Re: [PATCH 3/3] drm/i915: don't rewrite the GTT on resume

From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 3/3] drm/i915: don't rewrite the GTT on resume
Date: Mon, 15 Oct 2012 08:49:33 -0700	[thread overview]
Message-ID: <20121015084933.577dd886@jbarnes-t420> (raw)
In-Reply-To: <453bf0$631iug@azsmga001.ch.intel.com>

On Mon, 15 Oct 2012 10:42:03 +0100
Chris Wilson <chris@chris-wilson.co.uk> wrote:

> On Mon, 15 Oct 2012 09:37:00 +0100, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > On Sun, 14 Oct 2012 19:10:38 -0700, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> > > The BIOS shouldn't be touching this memory across suspend/resume, so
> > > just leave it alone.  This saves us ~50ms on resume on my T420.
> > > 
> > > Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> > > ---
> > >  drivers/gpu/drm/i915/i915_drv.c |    7 ++++++-
> > >  1 file changed, 6 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> > > index 824e3c8..95e2b8b 100644
> > > --- a/drivers/gpu/drm/i915/i915_drv.c
> > > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > > @@ -119,6 +119,10 @@ module_param_named(i915_enable_ppgtt, i915_enable_ppgtt, int, 0600);
> > >  MODULE_PARM_DESC(i915_enable_ppgtt,
> > >  		"Enable PPGTT (default: true)");
> > >  
> > > +int i915_needs_gtt_restore __read_mostly = 0;
> > > +module_param_named(gtt_restore, i915_needs_gtt_restore, int, 0600);
> > > +MODULE_PARM_DESC(gtt_restore, "Rewrite GTT on resume (default: false)");
> > 
> > Wrong way around. This code exists purely because KMS resume was broken
> > on a number of machines without reinitialising the GTT, ergo this is a
> > regression.
> 
> Looking into the history, at the time we wrote the GTT reinit, I believe
> we did not have a GFX_FLUSH_CNTL in the resume path. Now we do, so I'd
> be more inclined to believe that we have fixed a bug in the meantime. If
> so, we only need to be extra careful for gen2.

Yeah good point, do we have victims who can check this for us?

Jesse