Re: [PATCH] drm/i915/bdw: Only use 2g GGTT for 32b platforms

[Ben Widawsky <ben@bwidawsk.net>]

On Wed, May 07, 2014 at 09:42:57AM +0200, Daniel Vetter wrote:
> On Tue, May 06, 2014 at 09:58:59PM -0700, Ben Widawsky wrote:
> > From: Ben Widawsky <benjamin.widawsky@linux.intel.com>
> > 
> > Daniel requested in the bug that I use a 3GB fallback size. Since this
> > is not in the spec as a valid size, I decided against it. We could
> > potentially add a patch to bump it to 3GB on top of this one.
> > 
> > This probably should be CC: stable - but I'll let the powers that be
> > decide that one.
> > 
> > v2: Change ifdef to 32b, instead of ifndef
> > update comment
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76619
> > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> > ---
> >  drivers/gpu/drm/i915/i915_gem_gtt.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> > index 846b6ee..d03a540 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> > @@ -1759,6 +1759,14 @@ static inline unsigned int gen8_get_total_gtt_size(u16 bdw_gmch_ctl)
> >  	bdw_gmch_ctl &= BDW_GMCH_GGMS_MASK;
> >  	if (bdw_gmch_ctl)
> >  		bdw_gmch_ctl = 1 << bdw_gmch_ctl;
> > +
> > +#ifdef CONFIG_32BIT
> > +	/* Limit 32B platforms to a 2GB GGTT
> > +	4 << 20 / pte size * PAGE_SIZE */
> > +	if (bdw_gmch_ctl > 4)
> > +		bdw_gmch_ctl = 4;
> 
> Comment needs CodingStyle polish and we might as well return the right
> value directly instead of adjusting bdw_gmch_ctl. With that polish applied
> this is Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>o
> 
> And yes most definitely Cc: stable@vger.kernel.org since it's a
> regression.
> 
> Aside: Please add the regression tags when handling bugs, I need those for
> tracking and stats.
> -Daniel
> 

I don't know what a regression tag is.

> > +#endif
> > +
> >  	return bdw_gmch_ctl << 20;
> >  }
> >  
> > -- 
> > 1.9.2
> > 
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> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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-- 
Ben Widawsky, Intel Open Source Technology Center