I've played around with Grafana and FactoryTalk Historian SE (Rockwells repackaged OSIsoft PI) for testing myself, and I've also been using someone elses install of Grafana talking to OSIsoft PI.
Grafana has the OSIsoft-PI data source plugin. (Search for osisoft in the Grafana Configuration\Plugin area)
That will need PI-WebAPI installed and configured to access the historian.
(Install kit is in the Redist\Advanced Server Options\PiWebAPI folder on the historian disk on 7/8)
When I played with it myself, it was a quick and dirty install, PI-WebAPI on an alternate port to avoid conflicts and I just used basic authentication.
Seemed to work pretty well on my test install, but I didn't read enough to make it production grade/secure, I only have end user access to a proper install.