On Wed, 2018-01-31 at 21:22 -0800, Rodrigo Vivi wrote:
> 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.nik...@intel.com>
> > > Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
> > > Signed-off-by: Rodrigo Vivi <rodrigo.v...@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*
>
I have very little idea of how reliable VBT's are on SDP's or if they
are always updated with the correct values. Having those fall back
checks based on SKU and ports, which we know are definite HW limits, I
feel is safer. However, I'll leave this to you as my knowledge is fairly
limited.
> 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) ?
Yes.
>
> >
> > -DK
> >
> >
> > > +
> > > + if (IS_CANNONLAKE(dev_priv))
> > > + return cnl_adjusted_max_rate(intel_dp);
> > > +
> > > + return INT_MAX; /* No adjusted limit */
> > > }
> > >
> >
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