drm/i915/dp: read more receiver capability bits on hotplug

When a hotplug event is received, we need to check the receiver cap bits
in case they've changed (as they might with a hub or chain config).
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -1522,6 +1522,8 @@ intel_dp_link_down(struct intel_dp *intel_dp)
 static void
 intel_dp_check_link_status(struct intel_dp *intel_dp)
 {
+	int ret;
+
 	if (!intel_dp->base.base.crtc)
 		return;
 
@@ -1530,6 +1532,15 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 		return;
 	}
 
+	/* Try to read receiver status if the link appears to be up */
+	ret = intel_dp_aux_native_read(intel_dp,
+				       0x000, intel_dp->dpcd,
+				       sizeof (intel_dp->dpcd));
+	if (ret != sizeof(intel_dp->dpcd)) {
+		intel_dp_link_down(intel_dp);
+		return;
+	}
+
 	if (!intel_channel_eq_ok(intel_dp)) {
 		intel_dp_start_link_train(intel_dp);
 		intel_dp_complete_link_train(intel_dp);