Multi-bridged PCIe devices (Was: Re: iommuu/vt-d issues with LSI MegaSAS (PERC5i))

[Gordan Bobic <gordan@bobich.net>]

 I found this:

 http://lists.xen.org/archives/html/xen-devel/2010-06/msg00093.html

 while looking for a solution to a similar problem. I am
 facing a similar issue with LSI (8408E, 3081E-R) and
 Adaptec (31605) SAS cards. Was there ever a proper, more general
 fix or workaround for this issue?

 These SAS cards experience these problems in dom0. When running
 a vanilla kernel on bare metal, they work OK without intel_iommu
 set. As soon as I set intel_iommu, the same thing happens (on
 bare metal, not dom0).

 Clearly there is something badly broken with multiple layers
 of bridges when it comes to IOMMU in my setup (Intel 5520 PCIe
 root hub -> NF200 bridge -> Intel 80333 Bridge -> SAS controller)

 I tried iommu=dom0-passthrough and it doesn't appear to have
 helped.

 I am not seeing similar problems with other PCIe devices that
 are also, in theory doing DMA (e.g. GPUs), but LSI and Adapted
 controllers appear to be affected for some reason.

 Is there anything else I could try/do to make this work?

 Gordan