[Intel-gfx] [PATCH 1/2] drm/i915: skip the first 4k of stolen memory on everything >= gen8

[Paulo Zanoni]

Em Ter, 2016-12-13 às 18:01 -0200, Paulo Zanoni escreveu:
> Em Ter, 2016-12-13 às 17:57 -0200, Paulo Zanoni escreveu:
> > 
> > BSpec got updated and this workaround is now listed as standard
> > required programming for all subsequent projects.
> > 

Ok, so I got confirmation from the bug reporter that this patch is the
patch that actually fixes his screen flickering bugs. I suppose we're
initializing some ring on the first page and that's what really messes
up things (last time I checked, we did initialize a ring there on my
machine).

The corruption caused by random bugs flipping in the very first pixel
line of the frontbuffer is probably not very noticeable, so we probably
won't get bug reports for patch 2 specifically.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94605
Tested-by: Dominik Klementowski <dominik232 at gmail.com>

> 
> Cc: stable at vger.kernel.org
> > 
> > Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_gem_stolen.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c
> > b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > index efc0e74..b1c8897 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > @@ -55,10 +55,9 @@ int i915_gem_stolen_insert_node_in_range(struct
> > drm_i915_private *dev_priv,
> >  		return -ENODEV;
> >  
> >  	/* See the comment at the drm_mm_init() call for more
> > about
> > this check.
> > -	 * WaSkipStolenMemoryFirstPage:bdw,chv,kbl (incomplete)
> > +	 * WaSkipStolenMemoryFirstPage:bdw+ (incomplete)
> >  	 */
> > -	if (start < 4096 && (IS_GEN8(dev_priv) ||
> > -			     IS_KBL_REVID(dev_priv, 0,
> > KBL_REVID_A0)))
> > +	if (start < 4096 && INTEL_GEN(dev_priv) >= 8)
> >  		start = 4096;
> >  
> >  	mutex_lock(&dev_priv->mm.stolen_lock);
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