[PATCH] drm/radeon: Disable writeback by default on ppc

[Benjamin Herrenschmidt]

On Fri, 2013-11-08 at 11:43 -0200, Kleber Sacilotto de Souza wrote:
> On 11/07/2013 08:29 PM, Benjamin Herrenschmidt wrote:
> > On Mon, 2013-06-17 at 18:57 -0400, Alex Deucher wrote:
> >
> >> Weird.  I wonder if there is an issue with cache snoops on PPC.  We
> >> currently use the gart in cached mode (GPU snoops CPU cache) with
> >> cached pages.  I wonder if we need to use uncached pages on PPC.
> >
> > There is no such issue and no known bugs with DMA writes on those
> > PCIe host bridges (and they do get hammered pretty bad here).
> >
> > This needs further investigation by the lab/hw guys to find out what's
> > actually happening on the bus and the host bridge.
> >
> > Thadeu, Kleber: Jerome suggested writing a test case in userspace that
> > continuously writes to a spare scratch register (thus triggering the
> > corresponding writeback DMA) and checks the memory location to compare
> > the writeback value (using a debugfs file for example, or mmap).
> >
> 
> I can look into that.

Any news ?

Ben.

> 
> Thanks,
> 
> Kleber
> 
> > Can you guys do something like that ? Then we need the analyzer on
> > and/or the lab guys to look at the fabric trace & PHB trace.
> >
> > Ben.
> >
> >
> 
>