DMAR table missing, Intel IOMMU not available

DMAR table missing, Intel IOMMU not available

[Daniel Drake]

Hi,

We're working with a number of platforms based on Intel Apollo Lake
and there are some clues suggesting that the IR-PCI-MSI irqchip
functionality would be able to get us out of a tricky situation
described at:

ath9k hardware corrupts MSI Message Data, raises wrong interrupt
http://marc.info/?l=linux-pci&m=150238260726797&w=2

However the affected platforms do not have a DMAR table present. And I
read in the
Intel® Virtualization Technology for Directed I/O spec: "The system
BIOS is responsible for detecting the remapping hardware functions in
the platform and for locating the memory-mapped remapping hardware
registers in the host system address space. The BIOS reports the
remapping hardware units in a platform to system software through the
DMA
Remapping Reporting (DMAR) ACPI table".

Unfortunately since the BIOS authors have not done what the spec
asked, this nice hardware functionality is completely unavailable :(

For now we will have to find an alternative approach to solve the
problem (BIOS can't be changed), but I am curious if there are plans
to have Linux automatically probe the IOMMU through some other means,
given that BIOS authors are apparently not providing the DMAR table in
many cases.

Thanks
Daniel
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