So does it actually let us neutralize the PSP like the me_cleaner tool, or just poke at it?

It looks like a tool to analyze the psp firmware, which is a necessary step in this process.

Necessary only because AMD isn't being cooperative, that is. It'd be as easy as providing a shim so that the machine can boot without enabling the psp.

The PSP is licensed from ARM, meaning AMD owns none of the IP of the PSP. If they were to cooperate in this effort, ARM would likely sue them for breaking their licensing agreement.

Same reason the recently mainlined Mali drivers (another ARM IP block) got no assistance in development from any of the chip vendors. Touching those projects would break their licensing agreements with ARM and risk having to stop producing their chips that integrate Mali (aka most ARM based chips).

This doesn't sound right. The PSP is an ARM core, but the firmware running on it is likely mostly written by AMD. Also, license agreements can be negotiated.

AMD states that the PSP is "ARM TrustZone ... An Industry Standard Approach" right on their website: https://www.amd.com/en/technologies/security

Wrt renegotiating with ARM, there is no leverage for AMD. TrustZone is already baked into their chips for the next 2 to 3 years, and if the negotiations go badly then ARM could block AMD from selling any processors for at least a year.

AMD did hire a security consultant (due to the Change.org petition) that told them TrustZone was vulnerable, but this means they need to implement their own PSP which is something that will take 3 years or more (silicon has a very elongated development cycle).

Had AMD not been on death's doorstep for the years preceding the new Zen architecture, they likely would have built their own PSP. Being financially insolvent and desperate to meet the requirements of their OEM partners forced them to license a pre-built PSP.

All of the really super-secret security and DRM critical stuff is in the vendor's hardware and code.