@@ -86,6 +86,30 @@ have a means to turn off translation. But it is invalid in such cases to
 disable the IOMMU's device tree node in the first place because it would
 prevent any driver from properly setting up the translations.
 
+Optional properties:
+--------------------
+- dma-can-stall: 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.
+
+- pasid-bits: 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.
+
 
 Notes:
 ======