Re: [PATCH RFC v3 02/12] iommu: Add a flag to indicate immutable singleton group

[Lu Baolu]

Hi Yi,

On 2022/4/12 14:34, Yi Liu wrote:
> > > > This adds a flag in the iommu_group struct to indicate an immutable
> > > > singleton group, and uses standard PCI bus topology, isolation 
> > > > features,
> > > > and DMA alias quirks to set the flag. If the device came from DT, 
> > > > assume
> > > > it is static and then the singleton attribute can know from the device
> > > > count in the group.
> > >
> > > where does the assumption come from?
> >
> > Hotplug is the only factor that can dynamically affect the
> > characteristics of IOMMU group singleton as far as I can see. If a
> > device node was created from the DT, it could be treated as static,
> > hence we can judge the singleton in iommu probe phase during boot.
>
> not sure if hotplug is the only factor. Is it possible that admin modifies
> the ACS configuration on the bridge?

Not likely. This will completely change the existing iommu_group
settings.

Best regards,
baolu