HP actually has a working firmware update mechanism for all their gear. Its a bootable Linux liveDVD that starts into a browser talking to a local Tomcat instance which applies necessary patches. For many cases its also possible to invoke patching from your normal Linux installation. However, a reboot is mostly still necessary, e.g. for disk firmware which the controller applies after its own new firmware has been loaded (sometimes takes more than one reboot).

The system is quite a lot older than fwupd and less flakey usually. Google for hpsum or HP SPP