[coreboot] USB problem with Haswell+LynxPointLP motherboards
aladyshev at nicevt.ru
Wed Oct 18 14:58:24 CEST 2017
Ok, I've done some investigations about what can be the source of my problem:
1) last value of COMMAND register from BIOS
I've dumped all EHCI registers (pci and memory) at the beginning of linux kernel EHCI initialization. And to my surprise pretty all memory registers in original BIOS look like almost uninitialized compared to my coreboot+seabios image. I don't really know how to work with EHCI controller, but seabios do it through periodic and async schedule and their enable bits (in COMMAND register from commit!) aren't active in original BIOS. I've tried to disable ehci initialization in seabios and after that registers dump started to look almost the same, compared to original bios, but it didn't solve my issue. Also without them USB doesn't work in grub. So it doesn't seem like BIOS last value of COMMAND register really matter.
There are special registers for EHCI controller SMIs in its pci config space:
-USB EHCI Legacy Support Extended
-Intel Specific USB 2.0 SMI
But in both of them SMIs are disabled as in coreboot+seabios image as in original bios.
In original BIOS ACPI doesn't do anything to EHCI COMMAND register from commit. It doesn't have a name for it or declare it in some region. Anyway I've copied almost all asl EHCI controller code, but it didn't help.
BUT! I've provided MP-table and PIRQ table to coreboot and I can say that the problem disappears when I boot with 'acpi=off' parameter!
Also it disappears when I boot with 'nolapic' parameter
What do they have in common??
From: jwerner at google.com [mailto:jwerner at google.com] On Behalf Of Julius Werner
Sent: Tuesday, October 10, 2017 5:56 AM
To: Аладышев Константин
Subject: Re: [coreboot] USB problem with Haswell+LynxPointLP motherboards
> 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 afterwards.
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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