On Tue, 12 Nov 2013, Rob Herring wrote: > On 11/12/2013 11:27 AM, Stefano Stabellini wrote: > > Russell gave a great explanation of the issue so I am just going to > > limit myself to answering to: > > > > On Tue, 12 Nov 2013, Konrad Rzeszutek Wilk wrote: > >>> Considering that we know that the swiotlb buffer has a low address, > >>> skip the check. > >> > >> I am not following that sentence. Could you please explain to me > >> how the SWIOTLB buffer low address guarantees that we don't need > >> the check? > > > > xen_swiotlb_fixup makes sure that the swiotlb buffer is lower than 4GB, > > probably lower than 3GB, by passing dma_bits to > > xen_create_contiguous_region. > > This meets the requirements of most devices out there. > > In fact we are not even running this check under the same conditions in > > swiotlb_map_sg_attrs. > > I admit that it is possible to come up with a scenario where the check > > would be useful, but it is far easier to come up with scenarios where > > not only is unneeded but it is even harmful. > > > > Alternatively (without Rob's "of: set dma_mask to point to > > coherent_dma_mask") Linux 3.13 is going to fail to get the network > > running on Midway. It is going to avoid fs mounting failures just > > because we don't do the same check in swiotlb_map_sg_attrs. > > > > FYI given that Rob's patch is probably going upstream soon anyway, I > > don't feel so strongly about this. > > It is in Linus' tree now. OK, I'll drop this patch then. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/