Messages in this thread | | | Date | Tue, 12 Nov 2013 14:22:47 -0600 | From | Rob Herring <> | Subject | Re: [Xen-devel] [PATCH 2/2] swiotlb-xen: xen_swiotlb_map_page: do not error out if dma_capable fails |
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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
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