[coreboot] USB problem with Haswell+LynxPointLP motherboards

Julius Werner jwerner at chromium.org
Tue Oct 10 04:55:34 CEST 2017

> And now I'm kinda stuck. The effect of this commit doesn't seem to interface
> with bios for me. So how does original IBASE/DFI bios can overcome code
> error before this commit?
> What can be the source of my problem? What should I investigate more precise
> based on result that I've got?

My gut feeling would be to blame ACPI. The Linux patch is about
caching a host controller register in the kernel, and in some cases
(e.g. ehci_reset()), the patch re-reads the cached version from the
hardware whereas the previous code didn't. If some BIOS ACPI mucks
with that register, it's possible that this got the kernel's cached
copy out of sync before this patch, but with the patch the kernel will
re-read it from the hardware at the right time. Maybe only coreboot's
ACPI routines touch the register in that path, or maybe the vendor
BIOS' routines were more careful to restore the original state

Besides ACPI this could also be in SMM code, I guess (especially if
the problem occurs around system suspend/resume, although it sounds
like it doesn't for you).

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