On Mon, 10 Dec 2018 at 19:33, Christoph Hellwig <hch@xxxxxx> wrote: > > On Mon, Dec 10, 2018 at 05:04:46PM +0000, Rui Salvaterra wrote: > > Hi, Christoph and Ben, > > > > It just came to my mind (and this is most likely a stupid question, > > but still)… Is there any possibility of these changes having an > > (positive) effect on the long-standing problem of Power Mac machines > > with AGP graphics cards (which have to be limited to PCI transfers, > > otherwise they'll hang, due to coherence issues)? If so, I have a G4 > > machine where I'd gladly test them. > > These patches themselves are not going to affect that directly. > But IFF the problem really is that the AGP needs to be treated as not > cache coherent (I have no idea if that is true) the generic direct > mapping code has full support for a per-device coherent flag, so > support for a non-coherent AGP slot could be implemented relatively > simply. Thanks for the insight, Christoph. Well, the problem[1] is real, and it's been known for a long time, though I can't be sure if it's *only* a coherence issue. If someone who knows the hardware manages to cook up a patch (as hacky is it may be), I'll definitely fire up old my G4 laptop to test it! :) [1] https://bugs.freedesktop.org/show_bug.cgi?id=95017
