Re: [PATCH] drm/i915/bxt: Set max cdclk frequency properly

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Apr 05, 2016 at 02:55:51PM -0700, Matt Roper wrote:
> On Tue, Apr 05, 2016 at 02:37:19PM -0700, Matt Roper wrote:
> > intel_update_max_cdclk() doesn't have a switch case for Broxton, so
> > dev_priv->max_cdclk_freq gets set to whatever clock frequency we're
> > currently running at (e.g., 144 MHz) rather than the true maximum.  This
> > causes our max dotclock to also be set too low and in turn leads mode
> > verification to reject perfectly valid modes while loading EDID firmware
> > blobs.
> > 
> > Cc: Imre Deak <imre.deak@intel.com>
> > Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> > ---
> 
> One thing I should have mentioned is that it's unclear to me whether we
> should be looking at the cdclk limit bits in the DFSM register like we
> do on SKL/KBL.  The bspec seems to indicate that the register in general
> applies to gen9, including BXT, but the actual meaning of the bits
> doesn't match up with the frequencies we have on BXT.

It also says
"This field is unused on BXT.  Any CD clock frequency limitation must be
done in software."

Anyway the DFSM story is apparently a sad one. See the discussion eg. in
https://lists.freedesktop.org/archives/intel-gfx/2016-February/087510.html
would be nice if someone could pick that up and figure out what we really
want/need to do.

> 
> 
> Matt
> 
> >  drivers/gpu/drm/i915/intel_display.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index af74cdb..924d851 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -5261,6 +5261,8 @@ static void intel_update_max_cdclk(struct drm_device *dev)
> >  			dev_priv->max_cdclk_freq = 450000;
> >  		else
> >  			dev_priv->max_cdclk_freq = 337500;
> > +	} else if (IS_BROXTON(dev)) {
> > +		dev_priv->max_cdclk_freq = 624000;
> >  	} else if (IS_BROADWELL(dev))  {
> >  		/*
> >  		 * FIXME with extra cooling we can allow
> > -- 
> > 2.1.4
> > 
> 
> -- 
> Matt Roper
> Graphics Software Engineer
> IoTG Platform Enabling & Development
> Intel Corporation
> (916) 356-2795
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel OTC
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