Commit ed1d08b9 authored by Jean-Philippe Brucker's avatar Jean-Philippe Brucker Committed by Will Deacon
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dt-bindings: Document stall property for IOMMU masters 



On ARM systems, some platform devices behind an IOMMU may support stall,
which is the ability to recover from page faults. Let the firmware tell us
when a device supports stall.

Reviewed-by: default avatarEric Auger <eric.auger@redhat.com>
Reviewed-by: default avatarRob Herring <robh@kernel.org>
Signed-off-by: default avatarJean-Philippe Brucker <jean-philippe@linaro.org>
Link: https://lore.kernel.org/r/20210526161927.24268-2-jean-philippe@linaro.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 19c07b91

Documentation/devicetree/bindings/iommu/iommu.txt

+18 −0
Original line number Diff line number Diff line
@@ -92,6 +92,24 @@ Optional properties: 
  tagging DMA transactions with an address space identifier. By default,

  this is 0, which means that the device only has one address space.



- 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.





Notes:

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