drm/radeon: Don't turn off DP sink when disconnected

Turning off the sink in this case causes various issues, because
userspace expects it to stay on until it turns it off explicitly.

Instead, turn the sink off and back on when a display is connected
again. This dance seems necessary for link training to work correctly.

Bugzilla: https://bugs.freedesktop.org/105308
Cc: stable@vger.kernel.org
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_connectors.c

@@ -90,25 +90,18 @@ void radeon_connector_hotplug(struct drm_connector *connector)
 		/* don't do anything if sink is not display port, i.e.,
 		 * passive dp->(dvi|hdmi) adaptor
 		 */
-		if (dig_connector->dp_sink_type == CONNECTOR_OBJECT_ID_DISPLAYPORT) {
-			int saved_dpms = connector->dpms;
-			/* Only turn off the display if it's physically disconnected */
-			if (!radeon_hpd_sense(rdev, radeon_connector->hpd.hpd)) {
-				drm_helper_connector_dpms(connector, DRM_MODE_DPMS_OFF);
-			} else if (radeon_dp_needs_link_train(radeon_connector)) {
-				/* Don't try to start link training before we
-				 * have the dpcd */
-				if (!radeon_dp_getdpcd(radeon_connector))
-					return;
-
-				/* set it to OFF so that drm_helper_connector_dpms()
-				 * won't return immediately since the current state
-				 * is ON at this point.
-				 */
-				connector->dpms = DRM_MODE_DPMS_OFF;
-				drm_helper_connector_dpms(connector, DRM_MODE_DPMS_ON);
-			}
-			connector->dpms = saved_dpms;
+		if (dig_connector->dp_sink_type == CONNECTOR_OBJECT_ID_DISPLAYPORT &&
+		    radeon_hpd_sense(rdev, radeon_connector->hpd.hpd) &&
+		    radeon_dp_needs_link_train(radeon_connector)) {
+			/* Don't start link training before we have the DPCD */
+			if (!radeon_dp_getdpcd(radeon_connector))
+				return;
+
+			/* Turn the connector off and back on immediately, which
+			 * will trigger link training
+			 */
+			drm_helper_connector_dpms(connector, DRM_MODE_DPMS_OFF);
+			drm_helper_connector_dpms(connector, DRM_MODE_DPMS_ON);
 		}
 	}
 }