Loongson Continues Working On LoongArch For Linux, But It's Mostly Copying MIPS Code
Written by Michael Larabel in Hardware on 25 August 2021 at 05:48 AM EDT. 23 Comments
HARDWARE --
Loongson this summer rolled out their 3A5000 processors built on their own "LoongArch" ISA. While the company continues claiming that LoongArch is "not MIPS", the Linux kernel code they continue proposing for the mainline Linux kernel points to it being a close facsimile to MIPS.

LoongArch is the Chinese company's effort to have a domestic processor not dependent upon foreign technology. While the company has long produced MIPS-based processor designs, with their new processors they are using LoongArch as they describe as "a new RISC ISA" for the Chinese CPU market.

Loongson Technology has been working on bringing up this new LoongArch architecture within the mainline Linux kernel. While their patches keep referring to it as "not MIPS", the code in large part is copying MIPS code already within the kernel.

This is also causing frustrations by upstream maintainers reviewing LoongArch patches and questioning the LoongArch vs. MIPS. In one of the patches, "You keep saying "not MIPS", and yet all I see is a blind copy of the MIPS code...This is still the same antiquated, broken MIPS code, only with a different name."

Some of the LoongArch patches do appear new but so far not pointing to any groundbreaking differences or exciting new capabilities of these processors. Unfortunately the public documentation from Loongson Technology has been lacking as well for showing any ISA differences, etc. We'll see what else comes out when they push out more kernel and toolchain patches for LoongArch.

If nothing is ultimately presented to make the code dramatically different from the existing MIPS64 code and a lot of code duplication, we'll see what Linus Torvalds and others have to say about upstreaming it when the time comes. Already back in 2018 given the success of RISC-V, kernel developers thought China's C-SKY might have been the last new CPU architecture for the Linux kernel.
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