[Intel-gfx] [PATCH] drm/i915: Re-enable mt forcewake check for IVB

[Takashi Iwai]

At Thu, 15 Nov 2012 21:22:41 +0100,
Takashi Iwai wrote:
> 
> At Thu, 15 Nov 2012 21:07:33 +0100,
> Daniel Vetter wrote:
> > 
> > On Thu, Nov 15, 2012 at 6:03 PM, Takashi Iwai <tiwai at suse.de> wrote:
> > > Some IVB machines seem to need non-MT forcewake.  Using MT forcewake
> > > on such machines result in broken or blank screens.
> > >
> > > Signed-off-by: Takashi Iwai <tiwai at suse.de>
> > > ---
> > > The commit 36ec8f877481449bdfa072e6adf2060869e2b970 triggered a
> > > regression on my test IVY laptops.  Instead of reverting the commit,
> > > I cooked a bit to make fitting only for IS_IVYBRIDGE().
> > 
> > Hm, that's rather bad since proper usage of DERRMR requires that we
> > enable rc6 on ivb, which is only really possible when we have
> > multi-threaded forcewake.
> 
> Hm, so just disabling RC6 doesn't suffice?
> 
> > Now I've thought that all production
> > machines have that enabled (it's something the bios should do), so the
> > big question: Is this a pre-production hw? If so, a bios upgrade
> > should fix it since historically we've killed pre-production
> > workarounds once the real hw ships, there are simply too many ...
> 
> Indeed a machine showing the issue is a prototype machine, but it's a
> product-ready unit, so I don't think CPU/GPU is different from the
> same model in the market.

It seems that I've looked at a lspci output on a wrong machine while
working remotely.  The machines showing the problem have CPU revisions
less than 8.

So, you are right, it must be specific to a pre-production CPU.
Assuming it being not in the market, I can live without that.
Time to throw away a crap :)

Sorry for the noise.


Takashi