PowerPC agpmode issues

[Boris Reinhard]

Definitely would have made sense for years, but could someone possibly look
into a proper solution?

Michel Dänzer <michel at daenzer.net> schrieb am Mo., 8. Feb. 2016 11:00:

> On 05.02.2016 11:47, Mike wrote:
> > Hi.
> > Managed to get the Radeon R300 running on mesa 11.1.1 with an old 2013
> > patch from Michel Dànzer, next problem is of course enabling agpmode,
> > running with pci-mode with radeon.agpmode=-1 works, but is of course
> > slow, and seems to load the cpu a lot.
> >
> > Upon initial investigation i could not initially believe agp could be
> > this this broken for this long, until i found this.
> >  "committed with Ben Skeggs on Feb 26, 2013"
> >
> https://github.com/DespairFactor/bullhead/commit/650e1203c11354ba84d69ba445abc0efcfe3890a
> >
> http://lxr.free-electrons.com/source/drivers/gpu/drm/nouveau/nouveau_agp.c?v=4.2
> > #ifdef __powerpc__
> > /* Disable AGP by default on all PowerPC machines for
> > * now -- At least some UniNorth-2 AGP bridges are
> > * known to be broken: DMA from the host to the card
> > * works just fine, but writeback from the card to the
> > * host goes straight to memory untranslated bypassing
> > * the GATT somehow, making them quite painful to deal
> > * with...
> > */
> > if (nouveau_agpmode == -1)
> > return false;
> > #endif
> >
> >  and now later this:
> >
> https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/nouveau/nvkm/subdev/pci/agp.c
> > #ifdef __powerpc__
> > /* Disable AGP by default on all PowerPC machines for now -- At
> > * least some UniNorth-2 AGP bridges are known to be broken:
> > * DMA from the host to the card works just fine, but writeback
> > * from the card to the host goes straight to memory
> > * untranslated bypassing that GATT somehow, making them quite
> > * painful to deal with...
> > */
> > mode = 0;
> > #endif
> >
> > All seems to point to serious issues had around the time of change to
> > ums to kms and a serious regression hitting the linux kernel? No?
>
> Not really. UMS was just using a static GART mapping, whereas KMS is
> dynamically binding pages into the GART as needed. Apparently, older
> revisions of UniNorth have trouble with the latter. I think it would
> make sense to change radeon.agpmode to default to -1 on powerpc as well.
> Any takers?
>
>
> --
> Earthling Michel Dänzer               |               http://www.amd.com
> Libre software enthusiast             |             Mesa and X developer
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