drm/i915/dp: Reset intel_dp->link_trained before retraining the link

commit d13e2a6e95 upstream.

Regularly retraining a link during an atomic commit happens with the
given pipe/link already disabled and hence intel_dp->link_trained being
false. Ensure this also for retraining a DP SST link via direct calls to
the link training functions (vs. an actual commit as for DP MST). So far
nothing depended on this, however the next patch will depend on
link_trained==false for changing the LTTPR mode to non-transparent.

Cc: <stable@vger.kernel.org> # v5.15+
Cc: 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/20240708190029.271247-2-imre.deak@intel.com
(cherry picked from commit a4d5ce6176)
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -3627,6 +3627,8 @@ int intel_dp_retrain_link(struct intel_encoder *encoder,
 		    !intel_dp_mst_is_master_trans(crtc_state))
 			continue;
 
+		intel_dp->link_trained = false;
+
 		intel_dp_check_frl_training(intel_dp);
 		intel_dp_pcon_dsc_configure(intel_dp, crtc_state);
 		intel_dp_start_link_train(intel_dp, crtc_state);