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

[Takashi Iwai]

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.  Though, the BIOS version on that machine is
fairly old, so of course this can be the cause.

But still I feel uneasy that the bug depends on BIOS version, not the
hardware.

In anyway, I'll check other IVB models whether this problem is
present.


thanks,

Takashi

> -Daniel
> 
> 
> >
> >  drivers/gpu/drm/i915/intel_pm.c | 29 ++++++++++++++++++++++++++++-
> >  1 file changed, 28 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> > index 0cbc0e6..944911e 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -4239,9 +4239,36 @@ void intel_gt_init(struct drm_device *dev)
> >         if (IS_VALLEYVIEW(dev)) {
> >                 dev_priv->gt.force_wake_get = vlv_force_wake_get;
> >                 dev_priv->gt.force_wake_put = vlv_force_wake_put;
> > -       } else if (IS_IVYBRIDGE(dev) || IS_HASWELL(dev)) {
> > +       } else if (IS_HASWELL(dev)) {
> >                 dev_priv->gt.force_wake_get = __gen6_gt_force_wake_mt_get;
> >                 dev_priv->gt.force_wake_put = __gen6_gt_force_wake_mt_put;
> > +       } else if (IS_IVYBRIDGE(dev)) {
> > +               /* IVB configs may use multi-threaded forcewake */
> > +               u32 ecobus;
> > +
> > +               /* A small trick here - if the bios hasn't configured
> > +                * MT forcewake, and if the device is in RC6, then
> > +                * force_wake_mt_get will not wake the device and the
> > +                * ECOBUS read will return zero. Which will be
> > +                * (correctly) interpreted by the test below as MT
> > +                * forcewake being disabled.
> > +                */
> > +               mutex_lock(&dev->struct_mutex);
> > +               __gen6_gt_force_wake_mt_get(dev_priv);
> > +               ecobus = I915_READ_NOTRACE(ECOBUS);
> > +               __gen6_gt_force_wake_mt_put(dev_priv);
> > +               mutex_unlock(&dev->struct_mutex);
> > +
> > +               if (ecobus & FORCEWAKE_MT_ENABLE) {
> > +                       DRM_DEBUG_KMS("Using MT version of forcewake\n");
> > +                       dev_priv->gt.force_wake_get =
> > +                               __gen6_gt_force_wake_mt_get;
> > +                       dev_priv->gt.force_wake_put =
> > +                               __gen6_gt_force_wake_mt_put;
> > +               } else {
> > +                       dev_priv->gt.force_wake_get = __gen6_gt_force_wake_get;
> > +                       dev_priv->gt.force_wake_put = __gen6_gt_force_wake_put;
> > +               }
> >         } else if (IS_GEN6(dev)) {
> >                 dev_priv->gt.force_wake_get = __gen6_gt_force_wake_get;
> >                 dev_priv->gt.force_wake_put = __gen6_gt_force_wake_put;
> > --
> > 1.8.0
> >
> 
> 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>