Re: [PATCH 1/1] iommu/vt-d: Enable PASID during iommu device probe

[Baolu Lu]

On 9/14/22 4:59 PM, Ethan Zhao wrote:
> > > What the error path would be if this code runs on some old platforms 
> > > don't
> > >
> > > support PASID, would you print out "this platform doesn't suppor 
> > > PASID" and
> > >
> > > give users an interface function to query if the PASID cap of iommu 
> > > is enabled
> > >
> > > and if not why ?
> >
> > It's not an error case if the IOMMU doesn't support PASID. But it's an
> > error case if any device drivers call PASID related IOMMU interfaces
> > (for example, iommu_domain_attach/detach_dev_pasid()). The corresponding
> > error code will be returned to the drivers.
> So iommu driver withdraws the flexibility/rights from device driver 
> about the
>
> ability to enable PASID, looks much more *integrated* iommu works as 
> relation

No. This patch doesn't withdraw anything. It's just a code refactoring.

> controller in device-iommu-domain by enabling PASID in iommu probe stage
>
> by default -- iommu decides to enable PASID or not though device-iommu-
>
> domain might not work ? or they should work because they are hard-wired
>
> together (device - iommu) even device is hotpluged later.

I may not get you exactly. :-) Some IOMMU features reply on PASID
capabilities on both IOMMU and device. The IOMMU drivers enumerate the
capabilities and enable them if they are supported.

Best regards,
baolu