linux-kernel - Re: [git pull] drm fixes

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Message-ID: <20120227084520.548ea01b@jbarnes-desktop>
Date:	Mon, 27 Feb 2012 08:45:20 -0800
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Eugeni Dodonov <eugeni@...onov.net>
Cc:	Torsten Kaiser <just.for.lkml@...glemail.com>, DRI@...edesktop.org,
	linux-kernel@...r.kernel.org,
	mailing list <dri-devel@...ts.freedesktop.org>,
	Eugeni Dodonov <eugeni.dodonov@...el.com>
Subject: Re: [git pull] drm fixes

On Mon, 27 Feb 2012 13:33:53 -0300
Eugeni Dodonov <eugeni@...onov.net> wrote:

> On Mon, Feb 27, 2012 at 13:09, Jesse Barnes <jbarnes@...tuousgeek.org>wrote:
> 
> > On Thu, 23 Feb 2012 21:19:20 +0100
> > Torsten Kaiser <just.for.lkml@...glemail.com> wrote:
> >
> > > On Wed, Feb 22, 2012 at 8:56 PM, Dave Airlie <airlied@...ux.ie> wrote:
> > > > Eugeni Dodonov (4):
> > > >      drm/i915: gen7: implement rczunit workaround
> > > >      drm/i915: gen7: Implement an L3 caching workaround.
> > > >      drm/i915: gen7: work around a system hang on IVB
> > > >      drm/i915: do not enable RC6p on Sandy Bridge
> > >
> > > That last patch about RC6p looks wrong.
> > >
> > > It does:
> > >  GEN6_RC_CTL_RC6_ENABLE |
> > >                       (IS_GEN7(dev_priv->dev)) ? GEN6_RC_CTL_RC6p_ENABLE
> > : 0;
> > > But I think this was meant:
> > >  GEN6_RC_CTL_RC6_ENABLE |
> > >                       ((IS_GEN7(dev_priv->dev)) ?
> > GEN6_RC_CTL_RC6p_ENABLE : 0);
> > >
> > > Or did I get the operator precedence wrong?
> >
> > You're right, no cookie for Eugeni. :)  This would have prevented RC6
> > from ever getting enabled though, which should have the same effect as
> > the patch intended, though at the cost of higher power consumption.
> >
> 
> Actually, no, it got RC6p enabled - so it got to have all the power savings
> of RC6 plus some additional ones in the range of 0.1W, but it also resulted
> in the very same problem as before, when both RC6 and RC6p were enabled.
> 
> So, from what we've seen with
> https://wiki.ubuntu.com/Kernel/PowerManagementRC6, the graphics corruptions
> do only happen when RC6p is enabled (either together with RC6, or
> individually, on its own). If we have only RC6, all the issues are gone so
> far.
> 
> So this bad patch had its use after all - it served to finally isolate and
> prove that the i915_enable_rc6-related issues are caused directly by RC6p.

Oh you're right; I had the bit positions mixed up...  I thought the
higher level bit toggled all RC6 functionality, but that's kept
separate from this.

-- 
Jesse Barnes, Intel Open Source Technology Center

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