Hi Jean-Philippe, On 1/27/21 4:43 PM, Jean-Philippe Brucker wrote: > 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: Rob Herring <robh@xxxxxxxxxx> > Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx> Eric > --- > .../devicetree/bindings/iommu/iommu.txt | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/Documentation/devicetree/bindings/iommu/iommu.txt b/Documentation/devicetree/bindings/iommu/iommu.txt > index 3c36334e4f94..26ba9e530f13 100644 > --- a/Documentation/devicetree/bindings/iommu/iommu.txt > +++ b/Documentation/devicetree/bindings/iommu/iommu.txt > @@ -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: > ====== >
