On Mon, May 12, 2014 at 04:14:12PM +1000, Benjamin Herrenschmidt wrote: > On Mon, 2014-05-12 at 16:10 +1000, Benjamin Herrenschmidt wrote: > > On Mon, 2014-05-12 at 16:00 +1000, David Gibson wrote: > > > I'm not all that impressed by this translation code - in particular > > > the per-bus-type hooks don't make sense to me. AFAIK the > > > interpretation of ranges is not bus specific. I think it will also > > > fail in some cases with #address-cells > 2, which is unfortunate. > > > > > > I'm about to post my own implementation of address translation. > > > > Well, I came up with the original code which did per-bus type hooks. > > There are cases where it is needed. > > > > Take PCI. The top word can contain completely unrelated stuff such > > as the "prefetchable" attribute. > > > > It's perfectly legal to put a prefetchable BAR under a non-prefetchable > > bridge window. > > > > However a translation scheme that doesn't know to know that bit > > will fail. > > Oh and the other way around with IO vs. memory btw. > > > It's not far fetched, it happens on our machines today. > > > > And that's just one of the problems I had back then... > > Note that I'm just stating the problem :-) There may be a better way to > address it. For example, for the one above specifically, well, we could > have a per-bus-type list of masks to apply before translation (bits to > ignore). > > I wish in fact OF had done that to begin with like we have > interrupt-map-mask, maybe we should introduce that concept to limit the > damage to existing well known cases like PCI and have anything new just > tell us what to use for the compare. > > In fact, thinking more, the above mask trick might not fully work for > PCI, we have to check the exact values, because I think the same field > somewhat use an enumeration for 32-bit MEM, 64-bit MEM and IO ... oh > well. Hm, yeah. At this point I'm thinking a per-bus "quirks" mechanism around the basic universal translation logic. -- 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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