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. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
