I noticed a #nixos test occasionally failing, and ended up tracing it down to a bug in the qemu USB EHCI code 🤓
Follow along at: https://github.com/NixOS/nixpkgs/issues/170803
Learned a lot about qemu and EHCI.
Fix now submitted upstream: https://lists.nongnu.org/archive/html/qemu-devel/2022-05/msg01484.html
@Pol Thanks! TBH I was ready to give up on several occasions ;) - the reproducer from Lin Ma and being able to exchange ideas with Naïm on the issue tracker was very useful and motivating.
And yeah very satisfying to see all those messy printf experiments eventually culminating in a small and IMHO pretty convincing fix ;)