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

[Alex Deucher]

On Mon, Jun 17, 2013 at 12:07 PM, Adam Jackson <ajax at redhat.com> wrote:
> On Mon, 2013-06-17 at 11:04 -0400, Alex Deucher wrote:
>> On Mon, Jun 17, 2013 at 10:06 AM, Adam Jackson <ajax at redhat.com> wrote:
>> > At least on an IBM Power 720, this check passes, but several piglit
>> > tests will reliably trigger GPU resets due to the ring buffer pointers
>> > not being updated.  There's probably a better way to limit this to just
>> > affected machines though.
>>
>> What radeon chips are you seeing this on?  wb is more or less required
>> on r6xx and newer and I'm not sure those generations will even work
>> properly without writeback enabled these days.  We force it to always
>> be enabled on APUs and NI and newer asics.  With KMS, wb encompasses
>> more than just rptr writeback; it covers pretty much everything
>> involving the GPU writing any status information to memory.
>
> FirePro 2270, at least.  Booting with no_wb=1, piglit runs to completion
> with no GPU resets or IB submission failures.  Booting without no_wb,
> the following piglits go from pass to fail, all complaining that the
> kernel rejected CS:

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.

Alex