Re: [PATCH 9/9] drm/i915: swizzling support for snb/ivb

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Nov 11, 2011 at 08:50:30AM -0800, Eric Anholt wrote:
> On Thu, 10 Nov 2011 14:18:07 +0100, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > We have to do this manually. Somebody had a Great Idea.
> > 
> > Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> People playing with this when not strictly required is scary to me.
> Manually swizzling was a world of hurt.  I got to play with things like
> "when the management engine is enabled, it carves out the top N MB of
> one of the dimms, and the corresponding N MB of the other dimm doesn't
> get swizzled, and you lose".

Looks like yet another patch series of mine that scares away people ...

Would this patch be less scary when we have a test that slurps in the
entire ram to quickly diagnose such issues? We can then either revert this
or fix up the detection to not enable swizzling in such cases.

Also the manually swizzling is a world of hurt argument is pretty void: Up
to very recent kernels we've advertised bit9 swizzling on snb+ without any
swizzling actually going on. So userspace clearly doesn't rely on this
anymore (the issue was caught by running the pread tests in i-g-t).

Also we already have a bug for gm45 which looks like a portion of ram
isn't swizzled:
https://bugs.freedesktop.org/show_bug.cgi?id=28813

-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48