Re: [PATCH v6 03/12] iommu: Add attach/detach_dev_pasid domain ops

[Jason Gunthorpe]

On Tue, May 10, 2022 at 02:17:29PM +0800, Lu Baolu wrote:

> This adds a pair of common domain ops for this purpose and adds helpers
> to attach/detach a domain to/from a {device, PASID}. 

I wonder if this should not have a detach op - after discussing with
Robin we can see that detach_dev is not used in updated
drivers. Instead attach_dev acts as 'set_domain'

So, it would be more symmetrical if attaching a blocking_domain to the
PASID was the way to 'detach'.

This could be made straightforward by following the sketch I showed to
have a static, global blocing_domain and providing a pointer to it in
struct iommu_ops

Then 'detach pasid' is:

iommu_ops->blocking_domain->ops->attach_dev_pasid(domain, dev, pasid);

And we move away from the notion of 'detach' and in the direction that
everything continuously has a domain set. PASID would logically
default to blocking_domain, though we wouldn't track this anywhere.

Jason