On Tue, 2008-02-26 at 16:47 +1100, Benjamin Herrenschmidt wrote: > On Tue, 2008-02-26 at 00:43 -0500, Mark Lord wrote: > > > I suppose so. I don't remember all of the details, but iirc, it has to > > > do with crossing 64K boundaries. Some controllers can't handle it. > > > > > > It's not only the _size_ of the segments, it's their alignment. > > > > > > The iommu will not keep alignement beyond the page size (and even > > > then... on powerpc with a 64k base page size, you may still end up with > > > a 4k aligned result, but let's not go there now). > > .. > > > > That's just not possible, unless the IOMMU *splits* segments. > > And the IOMMU experts here say that it never does that. > > It is totally possible, and I know as wrote part of the powerpc iommu > code :-) > > The iommu code makes no guarantee vs. preserving the alignment of a > segment, at least not below PAGE_SIZE. It's supposed to, precisely to forestall this case. The alignment guarantees of the parisc iommu code are sg length aligned up to a fixed maximum (128k on 32 bit and 256k on 64 bit because of the way the allocator works). However, tomo's code is fixing this, so it shouldn't be a problem much longer. James - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
