[Bug 215906] DMAR fault when connected usb hub (xhci_hcd)

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=215906

--- Comment #21 from Rolf Reintjes (lists.rolf@reintjes.nrw) ---
(In reply to Michał Pecio from comment #20)
> By a complete accident I found that VL805 has a known bug where it
> overfetches transfer rings:
> https://github.com/raspberrypi/linux/issues/4685
> 
> Rolf, there is a workaround for similar bug in Zhaoxin hardware which may
> solve your IOMMU faults.
> 
> Update to at least v6.6, or the latest v6.12 series if it's not a problem.
> 
> Run the following (if using a USB keyboard put it all in a script):
> rmmod xhci_pci
> rmmod xhci_hcd
> modprobe xhci_hcd quirks=0x200000000000
> modprobe xhci_pci
> 
> Verify that it worked:
> dmesg |grep quirks
> [122123.422469] xhci_hcd 0000:08:00.0: hcc params 0x002841eb hci version
> 0x100 quirks 0x0000200000000890
>                                                                             
> ^-- here
> And see if it helps.

Thank you very much.

I just tried it and it works. The USB port runs fine.

But what is actually done here?
modprobe xhci_hcd quirks=0x200000000000
A setting is given to the driver when starting, but what does this setting
mean?

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