Re: [PATCH v2 1/2] PCI: Add PCI device flag PCI_DEV_FLAGS_DMA_ALIAS_ROOT

[Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>]

On 23/06/16 06:01, Jon Masters wrote:
> On 05/11/2016 10:26 AM, Robin Murphy wrote:
>> (I have no actual objection to this patch, though, and at this point
>> I'm just chucking ideas about).
>
> Can I ask what the next steps are here? We're looking for upstream
> direction to guide some internal activities and could really do with
> understanding how you'd like to solve this one longer term as well as
> what interim solution could be acceptable until we get there.

Well, for now I'm planning to leave the explicit "terminate the alias 
walk from the callback function" behaviour in the DT-parsing code[1], 
since there doesn't seem any good reason not to. As Bjorn says, though, 
it probably is generally useful for the PCI code to have its own 
knowledge of exactly where DMA can escape the PCI hierarchy - I now 
wonder if we could actually just do that from the DT/IORT code; if 
firmware says a particular bridge/etc. has a relationship with an ITS or 
SMMU, then presumably it's reasonable to infer that DMA can come out of 
it, thus we could inform the PCI code there and then without it having 
to quirk things on its own?

Robin.

[1]:http://article.gmane.org/gmane.linux.kernel.iommu/13932

>
> Jon.
>