I believe SiFive's CPUs and chip designs are not open source generally, although they do open source a lot of related things such as software, specifications, tools. I looked at their GitHub and didn't find any CPUs in there, though there are a lot of repos.
Here's an interesting take on what someone thinks "open source" means in this context: gjsman-1000 wrote: Open source refers solely to the software side of things in these groups and types of projects. Thus, all of the drivers and software you need to use the SiFive is open source and thus you can say it is an open source design. However, it is not an "open hardware" design in that the IP used to design the chip is not released.https://news.ycombinator.com/item?id=25762114
I personally don't think of closed chip designs with open software and specifications as open source chips. That would be like saying Intel and AMD x86s are open source. Though to be fair to those companies, their CPU programming models are much more open than their FPGA programming models, which requires proprietary software and secret specifications to program them at all.
