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

[Matt Roper <matthew.d.roper@intel.com>]

On Wed, Apr 06, 2016 at 01:28:25PM +0300, Ville Syrjälä wrote:
> 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.

Oh strange; the note about being unused for BXT gets hidden if you're
filtering the bspec on BXT.  I have to remove the filter to see it.
Seems a bit backwards...

Thanks for the confirmation and background.


Matt

> 
> > 
> > 
> > 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

-- 
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795
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