According to The Information (behind paywall):
RISC-V, which is anchored by a nonprofit foundation, is gaining popularity among companies frustrated by the limitations and high costs of current chip designs such as those offered by Arm. Tesla recently joined the RISC-V Foundation, and also is considering RISC-V, which is free to use, for its new chip efforts, said a person familiar with the matter.
More about the RISC-V open source technology:
More than 80 tech companies including Google, Qualcomm and Samsung have joined together to develop a new open-source chip design that offers a much cheaper way to build chips for new technologies like autonomous vehicles. If the effort succeeds, it could seriously undercut SoftBank-owned Arm Holdings, which has been trying to extend its dominance in smartphone chips into new areas.