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

[Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>]

On Thu, Mar 23, 2017 at 05:03:46PM +0000, Jean-Philippe Brucker wrote:
> On 23/03/17 16:52, Joerg Roedel wrote:
> > 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.

The document you posted is an addition to the spec, so we can't rely on
a stop marker being sent by a device when it shuts down a context.
Current AMD GPUs don't send one, afaik.

I think the best we can do is shutting down processing for this PASID
when and inform the device driver, when we receive a stop marker. An
additional, optional call-back would do the job.



	Joerg