On Thu, Jul 10, 2014 at 10:49:10AM +0100, Thierry Reding wrote: > On Wed, Jul 09, 2014 at 07:10:48PM +0100, Will Deacon wrote: > > On Wed, Jul 09, 2014 at 03:21:27PM +0100, Thierry Reding wrote: > > > Anything beyond that (e.g. logical grouping of masters) isn't directly > > > within the scope of the binding (it doesn't describe hardware but some > > > policy pertaining to some specific use-case). > > > > This *is* for hardware. I can use PCI as an example, but this could equally > > apply to other types of bus. If you have a bunch of PCI master devices > > sitting being a non-transparent bridge, they can end up sharing the same > > master device ID (requester ID). This means that there is no way in the > > IOMMU to initialise a translation for one of these devices without also > > affecting the others. We currently have iommu_groups to deal with this, but > > it *is* a property of the hardware and we absolutely need a way to describe > > it. I'm happy to add it later, but we need to think about it now to avoid > > merging something that can't easily be extended. > > > > For PCI, the topology is probable but even then, we need this information to > > describe the resulting master device ID emitted by the bridge for the > > upstream group. One way to do this with your binding would be to treat all > > of the upstream masters as having the same device ID. > > Yes, I think that makes most sense. After all from the IOMMU's point of > view requests from all devices behind the bridge will originate from the > same ID. > > So technically it's not really correct to encode the master ID within > each of the devices, but rather they should be inheriting the ID from > the non-transparent bridge. Indeed. Is that possible with your binding, or would we just duplicate the IDs between the masters? > > With virtualisation, we may want to assign a group of devices to a guest but > > without emulating the bridge. This would need something the device-tree to > > describe that they are grouped together. > > But that's also a software decision, isn't it? Virtualization doesn't > have anything to do with the hardware description. Or am I missing > something? Of course I guess you could generate a DTB for the guest and > group device together, in which case you're pretty much free to do what > you want since you're essentially defining your own hardware. If you're doing device passthrough and you want to allow the guest to program the IOMMU, I think that virtualisation is directly related to the hardware description, since the guest will be bound by physical properties of the system. Will -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
