Re: [RFC PATCH 0/5] iommu/arm-smmu-v3: Implement Runtime/System Sleep ops

[Jason Gunthorpe <jgg@ziepe.ca>]

On Wed, Mar 19, 2025 at 12:42:49AM +0000, Pranjal Shrivastava wrote:

> 3. Invoking runtime_pm_get/put
> Given that most of the configuration done by arm-smmu-v3 is stored in
> memory, the initial idea is to focus on areas where the driver accesses
> the hw via exposed ops, like iommmu_ops, iommu_flush_ops, sva_ops etc.

This seems weird, if the SMMU is suspended doesn't it also fail DMA
transactions? Why would ops like flush even be called if the HW is
disabled?

flush is performance path stuff, so it doesn't seem great to be adding
extra calls there.

> Instead of wrapping every exposed op with an rpm_get/put, the idea is to
> follow through till a logical common point (lowest common ancestor in
> the call hierarchies) and wrap those with the rpm_get/put calls.

Should the iommu core be doing this instead of hidden in drivers? It
seems like there might be better information there about when we
expect the IOMMU to be powered up and working and when it is OK to
have it shutdown?

And maybe in this direction we can do things like remove the
translation before doing a suspend so that flush ops are not a
problem.

Jason