Recently I did an in-place upgrade, from SQL 2012 SP1 to 2014 SP2, this for upgrading ConfigMgr 2012 R2 SP1 to Current Branch (1511) afterwards. Nothing wrong here you may think.
During upgrade the reporting part failed with the following error: "A Secure Sockets Layer (SSL) certificate is not configured on the Web site." Trick is, within Reporting Services Configuration Manager, there may be IP-addresses reserved for both http and https, where the one for https must be connected to an SSL certificate.
After starting upgrade again (with the command: setup.exe /action=repair /instancename=<instance>), there was another error: "The Report Server WMI provider cannot create the virtual directory." This occurs when you call SetVirtualDirectory and the UrlString is already reserved. To continue, clear all URL reservations by calling RemoveURL and then try again."
That's another nasty issue if you ask me! I did several installations, with several configurations but it didn't work out for me. With the command: "netsh http show urlacl" all registered URL's can be seen. With the command: "netsh http delete urlacl URL=<url>:<port>" they can be deleted too. When lucky removing the Reportserver URL's is enough, but it didn't work out for me.
Therefore I removed Reporting Services, and installed it again. After installation you may see this message too: "The report server installation is not initialized." To solve this you need to restore the encryption key created earlier, or delete encrypted content. This can be done in Reporting Services Configuration Manager as well.
After 3 error messages, Reporting is running fine on SQL Server 2014 SP2. Now it's time to start the ConfigMgr upgrade finally :-)