lib.systems.riscv-multiplatform: linux-kernel config improvements

[NickCao]

Description of changes

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

---

Add a 👍 reaction to pull requests you find important.

[onny]

What does preferBuiltin = true; mean? Why dropping

extraConfig = ''
  SERIAL_OF_PLATFORM y
'';

[NickCao]

What does preferBuiltin = true; mean?

Even if a kconfig option defaults to y, if preferBuiltin is not set and m is available as an option, m would be set.

Why dropping

extraConfig = ''
  SERIAL_OF_PLATFORM y
'';

It's part of the defconfig since 2018.

[onny]

Great, works for me on VisionFive2 board without manually force PINCTRL_STARFIVE_JH7110_SYS = yes;. Kernel is booting fine 👍

[NickCao]

@onny Do you know who else is working on riscv? I'd like to ping more people before merging such a potentially breaking change.

[onny]

Unfortunately not. We should create a platform maintainer group :)

[NickCao]

Unfortunately not. We should create a platform maintainer group :)

There is @NixOS/exotic-platform-maintainers

[0x4A6F]

There is also #riscv:nixos.org which is scoped to RISC-V topic.

[onny]

Are we save merging this or do we need some more tests?

[NickCao]

Are we save merging this or do we need some more tests?

Let's merge this, it should be a net profit for the riscv platform. Except for these really memory constrained devices that can benefit from a smaller kernel, but they should be using a trimmed down kernel config anyway.