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

[Chris Wilson <chris@chris-wilson.co.uk>]

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.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre