On Mon, Sep 22, 2003 at 10:13:26AM -0500, Bret Indrelee wrote: > > Are there alignment restrictions on the address boundry your can > start a DMA with when using the pci_map_single() / pci_unmap_single() > calls? > > For some reason, I thought they had to be cache line aligned, but when > I went back through the documentation I couldn't find any such > restriction.
cache line alignment is an unwritten requirement that hasn't yet been addressed in DMA-mapping.txt. Unfortunately, kmalloc() doesn't guarantee this so it's necessary to overallocate and align. You can use L1_CACHE_BYTES for this. Roland Dreier had a patch which added a little helper for this stuff as well as docs. Unfortunately, it's been dropped on the floor until somebody with interest and time in non-coherent platforms picks it up. http://lwn.net/Articles/2482/ -Matt ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/