power cpu isa open sourced, what is gained?

The phrase "open source" is a buzz phrase. I've heard it used to describe the Unity Engine because "I can download the source code... Hurr Dur".

The "open source" camp prioritizes practicality and the free software camp prioritizes freedom. But I argue freedom is (or at least can be) practical and you're only as free as what's installed on your computer. I'm fixing to build a libre system, I just need all the pieces to finish my infinity gauntlet.

That said, having Power ISA be licensed in a way that respects the four freedoms would be very helpful if people are interested enough in avoiding the IME and PSP dumpster fire. If the general public isn't interested, at best, it will be very expensive initially and use economies of scale to drag down the price over time, but the worse case would be nobody making it. SPARC was GPL licensed and nobody bought into it and there's J-Cores, a libre clone of the Hitachi Super-H that was used in Sega Consoles, (32x, Saturn and Dreamcast) but that hasn't picked up any traction.

So it's hard to say.

"what is gained?"

Potentially a lot. Potentially nothing. It's not clear to me what is intended. So far the ISA itself doesn't show a free license:
https://ibm.ent.box.com/s/1hzcwkwf8rbju5h9iyf44wm94amnlcrv

Compared to RISC-V which does have a free license. But perhaps IBM intends to add one? It's not clear to me.

That says "You may use this documentation solely for developing technology products compatible with Power Architecture in support of growing the POWER ecosystem. You may not modify this documentation..." which is clearly non-free. BUT! On the other hand this may be due for a change because it also says "This agreement does not include rights to create a CPU design to run the POWER ISA unless such rights have been granted by IBM under a separate agreement."

And based on their announcement of it going royalty-free, then I'd think a separate license with IBM would no longer be needed. So it's possible that this is just oudated we'll see licensing changes in the future then. So what is gained? Potentially another ISA that is just as free as RISC-V. And yet, also potentially nothing is gained beyond "you don't have to pay royalties to IBM to make a POWER chip." We'll have to wait and see.

MIPS Open is also not free. I checked the license of the ISA at https://www.mipsopen.com/resources/download/ and you can only use it to create MIPS-compatible stuff. People should be free to create stuff that is incompatible as well.