Bug#1050352: backside USB-ports stop working after some time

[Bjørn Mork <bjorn@mork.no>]

I'm no expert, but I believe this is a firmware problem you just have to
find some acceptable workaround for.  It's not a kernel bug.

The differences you have found by comparing kernels and building you own
all boil down to the fact that Debian enables DMAR devices by
default. That's not a regression, or a bug at all.  It's just a
different default which happens to expose latent bugs in drivers and/or
device firmware.  You should be able to boot the Debian kernels with
"intel_iommu=off", achieving exactly the same result as all those other
working kernels.

See https://bugzilla.kernel.org/show_bug.cgi?id=215906 for further
details on the specific Via firmware bug.  Mathias Nyman (who is the
xhci driver maintainer) suggests that a workaround might be possible in
the driver, provided that the exact details of the bug can be
identified. Maybe you can work with him to help find a driver
workaround?

Otherwise the best option is probably to disable DMAR on this system,
like you've already figured out.  Either i BIOS settings, or simply by
booting with "intel_iommu=off".

Just my .02 € as another end user with buggy firmwares all around me.



Bjørn