RISC-V's Linux Kernel Support Is Getting In Better Shape, Maturing On HiFive Unleashed
Written by Michael Larabel in RISC-V on 8 March 2019 at 06:46 AM EST. 3 Comments
RISC-V --
The Linux kernel's RISC-V processor support is getting into good shape now since the support for this open-source processor ISA was originally introduced back for Linux 4.15. Moving forward, it's now expected the support to be maintained and only improve for the HiFive Unleashed developer board.

Since Linux 4.15, the RISC-V support has continued improving with picking up new hardware support and various architectural additions. With the current Linux 5.1 kernel cycle there is now an HWCAP to indicate the CPU capabilities/extensions that the enabled processor(s) support, no longer spinning indefinitely during the boot process, various code clean-ups, and other changes.

The mainline kernel's support for SiFive's HiFive Unleashed board appears to be largely usable now. HiFive Unleashed features the SiFive Freedom U540 SoC, 8GB DDR4, 32MB quad SPI, and micro-SD card. The Freedom U540 SoC features a 4+1 multi-core design clocked at 1.5GHz. While impressive for a first-cut developer board on a new, royalty-free CPU architecture, the price remains lofty for hobbyists/enthusiasts at $999 USD.

Moving forward though with the RISC-V kernel support maturing, RISC-V architecture maintainer Palmer Dabbelt is wanting to ensure the support doesn't regress and as such will begin instituting that all kernel changes are tested on this board as opposed to just the RISC-V emulator.

Palmer commented in the 5.1 pull request, "I've used my standard testing flow (QEMU in Fedora), but now that we're starting to get the kernel in better shape I think it's time to impose some more testing here -- specifically I'm going to require that patches boot on the HiFive Unleashed because we're getting to the point where we can actually expect that to work. I haven't done that for this tag, but I'm going to do it for future ones."

With time we'll hopefully be seeing more affordable RISC-V developer boards come to market and ideally by that time the kernel support will also be in suitable shape for easier/reliable usage.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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