Re: Lowspeed USB device enumerationg under 5.4.288, but not under 6.8.1

[Michal Pecio <michal.pecio@gmail.com>]

On Wed, 6 May 2026 07:19:53 +0000, Fischer, Simon wrote:
> I have been able to reproduce the problem with a current (6.19)
> kernel and independent of PREEMPT_RT status. But I have also been
> able to identify that the difference between my Ubuntu provided 5.4
> and 6.8 kernels that leads to the problem, is actually the CONFIG_HZ
> build config parameter.
> 
> Ubuntu's 6.8 kernel is by default built with CONFIG_HZ=1000, while
> the old 5.4 kernel was built with CONFIG_HZ=250. If I rebuild
> Ubuntu's 5.4 with 1000Hz, I also cannot talk to the devices, and when
> I compile 6.19 or 6.8 with 250Hz, they work (currently running a
> rebuilt Ubuntu 6.8.1 with only that one parameter updated, I
> sometimes still see errors, but an automatic retry of the driver is
> then successful).

Quite fascinating ;)

BTW, I would still be interested to see 'lsusb -v' of any low-speed
isochronous device. Can such a thing seriously work with xhci?

> So, a regression this is not :-)
>
> Since I cannot imagine in what way the system interrupt frequency
> would directly affect this part in such a reproducible and
> significant manner, I would think it more likely that the USB core or
> xhci drivers actually use that setting value somewhere themselves and
> maybe wrongly. So this should probably realy go to some other list.
> If you know which, I would greatly appreciate you forwarding my
> information  or telling me where to take it.

Per Documentation/admin-guide/reporting-issues.rst, try your best guess
which kernel part might be responsible and report there.

In short: linux-usb@vger.kernel.org

Regards,
Michal