On Tue, Dec 11, 2018 at 06:34:23PM +0000, Jean-Philippe Brucker wrote:
> The cost of enabling those features for a device does seem negligible.
> For the SMMU we need to allocate about 70k of additional memory for the
> initial PASID table, but enabling the PASID cap shouldn't add any
> overhead otherwise. Same for PRI, shouldn't add any overhead.
Okay, the memory requirements are a pretty good case for an
enable/disable part in the API.
> As for ATS, it supposedly makes things faster, although it does mean
> more invalidation requests. There currently is a global pci=noats
> parameter, but maybe we need something with finer granularity to
> enable/disable it per device?
Yeah, I don't object against this, but I think this is a matter of PCI
code. The IOMMUs should just enable ATS when it is available. PCI core
can fail to enable it if requested by the user.
Regards,
Joerg
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