ongoing writecombine on ppc

[Benjamin Herrenschmidt]

On Fri, 2015-10-02 at 14:53 +1000, Dave Airlie wrote:
> On 2 October 2015 at 14:45, Benjamin Herrenschmidt
> <benh at kernel.crashing.org> wrote:
> > On Fri, 2015-10-02 at 14:42 +1000, Dave Airlie wrote:
> > > I don't think we resolved this the last time we talked about it,
> > > 
> > > but radeon writecombine maps fail hard on ppc, I think all the
> > > fixes
> > > either did something bad to AGP systems or weren't liked.
> > > 
> > > My patch attached just fixes radeon, which is where I'm still
> > > seeing
> > > the issue.
> > 
> > Yes, you MUST NOT set the flags of system memory to anything other
> > than
> > fully cachable on any cache coherent powerpc machine. This should
> > be
> > bolted into the DRM core imho.
> > 
> 
> Except you guys screwed up and allowed AGP to exist on Power, and 
> that requires it.

Well, Apple did :-) Yes, AGP should never have existed in the first
place, I think that's a given :)

> So we have to keep the AGP trapdoor in place, and at the moment only
> the drivers know if they are AGP, hence why I had to add this in the 
> driver instead of in the drm core.
Cheers,
Ben.