On Thu, Dec 10, 2015 at 04:46:24PM -0800, Christoph Hellwig wrote: > On Thu, Dec 10, 2015 at 05:29:50PM -0700, Jason Gunthorpe wrote: > > Hrm.. sizeof(void *) > sizeof(dma_addr_t) seemed pretty obscure to me, > > here is the original discussion: > > > > https://lkml.org/lkml/2006/12/13/245 > > > > Sounds like someone was worried about sparc64. I doubt it is an actual > > issue today, but granted the u64 did make some sense. > > sparc64 still uses a 32-bit dma_addr_t.
Hmm, too bad, that choice severly compromises the rdma userspace - user space can't create mrs that exceed 4G in total :( > > So, I *believe* the issue is that linux has (had?) no approved way to > > convert from a device specific dma_addr_t to a virtual address. > > Linux doesn't have an approved way because it's impossible for the > generic case. When you have an iommu you have potentially multiple > page tables mapping physical addresses to device virtual addresses, > and there is no easy way to do a reverse mapping. Yes, I know > > It is really too bad we can't just use get_dma_ops to handle this case > > and instead require our own infrastructure. > > FYI, I have a patch series in linux-next to switches all remaining > architectures to use get_dma_ops, and there are plans to allow generic > per-device dma_ops based on that. Great, so once that is merged we can drop the ib_* versions of all this and just have qib/etc customize get_dma_ops? Other than the dma_addr_t size issue that sounds great.. Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
