drm/i915/dp: Keep cached LTTPR mode up-to-date

Nothing depends on the cached LTTPR mode, however for consistency keep
it up-to-date with the value programmed to the DPCD register.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240708190029.271247-5-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_dp_link_training.c

@@ -114,7 +114,13 @@ intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable)
 	u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT :
 			  DP_PHY_REPEATER_MODE_NON_TRANSPARENT;
 
-	return drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) == 1;
+	if (drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) != 1)
+		return false;
+
+	intel_dp->lttpr_common_caps[DP_PHY_REPEATER_MODE -
+				    DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV] = val;
+
+	return true;
 }
 
 static bool intel_dp_lttpr_transparent_mode_enabled(struct intel_dp *intel_dp)