[Intel-gfx] [PATCH 18/43] drm/i915: fix swizzle detection for gen3

[Chris Wilson]

On Wed, 14 Dec 2011 13:57:15 +0100, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> It looks like the desktop variants of i915 and i945 also have the DCC
> register to control dram channel interleave and cpu side bit6
> swizzling.
> 
> Unfortunately internal Cspec/ConfigDB documentation for these ancient chips
> have already been dropped and there seem to be no archives. Also
> somebody thought the swizzling behaviour is surely a worthy secret to
> keep and redacted any mention of these fields from the published Intel
> datasheets.
> 
> I suspect the hw engineers were really proud of the page coloring
> they've achieved in their first dual channel dram controller with
> bit17 - after all Bspec explains in great length the optimal layout of
> page frame numbers modulo 4 for the color and depth buffers, too.
> Later on when they've started to work on VT-d they shamefully
> discoverd their stupidity and tried to cover the tracks ...
> 
> Tested-by: Daniel Vetter <daniel.vetter at ffwll.ch> (i915g)
> Tested-by: Pavel Ondračka <pavel.ondracka at email.cz> (i945g)
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=42625
> Cc: stable at kernel.org
> Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

It doesn't appear to have broken any of my machines, but I'm going to
qualify that to only the laptops I've look at the output of as well as
having run i-g-t!
Tested-by: Chris Wilson <chris at chris-wilson.co.uk> (no changes on 855gm, pnv, gm45, ilk, snb)
-Chris


-- 
Chris Wilson, Intel Open Source Technology Centre