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

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

On Thu, Jan 09, 2020 at 05:26:57PM +0200, Ville Syrjälä 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,

Does it actually or do we just ignore the fact that it reports 3.24Gbps?

If it really reports 3.24 then we should be able to just add that to
dp_rates[] in intel_dp_set_sink_rates() and be done with it.

Although we'd likely want to skip 3.24 unless it really is reported
as the max so as to not use that non-standard rate on other displays.
So would require a bit fancier logic for that.

> > 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.
> 
> 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"
> 
> 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...
> 
> > +	}
> > +
> >  	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

-- 
Ville Syrjälä
Intel
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