INTR-REMAP error with UDD driver

Jan Kiszka jan.kiszka at
Fri Mar 8 08:14:33 CET 2019

On 08.03.19 02:35, Jeff Webb via Xenomai wrote:
> I have implemented a simple UDD mini-driver (interrupt handler) and an associated Xenomai userspace test program.  This pair of programs works as intended on one machine.  When I tried running the same programs on another machine, I got this error when the first interrupt occurred:
> kernel: [   75.122305] DMAR: DRHD: handling fault status reg 2
> kernel: [   75.123175] DMAR: [INTR-REMAP] Request device [f0:1f.0] fault index ee00 [fault reason 37] Blocked a compatibility format interrupt request

This means the device is under IOMMU interrupt remapping regime, but it was 
programmed to use a standard MSI/MSI-X request, rather than requesting that 
parameters (address/data tuple) from the Linux interrupt management layer that 
will assign a remapping slot and hand out the right values. Now you interrupt is 
stuck in the filter.

Before suggesting the workaround/hack to disable interrupt remapping: How did 
you program MSI/-X? Via proper Linux pci_* helpers?


> I would guess that the [f0:1f.0] in the message is a PCI bus address, but I don't see this via lspci.  The closest match is:
> 00:1f.0 ISA bridge [0601]: Intel Corporation Q67 Express Chipset LPC Controller [8086:1c4e] (rev 05)
> After the first attempt, I see no more of these messages until I reboot, but the UDD driver never receives an interrupt in any case.
> I tried moving my PCI card to five different slots, and finally found one where everything work properly on the second machine.  I can at continue to make progress using the working slot, but I would really like to resolve the issue with the other slots.  Does anyone have any idea what to try next?
> I am using these sources:
> linux-4.14.89.tar
> ipipe-core-4.14.89-x86-2.patch
> xenomai-3.0.8.tar
> I have attached the boot log, config, and cpu information.
> Thanks,
> -Jeff Webb

Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux

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