Avi Kivity wrote:
Blue Swirl wrote:
I don't understand. It's not a device that needs bouncing, it's a
particular transfer. This could be either due to the transfer
targeting
mmio, or due to the transfer requiring a transformation.
Should the bouncing be something more much complex, for example
negotiated between the devices? Or maybe the devices set up a
transforming and non-transforming channel (which the other end should
be able to transform some more) and use them as needed?
Yes. We already have two cases:
- may do partial request: useful for block storage where requests can
be huge
- need full request: networking, where you can't send or receive half
a packet; on the other hand, packets are small (even with tso)
You're adding a third case, always bounce, when the data undergoes a
transformation which can't happen in-place.
IMHO, IOMMU translation is distinct from mapping/data transformation. I
would think the IOMMU translation API would be different in that it took
a physical address and returned a physical address.
The IOMMU DMA API (which could transform data potentially) should return
a virtual address and data a physical address. In the normal case
(non-transforming IOMMU), it should just fall-through to CPU DMA API
(which is just map/unmap).
The PCI DMA API would normally fall through to the IOMMU DMA API.
So we would have:
PCI DMA map(addr):
if IOMMU:
return IOMMU DMA map(addr)
return CPU DMA map(addr)
IOMMU DMA map(addr):
new_address = IOMMU translate(addr)
if transform:
return IOMMU byte-swap map(addr)
return CPU DMA map(addr)
Regards,
Anthony Liguori
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