On Thu, Jun 5, 2025 at 3:37 PM Robin Murphy <robin.mur...@arm.com> wrote: > > On 05/06/2025 8:41 am, Tomeu Vizoso wrote: > [...] > >> In fact this is precisely the usage model I would suggest for this sort > >> of thing, and IIRC I had a similar conversation with the Ethos driver > >> folks a few years back. Running your own IOMMU domain is no biggie, see > >> several other DRM drivers (including rockchip). As long as you have a > >> separate struct device per NPU core then indeed it should be perfectly > >> straightforward to maintain distinct IOMMU domains per job, and > >> attach/detach them as part of scheduling the jobs on and off the cores. > >> Looks like rockchip-iommu supports cross-instance attach, so if > >> necessary you should already be OK to have multiple cores working on the > >> same job at once, without needing extra work at the IOMMU end. > > > > Ok, so if I understood it correctly, the plan would be for each DRM > > client to have one IOMMU domain per each core (each core has its own > > IOMMU), and map all its buffers in all these domains. > > > > Then when a job is about to be scheduled on a given core, make sure > > that the IOMMU for that core uses the domain for the client that > > submitted the job. > > > > Did I get that right? > > It should only need a single IOMMU domain per DRM client, so no faffing > about replicating mappings. iommu_paging_domain_alloc() does need *an* > appropriate target device so it can identify the right IOMMU driver, but > that in itself doesn't preclude attaching other devices to the resulting > domain as well as (or even instead of) the nominal one. In general, not > all IOMMU drivers support cross-instance attach so it may fail with > -EINVAL, and *that*'s when you might need to fall back to allocating > multiple per-instance domains - but as I say since this is a > Rockchip-specific driver where the IOMMU *is* intended to support this > already, you don't need to bother.
Ok, I did just that and it's working great in my testing: I create a domain when the client opens the DRM connection and map all its BOs to it. Then when a job is about to start, I detach whatever domain was attached to the core's group and attach that client's domain. Will send a v7 with it in a couple of days. Thanks! Tomeu
