One of the two processors (the ARM one) in the PinePhone modem runs a proprietary Linux distro, which can be replaced by a free distro. The code on the Hexagon processor can't be replaced yet though I think.
Yeah, and it's the Hexagon mDSP that's the issue. It's basically THE modem. It has its own RTOS and runs the entire RF stack and whispers to all the other RF parts. The cores that run the Linux distro are just... there. For you to run Android on, normally.
PostmarketOS can run on some devices with almost no blobs - but there's no escaping the modem curse.
https://themodemdistro.com/ https://github.com/the-modem-distro/