linux-kernel - Re: [PATCH 2/2] drm/i915: properly clflush pwrites to phys objects

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Message-ID: <20111129161652.GD5667@phenom.ffwll.local>
Date:	Tue, 29 Nov 2011 17:16:52 +0100
From:	Daniel Vetter <daniel@...ll.ch>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH 2/2] drm/i915: properly clflush pwrites to phys objects

On Tue, Nov 29, 2011 at 03:35:54PM +0000, Chris Wilson wrote:
> On Tue, 29 Nov 2011 16:09:29 +0100, Daniel Vetter <daniel.vetter@...ll.ch> wrote:
> > Usually results in (rare) cursor corruptions on platforms
> > requiring physically addressed cursors.
> 
> So the phys cursor pages are set to WC upon creation, are we just
> missing the mb()? Or more likely the CPUs don't have PAT and we are
> being lazy in not detecting the error.

Yes, on reconsidering the tested-by is from a pentium m, which has working
pat, and we do a wbinvd in the i8xx chipset flush, so I don't know anymore
how this patch actually works.

But it seems to indeed fix the issue for at least one reporter and cursor
update is about as far away from a perf critical path as possible, so who
cares about such minor quibbles, it works ;-)
-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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