Mitchell gave a presentation on the status of the FreeBSD/riscv64 platform at the June developers' summit, part of BSDCan 2024. The presentation discussed the challenges of supporting the evolving RISC-V ISA, and gave a brief overview of some available hardware targets. It is informal in nature, but available to watch on youtube.

https://www.youtube.com/watch?v=O7zW7Z9U0ns

Work has been ongoing to support the JH7110 RISC-V SoC in FreeBSD. This SoC is present in several existing RISC-V SBCs. The primary support target is the VisionFive v2, but this work is likely to benefit similar hardware such as the Pine64 Star64 and the Milk-V Mars.

At present, the support in CURRENT is partially complete. What is working: * UART * clk/reset drivers * MMC/SD

The next target is working ethernet, which is supported with extensions to the if_eqos driver. This code is functional, but still in review.

Work on this has been performed by Jari, with review, testing, and integration from Mitchell.

https://wiki.freebsd.org/riscv/StarFive

As discussed in the devsummit presentation, these CPUs present several barriers to support. The problems come primarily from custom vendor extensions: non-coherent device I/O with custom cache management instructions, and a custom (spec-violating) implementation of page-based memory types. Combined, these quirks require difficult and invasive changes to pmap, busdma, and early boot code.

At the same time, we are seeing an increasing amount of available hardware based on this IP, and so support becomes a repeated question and incentive.

Work on page-based memory types is underway and expected to land soon in CURRENT. This feature allows individual virtual memory pages to be assigned specific properties, e.g. cacheability requirements. The riscv64 pmap has been extended to support the official RISC-V 'Svpbmt' extension, and the T-HEAD version of PBMT. These alternative encodings are incompatible, but provide similar functionality.

Work on the device coherence and cache management challenges will begin next quarter.

The hope is that this foundational work will (eventually) enable board support for available RISC-V hardware such as: * Allwinner D1 (Nehza) * Sipeed Lichee Pi 4A * Beagle-V Ahead * Milk-V Pioneer

Experimental support for the RISC-V hypervisor in bhyve/vmm(4) is under active development. Currently, single-core VMs are possible, and the guest can boot to multi-user.

Note: the "H" (hypervisor) extension is not implemented by any known existing or upcoming RISC-V hardware. It is fully supported by software simulators such as Spike or QEMU.

https://wiki.freebsd.org/riscv/bhyve

Sponsor: The FreeBSD Foundation (mhorne’s work) Sponsor: UKRI (br’s work)