitive answer from one of the original authors of the code, thanks a lot, Ben. :) I have an unresearched belief that AGP support was hacked in the Mac series as an afterthought (weren't they supposed to be PCI/PCI-X only?), and your explanation surely seems to corroborate. :/
