> -----Original Message----- > From: Kandpal, Suraj <suraj.kandpal@xxxxxxxxx> > Sent: Tuesday, June 20, 2023 4:35 PM > To: Murthy, Arun R <arun.r.murthy@xxxxxxxxx>; intel- > gfx@xxxxxxxxxxxxxxxxxxxxx > Subject: RE: [PATCH] drm/i915/display/dp: Add fallback on LT > failure for DP2.0 > > > For DP2.0 as per the Spec on LT failure we need to reduce the lane > > count if the lane count is not equal to 1. If lane count is 1 then > > need to retry with reducing the link rate. > > Maybe adding the section where one can refer this in DP 2.0 spec can help. > Ok Sure! > > > > Signed-off-by: Arun R Murthy <arun.r.murthy@xxxxxxxxx> > > --- > > drivers/gpu/drm/i915/display/intel_dp.c | 20 ++++++++++++++++++-- > > 1 file changed, 18 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c > > b/drivers/gpu/drm/i915/display/intel_dp.c > > index 54ddc953e5bc..2b12ca45596d 100644 > > --- a/drivers/gpu/drm/i915/display/intel_dp.c > > +++ b/drivers/gpu/drm/i915/display/intel_dp.c > > @@ -657,8 +657,20 @@ int > > intel_dp_get_link_train_fallback_values(struct > > intel_dp *intel_dp, > > "Retrying Link training for eDP with same > parameters\n"); > > return 0; > > } > > - intel_dp->max_link_rate = intel_dp_common_rate(intel_dp, > > index - 1); > > - intel_dp->max_link_lane_count = lane_count; > > NIT: Can we add a small comment here on what is being done. > Comments are added below as to what each if condition is doing or is it something different that you are referring to? > > + if (intel_dp->dpcd[DP_MAIN_LINK_CHANNEL_CODING] & > > DP_CAP_ANSI_128B132B) { > > + if (lane_count > 1) { > > + /* Reduce the lane count */ > > + intel_dp->max_link_lane_count = lane_count > > >> 1; > > + intel_dp->max_link_rate = > > intel_dp_common_rate(intel_dp, index); > > + } else { > > + /* Reduce the link rate */ > > + intel_dp->max_link_rate = > > intel_dp_common_rate(intel_dp, index - 1); > > + intel_dp->max_link_lane_count = > > intel_dp_max_common_lane_count(intel_dp); > > + } > > + } else { > > + intel_dp->max_link_rate = > > intel_dp_common_rate(intel_dp, index - 1); > > + intel_dp->max_link_lane_count = lane_count; > > + } > > Also I see a little issue here so previously what used to happen was we > reduced the Link rate first and once we were at the lowest only then proceed > to reduce the lane count so has this been reversed in DP2.0 spec. > Yes here we reduce the lane count until 1 and then reduce the link rate. Ref: Table 3-31 of DP2.1 Spec Thanks and Regards, Arun R Murthy -------------------- > Regards, > Suraj Kandpal > > > } else if (lane_count > 1) { > > if (intel_dp_is_edp(intel_dp) && > > !intel_dp_can_link_train_fallback_for_edp(intel_dp, > > @@ -675,6 +687,10 @@ int > > intel_dp_get_link_train_fallback_values(struct > > intel_dp *intel_dp, > > return -1; > > } > > > > + drm_dbg_kms(&i915->drm, > > + "Retrying Link training with link rate %d and lane count > > %d\n", > > + intel_dp->max_link_rate, intel_dp->max_link_lane_count); > > + > > return 0; > > } > > > > -- > > 2.25.1