RISC-V International
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The Linux kernel has been merged mainline in the 4.15 merge window in November 2017.
Since then a range of Distributions have RISC-V ports. E.g.:
RISC-V Status
The Linux kernel supports RV64G as well as RV32G.
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Work is in progress adding the port, with the first commit made on 23rd April 2021.