[Intel-gfx] [PATCH] drm/i915/fbc: Assume maximum 8mb of stolen is used for gen8+

[Vivi, Rodrigo]

On Wed, 2016-10-26 at 22:45 +0200, David Weinehall wrote:
> On Wed, Oct 26, 2016 at 11:22:00AM -0700, Rodrigo Vivi wrote:
> > Since Broxton has same FBC block as BDW+ let's assume it also
> > don't have access to the stolen usable range.
> > 
> > FBC is currently not saving power on Broxton and I believe
> > the compression threshold is limited to 1x.
> > 
> > Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > Cc: Marc Herbert <marc.herbert at intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_fbc.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
> > index cbe2ebd..640db67 100644
> > --- a/drivers/gpu/drm/i915/intel_fbc.c
> > +++ b/drivers/gpu/drm/i915/intel_fbc.c
> > @@ -530,12 +530,11 @@ static int find_compression_threshold(struct drm_i915_private *dev_priv,
> >  	int ret;
> >  	u64 end;
> >  
> > -	/* The FBC hardware for BDW/SKL doesn't have access to the stolen
> > +	/* The FBC hardware for gen8+ doesn't have access to the stolen
> >  	 * reserved range size, so it always assumes the maximum (8mb) is used.
> 
> Might I suggest correcting the comment to say megabyte instead of
> millibit while at it?

you mean s/8mb/8MB right? I can change it in a v3 for sure.

> 
> >  	 * If we enable FBC using a CFB on that memory range we'll get FIFO
> >  	 * underruns, even if that range is not reserved by the BIOS. */
> > -	if (IS_BROADWELL(dev_priv) ||
> > -	    IS_SKYLAKE(dev_priv) || IS_KABYLAKE(dev_priv))
> > +	if (INTEL_INFO(dev_priv)->gen <= 8)
> 
> INTEL_GEN(dev_priv)

yeap, good point. will change that later .

Although for Marc the old style has more chance to get applied on his
tree for now.

Let's wait for his confirmation before the v3 anyway.

> 
> Also, shouldn't this be >= 8? Also, 

duh! sorry!
Marc already pointed me this mistake... v2 was sent already.

> remember that gen8 also includes
> CherryView -- is the behaviour the same there?

chv doesn't have fbc so I hope it never reaches this path...

> 
> >  		end = ggtt->stolen_size - 8 * 1024 * 1024;
> >  	else
> >  		end = ggtt->stolen_usable_size;
> > -- 
> > 1.9.1
> > 
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