[RFC PATCH 24/30] iommu: Specify PASID state when unbinding a task

[Jean-Philippe Brucker]

On 23/03/17 16:52, Joerg Roedel wrote:
> On Thu, Mar 23, 2017 at 03:52:14PM +0000, Jean-Philippe Brucker wrote:
>> On 23/03/17 14:30, Joerg Roedel wrote:
>>> Are you sure about the meaning of the stop-marker? Can you point me to
>>> where it is specified?
>>
>> The concept is introduced in the PCI ECN that adds PASIDs to the ATS
>> specification. I have the following link, which is probably behind a
>> wall:
>>
>> https://pcisig.com/sites/default/files/specification_documents/ECN-PASID-ATS-2011-03-31.pdf
>>
>> A Stop Marker is a PPR with flags Read=Write=0, Last=1, targeting the
>> PASID that is being decommissioned. In section 4.1.2, the specifications
>> details the two device-specific ways of stopping use of a PASID, with or
>> without a Stop Marker. When done with a Stop Marker, the function doesn't
>> have to wait for any outstanding PPR to return, the Stop Marker serves as
>> a PASID barrier.
> 
> Thanks for that, I have a closer look. Is that stopper packet visible to
> software (e.g. is an entry created in the queue)?

As far as I understand, it should be added to the queue like a normal PPR,
and software should check the R/W/L flags combination. For SMMU at least,
it is the same. The only difference is that when the PRI queue overflows,
the SMMU would discard a Stop Marker instead of sending an automated
response to the device (as it would do with others PPR that have the L
flag.) Software shouldn't send a response to a Stop Marker either.

Thanks,
Jean-Philippe