Re: Support SVM without PASID

[Jean-Philippe Brucker <jean-philippe.brucker@arm.com>]

On 11/08/17 07:41, Tian, Kevin wrote:
[...]
>>> Hi Jean,
>>>
>>> I think there is another way to support SVM without PASID.
>>>
>>> Suppose there is a device in the same SOC-chip, the device access memory
>> through SMMU(using internal bus instead of PCIe)
>>> Once page fault, the device send an event with (vaddr, substreamID) to
>> SMMU, then SMMU triggers an event interrupt.
>>>
>>> In the event interrupt handler, we can implement the same logic as PRI
>> interrupt in your patch.
>>> What do you think about that?
>> What you're describing is the SMMU stall model for platform devices. From
>> the driver perspective it's the same as PRI and PASID (SubstreamID=PASID).
>>
>> When a stall-capable device accesses unmapped memory, the SMMU parks
>> the
>> transaction and sends an event marked "stall" on the event queue, with a
>> stall tag (STAG, roughly equivalent to PRG Index). The OS handles the
>> fault and sends a CMD_RESUME command with the status and the STAG.
>> Then
>> the SMMU completes the access or terminates it.
> 
> Can such platform device send multiple SubstreamIDs, or one ID per
> device? 

Yes, SVM-capable platform devices should issue multiple SubstreamIDs and a
single StreamID (equivalent to VT-d's Source-ID).

Thanks,
Jean