Xiaomi has a terrible history with releasing kernel sources—a direct violation of the General Public License. The company looks to have seen the light, with a company spokesperson declaring that devices will now have their sources released to the public, albeit with a slight caveat.
https://www.notebookcheck.net/Xiaomi-promises-to-release-kernel-sources-for-its-devices-but-there-s-a-catch.297860.0.html