Re: [PATCH] drm/i915/dp: Add current maximum eDP link rate to sink_rate array.

[Mario Kleiner <mario.kleiner.de@gmail.com>]

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On Thu, Jan 9, 2020 at 4:27 PM Ville Syrjälä <ville.syrjala@linux.intel.com>
wrote:

> On Thu, Jan 09, 2020 at 04:07:52PM +0100, Mario Kleiner wrote:
> > If the current eDP link rate, as read from hw, provides a
> > higher bandwidth than the standard link rates, then add the
> > current link rate to the link_rates array for consideration
> > in future mode-sets.
> >
> > These initial current eDP link settings have been set up by
> > firmware during boot, so they should work on the eDP panel.
> > Therefore use them if the firmware thinks they are good and
> > they provide higher link bandwidth, e.g., to enable higher
> > resolutions / color depths.
> >
> > This fixes a problem found on the MacBookPro 2017 Retina panel:
> >
> > The panel reports 10 bpc color depth in its EDID, and the UEFI
> > firmware chooses link settings at boot which support enough
> > bandwidth for 10 bpc (324000 kbit/sec to be precise), but the
> > DP_MAX_LINK_RATE dpcd register only reports 2.7 Gbps as possible,
> > so intel_dp_set_sink_rates() would cap at that. This restricts
> > achievable color depth to 8 bpc, not providing the full color
> > depth of the panel. With this commit, we can use firmware setting
> > and get the full 10 bpc advertised by the Retina panel.
> >
> > Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 23 +++++++++++++++++++++++
> >  1 file changed, 23 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 2f31d226c6eb..aa3e0b5108c6 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -4368,6 +4368,8 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
> >  {
> >       struct drm_i915_private *dev_priv =
> >               to_i915(dp_to_dig_port(intel_dp)->base.base.dev);
> > +     int max_rate;
> > +     u8 link_bw;
> >
> >       /* this function is meant to be called only once */
> >       WARN_ON(intel_dp->dpcd[DP_DPCD_REV] != 0);
> > @@ -4433,6 +4435,27 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
> >       else
> >               intel_dp_set_sink_rates(intel_dp);
> >
> > +     /*
> > +      * If the firmware programmed a rate higher than the standard sink
> rates
> > +      * during boot, then add that rate as a valid sink rate, as fw
> knows
> > +      * this is a good rate and we get extra bandwidth.
> > +      *
> > +      * Helps, e.g., on the Apple MacBookPro 2017 Retina panel, which
> is only
> > +      * eDP 1.1, but supports the unusual rate of 324000 kHz at bootup,
> for
> > +      * 10 bpc / 30 bit color depth.
> > +      */
> > +     if (!intel_dp->use_rate_select &&
> > +         (drm_dp_dpcd_read(&intel_dp->aux, DP_LINK_BW_SET, &link_bw, 1)
> == 1) &&
> > +         (link_bw > 0) && (intel_dp->num_sink_rates <
> DP_MAX_SUPPORTED_RATES)) {
> > +             max_rate = drm_dp_bw_code_to_link_rate(link_bw);
> > +             if (max_rate >
> intel_dp->sink_rates[intel_dp->num_sink_rates - 1]) {
> > +                     intel_dp->sink_rates[intel_dp->num_sink_rates] =
> max_rate;
> > +                     intel_dp->num_sink_rates++;
> > +                     DRM_DEBUG_KMS("Adding max bandwidth eDP rate %d
> kHz.\n",
> > +                                   max_rate);
> > +             }
>
> Hmm. I guess we could do this. But plese put it into a separate
> function so we don't end up with that super ugly if condition.
>
>
Ok. Does static void intel_edp_add_bootup_rate() good to you? Or
intel_edp_add_fw_rate()?

The debug message should probably be a bit more explicit. Eg.
> something like:
> "Firmware using non-standard link rate %d kHz. Including it in sink
> rates.\n"
>

Ok.


> I'm also wondering if we shouldn't just add the link rate to the sink
> rates regradless of whether it's the highest rate or not...
>
>
I tried to be conservative, and simple, but yes, one could add it anyway.
Would need to preserve the order in the sink_rates[] array.
Your choice, your're the expert :)


> > +     }
> > +
> >       intel_dp_set_common_rates(intel_dp);
> >
> >       /* Read the eDP DSC DPCD registers */
> > --
> > 2.24.0
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Ville Syrjälä
> Intel
>

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