schemas: Add IOMMU consumer "pasid-num-bits" and "dma-can-stall" prop…

…erties

Add optional IOMMU consumer properties. These are copied from
Documentation/devicetree/bindings/iommu/iommu.txt in the Linux kernel.

Descriptions were written by Jean-Philippe Brucker.

Co-developed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>

dtschema/schemas/iommu/iommu.yaml

@@ -17,4 +17,30 @@ properties:
   iommus:
     $ref: /schemas/types.yaml#/definitions/phandle-array
 
+  pasid-num-bits:
+    description:
+      Some masters support multiple address spaces for DMA, by tagging DMA
+      transactions with an address space identifier. By default, this is 0,
+      which means that the device only has one address space.
+    default: 0
+
+  dma-can-stall:
+    type: boolean
+    description: >
+      When present, the master can wait for a transaction to complete for an
+      indefinite amount of time. Upon translation fault some IOMMUs, instead of
+      aborting the translation immediately, may first notify the driver and keep
+      the transaction in flight. This allows the OS to inspect the fault and,
+      for example, make physical pages resident before updating the mappings and
+      completing the transaction. Such IOMMU accepts a limited number of
+      simultaneous stalled transactions before having to either put
+      back-pressure on the master, or abort new faulting transactions.
+
+      Firmware has to opt-in stalling, because most buses and masters don't
+      support it. In particular it isn't compatible with PCI, where transactions
+      have to complete before a time limit. More generally it won't work in
+      systems and masters that haven't been designed for stalling. For example
+      the OS, in order to handle a stalled transaction, may attempt to retrieve
+      pages from secondary storage in a stalled domain, leading to a deadlock.
+
 additionalProperties: true