Messages in this thread | | | Date | Thu, 1 Dec 2011 13:00:46 +1100 | From | David Gibson <> | Subject | Re: [PATCH 1/4] iommu: Add iommu_device_group callback and iommu_group sysfs entry |
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On Thu, Dec 01, 2011 at 12:50:07PM +1100, Benjamin Herrenschmidt wrote: > On Wed, 2011-11-30 at 17:04 -0800, Chris Wright wrote: > > Heh. Put it another way. Generating the group ID is left up to the > > IOMMU. This will break down when there's a system with multiple IOMMU's > > on the same bus_type that don't have any awareness of one another. This > > is not the case for the existing series and x86 hw. > > > > I'm not opposed to doing the allocation and ptr as id (taking care for > > possibility that PCI hotplug/unplug/replug could reuse the same memory > > for group id, however). Just pointing out that the current system works > > as is, and there's some value in it's simplicity (overloading ID == > > group structure + pretty printing ID in sysfs, for example). > > Well, ID can work even with multiple domains since we have domains > numbers. bdfn is 16-bit, which leaves 16-bit for the domain number, > which is sufficient. > > So by encoding (domain << 16) | bdfn, we can get away with a 32-bit > number... it just sucks.
Except that the iommu group structure is not supposed to be specific to PCI.
> Note that on pseries, I wouldn't use bdfn anyway, I would use my > internal "PE#" which is also a number that I can constraint to 16-bits. > > So I can work with a number as long as it's at least an unsigned int > (32-bit), but I think it somewhat sucks, and will impose gratuituous > number <-> structure conversions all over, but if we keep the whole > group thing an iommu specific data structure, then let's stick to the > number and move on with life. > > We might get better results if we kept the number as > > struct iommu_group_id { > u16 domain; > u16 group; > }; > > (Or a union of that with an unsigned int) > > That way the domain information is available generically (can be match > with pci_domain_nr() for example), and sysfs can then be layed out as > > /sys/bus/pci/groups/<domain>/<id> > > Which is nicer than having enormous id's > > Cheers, > Ben. > >
-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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