On Thu, 2009-05-21 at 16:18 -0400, Jeremy Fitzhardinge wrote: > I guess the test is checking for a bad implementation of map_single().
More importantly the io_tlb_overflow_buffer is basically a second chance if you exhaust the swiotlb pool. The check seems to be there to ensure that the second chance memory is suitable for the device (it's hard to imagine, but possible I suppose, that it wouldn't be), a bad implementation of map_single() is a secondary concern I suspect. If all the callers of map_page did proper error handling this would all be unnecessary. I guess someone was worried, at least at one point, that they didn't. The failure case could possibly be scribbling into a random memory location or more worryingly sprinkling random memory locations onto your disk or whatever. That said I'd imagine that map_page returning NULL would cause an oops long before anything tried to DMA anything and the second chance probably doesn't buy us much in practice. Ian. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
