Re: [Intel-gfx] [PATCH 2/2] drm/i915/dp: Fix LTTPR vswing/pre-emp setting in non-transparent mode

[Imre Deak <imre.deak@intel.com>]

On Tue, Jan 12, 2021 at 08:10:40PM +0200, Ville Syrjälä wrote:
> On Tue, Dec 29, 2020 at 07:22:01PM +0200, Imre Deak wrote:
> > The DP PHY vswing/pre-emphasis level programming the driver does is
> > related to the DPTX -> first LTTPR link segment only. Accordingly it
> > should be only programmed when link training the first LTTPR and kept
> > as-is when training subsequent LTTPRs and the DPRX. For these latter
> > PHYs the vs/pe levels will be set in response to writing the
> > DP_TRAINING_LANEx_SET_PHY_REPEATERy DPCD registers (by an upstream LTTPR
> > TX PHY snooping this write access of its downstream LTTPR/DPRX RX PHY).
> > The above is also described in DP Standard v2.0 under 3.6.6.1.
> > 
> > While at it simplify and add the LTTPR that is link trained to the debug
> > message in intel_dp_set_signal_levels().
> > 
> > Fixes: b30edfd8d0b4 ("drm/i915: Switch to LTTPR non-transparent mode link training")
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c       |  2 +-
> >  .../drm/i915/display/intel_dp_link_training.c | 19 +++++++++++--------
> >  .../drm/i915/display/intel_dp_link_training.h |  3 ++-
> >  3 files changed, 14 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 88a6033d6867..16c563f1a515 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -6057,7 +6057,7 @@ static void intel_dp_process_phy_request(struct intel_dp *intel_dp,
> >  
> >  	intel_dp_autotest_phy_ddi_disable(intel_dp, crtc_state);
> >  
> > -	intel_dp_set_signal_levels(intel_dp, crtc_state);
> > +	intel_dp_set_signal_levels(intel_dp, crtc_state, DP_PHY_DPRX);
> >  
> >  	intel_dp_phy_pattern_update(intel_dp, crtc_state);
> >  
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > index 7876e781f698..d8c6d7054d11 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > @@ -335,21 +335,24 @@ intel_dp_set_link_train(struct intel_dp *intel_dp,
> >  }
> >  
> >  void intel_dp_set_signal_levels(struct intel_dp *intel_dp,
> > -				const struct intel_crtc_state *crtc_state)
> > +				const struct intel_crtc_state *crtc_state,
> > +				enum drm_dp_phy dp_phy)
> >  {
> >  	struct drm_i915_private *dev_priv = dp_to_i915(intel_dp);
> >  	u8 train_set = intel_dp->train_set[0];
> > +	char phy_name[10];
> >  
> > -	drm_dbg_kms(&dev_priv->drm, "Using vswing level %d%s\n",
> > +	drm_dbg_kms(&dev_priv->drm, "Using vswing level %d%s, pre-emphasis level %d%s, at %s\n",
> >  		    train_set & DP_TRAIN_VOLTAGE_SWING_MASK,
> > -		    train_set & DP_TRAIN_MAX_SWING_REACHED ? " (max)" : "");
> > -	drm_dbg_kms(&dev_priv->drm, "Using pre-emphasis level %d%s\n",
> > +		    train_set & DP_TRAIN_MAX_SWING_REACHED ? " (max)" : "",
> >  		    (train_set & DP_TRAIN_PRE_EMPHASIS_MASK) >>
> >  		    DP_TRAIN_PRE_EMPHASIS_SHIFT,
> >  		    train_set & DP_TRAIN_MAX_PRE_EMPHASIS_REACHED ?
> > -		    " (max)" : "");
> > +		    " (max)" : "",
> > +		    intel_dp_phy_name(dp_phy, phy_name, sizeof(phy_name)));
> >  
> > -	intel_dp->set_signal_levels(intel_dp, crtc_state);
> > +	if (intel_dp_phy_is_downstream_of_source(intel_dp, dp_phy))
> > +		intel_dp->set_signal_levels(intel_dp, crtc_state);
> 
> The function name is a bit misleading now I guess since we're not
> actually setting the signal levels here for the LTTPRs. But since
> the debug print is here I guess we want to still call this. And as
> usual I can't think of a better name for this, so I'm willing
> to accept that slight inconsistency.

Agreed, will try to make that more consistent as a follow up.

Btw, checking again the callers of the above, looks like
intel_dp_process_phy_request() also misses the DPCD write for the vs/pe
settings.

> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> >  }
> >  
> >  static bool
> > @@ -359,7 +362,7 @@ intel_dp_reset_link_train(struct intel_dp *intel_dp,
> >  			  u8 dp_train_pat)
> >  {
> >  	memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
> > -	intel_dp_set_signal_levels(intel_dp, crtc_state);
> > +	intel_dp_set_signal_levels(intel_dp, crtc_state, dp_phy);
> >  	return intel_dp_set_link_train(intel_dp, crtc_state, dp_phy, dp_train_pat);
> >  }
> >  
> > @@ -373,7 +376,7 @@ intel_dp_update_link_train(struct intel_dp *intel_dp,
> >  			    DP_TRAINING_LANE0_SET_PHY_REPEATER(dp_phy);
> >  	int ret;
> >  
> > -	intel_dp_set_signal_levels(intel_dp, crtc_state);
> > +	intel_dp_set_signal_levels(intel_dp, crtc_state, dp_phy);
> >  
> >  	ret = drm_dp_dpcd_write(&intel_dp->aux, reg,
> >  				intel_dp->train_set, crtc_state->lane_count);
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.h b/drivers/gpu/drm/i915/display/intel_dp_link_training.h
> > index c3110c032bc2..6a1f76bd8c75 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.h
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.h
> > @@ -18,7 +18,8 @@ void intel_dp_get_adjust_train(struct intel_dp *intel_dp,
> >  			       enum drm_dp_phy dp_phy,
> >  			       const u8 link_status[DP_LINK_STATUS_SIZE]);
> >  void intel_dp_set_signal_levels(struct intel_dp *intel_dp,
> > -				const struct intel_crtc_state *crtc_state);
> > +				const struct intel_crtc_state *crtc_state,
> > +				enum drm_dp_phy dp_phy);
> >  void intel_dp_start_link_train(struct intel_dp *intel_dp,
> >  			       const struct intel_crtc_state *crtc_state);
> >  void intel_dp_stop_link_train(struct intel_dp *intel_dp,
> > -- 
> > 2.25.1
> 
> -- 
> Ville Syrjälä
> Intel
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