ongoing writecombine on ppc

[Benjamin Herrenschmidt]

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.

_wc is only suitable for MMIO.

Cheers,
Ben.