Re: [PATCH v14 10/10] iommu/arm-smmu-v3: Add stall support for platform devices

Will Deacon
2021-04-01T17:55:58Z

On Thu, Apr 01, 2021 at 05:47:19PM +0200, Jean-Philippe Brucker wrote:
> The SMMU provides a Stall model for handling page faults in platform
> devices. It is similar to PCIe PRI, but doesn't require devices to have
> their own translation cache. Instead, faulting transactions are parked
> and the OS is given a chance to fix the page tables and retry the
> transaction.
>
> Enable stall for devices that support it (opt-in by firmware). When an
> event corresponds to a translation error, call the IOMMU fault handler.
> If the fault is recoverable, it will call us back to terminate or
> continue the stall.

Which hardware is this useful for? Stalling adds a fair amount of complexity
to the driver, so I don't think we should support it unless we're likely to
see platforms that both implement it and do something useful with it.

Will