Re: ongoing writecombine on ppc

From: Dave Airlie <airlied@gmail.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: ongoing writecombine on ppc
Date: Fri, 2 Oct 2015 14:53:11 +1000	[thread overview]
Message-ID: <CAPM=9txS0Oh+63GkjUURiQ8itNQhCuYgH79qaEsNz37kyRU+Eg@mail.gmail.com> (raw)
In-Reply-To: <1443761116.2828.64.camel@kernel.crashing.org>

On 2 October 2015 at 14:45, Benjamin Herrenschmidt
<benh@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.

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.

Dave.
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