[RFC] Remove AGP support from Radeon/Nouveau/TTM

[Rui Salvaterra]

On Tue, 12 May 2020 at 17:38, Daniel Vetter <daniel at ffwll.ch> 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… :)