On Wed, 13 May 2020 at 04:21, Alex Deucher <alexdeucher@xxxxxxxxx> wrote: > > On Tue, May 12, 2020 at 1:02 PM Rui Salvaterra <rsalvaterra@xxxxxxxxx> wrote: > > > > On Tue, 12 May 2020 at 17:38, Daniel Vetter <daniel@xxxxxxxx> wrote: > > > > > > Otherwise all agree, agp is a mighty mess and essentially just > > > crapshot outside of x86. It kinda worked for the much more static > > > allocations for dri1, but with in-kernel memory managers all the cache > > > flushing issues showed up big time and it all fell to pieces. Plus a > > > lot of these host chipset back then where designed for the rather > > > static windows gpu managers, so even on x86 the coherency issues for > > > agp mode when used together with ttm or something else really dynamic > > > is pretty bad because the hw just doesn't really cope and has all > > > kinds of flushing troubles and races. I think the later agp chipsets > > > were better. > > > > That was rather insightful, thanks. I was starting to doubt my own > > memory, as I was almost sure I never had any hangs with AGP on PowerPC > > before KMS was a thing. But even on x86, I distinctly remember never > > being able to get sideband addressing working with any AGP cards, my > > system would randomly hang too. > > I'm starting to believe AGP was shoehorned into PCI the same way VLB > > was shoehorned into ISA (and for the same reason). History repeats > > itself… :) > > Pre-KMS, the kernel just allocated a static relatively small (e.g., 8 > MB) AGP buffer which never changed. In that case, things were > somewhat more reliable. This is why the AGP hw on Macs has issues I believe. It was designed and only tested around the one static early allocation, I'm not sure OSX ever did dynamic. When it went dynamic I think the AGP bits had some problems with coherency of the GART tables that we never figured out. Dave. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
