I'm not sure exactly when the first 840 EVO firmware which advertised queued trim support (along with SATA 3.1/3.2 support) was released, but I think that if you last updated firmware (or acquired the drive) before October 2014, you're safe.

However, if you don't update your firmware, you'll suffer from significant performance degradation when reading old files: http://www.anandtech.com/show/9196/samsung-releases-second-8...