On Thu, 1 Feb 2018 12:49:24 +0000 Robin Murphy <robin.mur...@arm.com> wrote:
> 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. Thanks - that works great. > > 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). Sounds like a good plan but the fun question as ever is what to call it.. iommu_domain_can_map or iommu_domain_is_translating perhaps? For now I'll just put the check in the driver so we can move forward in parallel. Thanks, Jonathan > > Robin. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
