Re: [PATCH] drm/i915/cnl: Respect VBT max dp rate.

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Thu, Feb 01, 2018 at 02:53:20AM +0000, Pandiyan, Dhinakaran wrote:
> 
> 
> 
> On Wed, 2018-01-31 at 13:20 -0800, Rodrigo Vivi wrote:
> > Since commit 'c4fb60b9aba9 ("drm/i915/bios: add DP max link
> > rate to VBT child device struct")' we have the new entry
> > defined for max dp rate that is in use for CNL.
> > 
> > Let's start using it for all VBT 216+ and
> > also organize the cnl adjusted rates in terms of rate
> > and not array size.
> > 
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_drv.h   |  1 +
> >  drivers/gpu/drm/i915/intel_bios.c |  3 +++
> >  drivers/gpu/drm/i915/intel_dp.c   | 37 +++++++++++++++++++++++++++++--------
> >  3 files changed, 33 insertions(+), 8 deletions(-)
> 
> <snip>
> 
> > +static int intel_dp_adjusted_max_rate(struct intel_dp *intel_dp)
> > +{
> > +	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> > +	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
> > +	const struct ddi_vbt_port_info *info =
> > +		&dev_priv->vbt.ddi_port_info[dig_port->base.port];
> > +
> > +	if (info->dp_max_link_rate)
> > +		return info->dp_max_link_rate;
> 
> What if this value is higher than cnl_adjusted_max_rate() ?

Then VBT knows something about that SKU that we don't?! *shrug*

My understanding is that the purpose of that new VBT field is
 to workaround bugs they know for certain combination and limit
 the max rate even more.

bugs like the one I had in a part here:

https://bugs.freedesktop.org/show_bug.cgi?id=103963

in this case flicker was gone by limiting the max rate.

But yeap, maybe vbt is bugged, so are you suggesting min(vbt, bspec) ?

> 
> -DK
> 
> 
> > +
> > +	if (IS_CANNONLAKE(dev_priv))
> > +		return cnl_adjusted_max_rate(intel_dp);
> > +
> > +	return INT_MAX; /* No adjusted limit */
> >  }
> >  
> 
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