[Intel-gfx] Is MI_FLUSH_ENABLE bit 12?

[Daniel Vetter]

On Tue, Dec 06, 2011 at 12:21:02PM -0800, Jesse Barnes wrote:
> On Tue, 06 Dec 2011 11:56:07 -0800
> Eric Anholt <eric at anholt.net> wrote:
> > > It's one of those "been there forever" bits.  A comment wouldn't hurt,
> > > but we should also put in a doc change request (in fact I think I did
> > > that but it went into a black hole).
> >
> > Well, by "been there forever", you mean "introduced in:
> >
> > commit a69ffdbfcba8eabf2ca9d384b578e6f28b339c61
> > Author: Zhenyu Wang <zhenyuw at linux.intel.com>
> > Date:   Mon Aug 30 16:12:42 2010 +0800
> >
> >     drm/i915: Enable MI_FLUSH on Sandybridge
> >
> >     MI_FLUSH is being deprecated, but still available on Sandybridge.
> >     Make sure it's enabled as userspace still uses MI_FLUSH.
> >
> >     Signed-off-by: Zhenyu Wang <zhenyuw at linux.intel.com>
> >     Cc: stable at kernel.org
> >     Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>"
> >
> > It should be removed on Ironlake, and fixed to be 12 on SNB or just
> > removed.
>
> No, "fixed to be 12" would just encourage people to still try it and
> break their machines.  We can safely remove it now that we don't use it
> anywhere.  And we can fix the docs so that if people do want to mess
> with it they won't try bit 12.

If userspace ever relied on this being enabled we cannot just disable it
now - it would break the kernel<->userspace abi on snb. You have to wait
for 5-10 years, eternity or until the last userspace using this
disappeared, whichever comes first ;-)

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