On 07/23/2012 05:20 PM, Benjamin Herrenschmidt wrote: > On Mon, 2012-07-23 at 11:17 -0500, Scott Wood wrote: >>> This is wrong. >> >> How so? >> >>> Don't you have an iommu do deal with those devices anyway ? >> >> Yes, but we don't yet have DMA API support for it, it would lower >> performance because we'd have to use a lot of subwindows which are >> poorly cached (and even then we wouldn't be able to map more than 256 >> pages at once on a given device), and the IOMMU may not be available at >> all if we're being virtualized. > > Ugh ? You mean some designers need to be fired urgently and wasted > everybody's time implementing an unusable iommu ? Nice one ...
Yeah, that's old news. It's somewhat usable for specific purposes, using very large pages, but not for arbitrary use. >>> But even then, I'm dubious this is really needed. >> >> We'd like our drivers to stop crashing with more than 4GiB of RAM on 64-bit. > > Fix your HW :-) I wish... Some hardware people may solicit input from us every now and again, but ultimately they do what they want. Returning addresses in excess of a device's declared DMA mask is something that needs fixing too, though. -Scott _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
