On 01/02/18 10:18, Jonathan Cameron wrote:
Hi All,
We have a crypto accelerator which needs to have a few different settings
depending on whether or not the SMMUv3 is enabled and translating addresses
or not.
https://marc.info/?l=linux-crypto-vger&m=151732626428206&w=2
1) A quirk of the hardware revision means we need to turn some elements
off if the iommu is enabled.
2) The device has certain cache related settings that means it needs to know
if it is dealing with VAs or PAs.
Current approach is to see if the iommu_group is set in struct device.
We could fine one instance of another driver doing this and copied that,
(drivers/dma/rcar-dmac.c)
but the precedence is weak enough that confirmation would be good.
So whilst it 'works' the question is whether it is safe in general
and whether there is a better way.
The presence of a group alone is not sufficient, as it only tells you
that the device is associated with an IOMMU in some way (including VFIO
no-iommu mode where said IOMMU isn't even real).
To detect whether translation is active, I think the best way right now
would be to first call iommu_get_domain_for_dev() to see whether the
device is actually attached to a domain, then if so check the domain
type for the __IOMMU_DOMAIN_PAGING flag to confirm if it represents a
translation context rather than a bypass one.
It might be reasonable to propose wrapping that up in an IOMMU API (or
possibly DMA API, as appropriate) helper, as there are certainly other
drivers doing various degrees of this sort of thing for various reasons
(to the point where we currently have to accommodate rather nonsensical
iova_to_phys() calls on identity domains).
Robin.
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