On Tue, Oct 13, 2020 at 02:42:38PM +0100, Robin Murphy wrote:
> I still think this situation would be best handled with a variant of
> dma_ops_bypass that also guarantees to bypass SWIOTLB, and can be set
> automatically when attaching to an unmanaged IOMMU domain.
dma_ops_bypass should mostly do the right thing as-is. swiotlb bouncing
is triggered of two things:
1) the dma_mask. This is under control of the driver, and obviously
if it is too small for a legit reason we can't just proceed
2) force_dma_unencrypted() - we'd need to do an opt-out here, either
by a flag or by being smart and looking for an attached iommu on
the device
> That way the
> device driver can make DMA API calls in the appropriate places that do the
> right thing either way, and only needs logic to decide whether to use the
> returned DMA addresses directly or ignore them if it knows they're
> overridden by its own IOMMU mapping.
I'd be happy to review patches for this.
