Re: [PATCH v3 04/15] iommu: Move bus setup to IOMMU device registration

[Robin Murphy]

On 2022-07-07 07:51, Tian, Kevin wrote:
> > From: Robin Murphy <robin.murphy@xxxxxxx>
> > Sent: Wednesday, July 6, 2022 1:08 AM
> >
> > @@ -202,12 +210,32 @@ int iommu_device_register(struct iommu_device
> > *iommu,
> >   	spin_lock(&iommu_device_lock);
> >   	list_add_tail(&iommu->list, &iommu_device_list);
> >   	spin_unlock(&iommu_device_lock);
> > +
> > +	for (int i = 0; i < ARRAY_SIZE(iommu_buses); i++) {
> > +		struct bus_type *bus = iommu_buses[i];
> > +		int err;
> > +
> > +		if (bus->iommu_ops && bus->iommu_ops != ops) {
> > +			err = -EBUSY;
> > +		} else {
> > +			bus->iommu_ops = ops;
> > +			err = bus_iommu_probe(bus);
> > +		}
> > +		if (err) {
> > +			iommu_device_unregister(iommu);
> > +			return err;
> > +		}
> > +	}
> > +
>
> Probably move above into a new function bus_iommu_probe_all():
>
> 	/* probe all buses for devices associated with this iommu */
> 	err = bus_iommu_probe_all();
> 	if (err) {
> 		iommu_device_unregister(iommu);
> 		return err;
> 	}
>
> Just  my personal preference on leaving logic in iommu_device_register()
> more relevant to the iommu instance itself.

On reflection I think it makes sense to pull the 
iommu_device_unregister() out of the loop anyway - I think that's really 
a left-over from between v1 and v2 when that error case briefly jumped 
to another cleanup loop, before I realised it was actually trivial for 
iommu_device_unregister() to clean up for itself.

However I now see I've also missed another opportunity, and the -EBUSY 
case should be hoisted out of the loop as well, since checking 
iommu_buses[0] is sufficient. Then it's hopefully much clearer that once 
the bus ops go away we'll be left with just a single extra line for the 
loop, as in iommu_device_unregister(). Does that sound reasonable?

> Apart from that:
>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

Thanks! (and for the others as well)

Robin.