Messages in this thread | | | From | "Tian, Kevin" <> | Subject | RE: [PATCH 2/4] iommu: Add PASID support for DMA mapping API users | Date | Thu, 9 Dec 2021 01:56:37 +0000 |
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> From: Jacob Pan <jacob.jun.pan@linux.intel.com> > Sent: Thursday, December 9, 2021 2:50 AM > > > Can a device issue DMA requests with PASID even there's no system > IOMMU > > or the system IOMMU is disabled? > > > Good point. > If IOMMU is not enabled, device cannot issue DMA requests with PASID. This > API will not be available. Forgot to add dummy functions to the header. >
PASID is a PCI thing, not defined by IOMMU.
I think the key is physically if IOMMU is disabled, how will root complex handle a PCI memory request including a PASID TLP prefix? Does it block such request due to no IOMMU to consume PASID or simply ignore PASID and continue routing the request to the memory controller?
If block, then having an iommu interface makes sense.
If ignore, possibly a DMA API call makes more sense instead, implying that this extension can be used even when iommu is disabled.
I think that is what Baolu wants to point out.
Thanks Kevin
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