Re: [PATCH v3 04/15] iommu: Move bus setup to IOMMU device registration

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On 2022/7/6 22:37, Robin Murphy wrote:
On 2022-07-06 03:35, Baolu Lu wrote:
On 2022/7/6 01:08, Robin Murphy wrote:
@@ -202,12 +210,32 @@ int iommu_device_register(struct iommu_device *iommu,
      spin_lock(&iommu_device_lock);
      list_add_tail(&iommu->list, &iommu_device_list);
      spin_unlock(&iommu_device_lock);
+
+    for (int i = 0; i < ARRAY_SIZE(iommu_buses); i++) {
+        struct bus_type *bus = iommu_buses[i];
+        int err;
+
+        if (bus->iommu_ops && bus->iommu_ops != ops) {
+            err = -EBUSY;
+        } else {
+            bus->iommu_ops = ops;
+            err = bus_iommu_probe(bus);
+        }
+        if (err) {
+            iommu_device_unregister(iommu);
+            return err;
+        }
+    }
+
      return 0;
  }
  EXPORT_SYMBOL_GPL(iommu_device_register);

With bus_set_iommu() retired, my understanding is that now we embrace
the first-come-first-serve policy for bus->iommu_ops setting. This will
lead to problem in different iommu_ops for different bus case. Did I
overlook anything?

This is just formalising the de-facto situation that we don't actually have any combination of drivers that could load on the same system without already attempting to claim at least one bus in common. It's also only temporary until the bus ops are removed completely and we fully support multiple drivers coexisting, which only actually takes a handful more patches - I've realised I could even bring that change *ahead* of the big job of converting iommu_domain_alloc() (I'm not convinced that the tree-wide flag-day patch for that I currently have in the dev branch is really viable, nor that I've actually got the correct device at some of the callsites), although whether it's worth the potentially-surprising behaviour that might result I'm less sure.

If we already had systems where in-tree drivers successfully coexisted on different buses then I'd have split this up and done something a bit more involved to keep a vestigial bus_set_iommu() around until the final bus ops removal, but since we don't, it seemed neatest to do all the related work in one go.

Fair enough. I've never seen a mixed system as far. It's fine for us to
retire bus_set_iommu() for now and then formally support mixed IOMMU
drivers later.

Best regards,
baolu



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