On Sun, Jan 18, 2004 at 08:50:06PM +0100, Dimitri Torfs wrote: > dma_map_single() is supposed to be called on a buffer that exactly > starts and ends on a cacheline boundary, otherwise "bad things" > (e.g. overwrite of data that was written by device, ...) (especially > on dma non-coherent systems) may happen. > > So what should be done when dma_map_single is not called > with a sane (ptr, size) argument ? > > - is the driver (caller) considered buggy and should we return a 0 > return-value ? > - is the driver (caller) considered buggy but we do the mapping > anyway, hoping that the driver has not/will not touched/touch > the boundary cachelines ? The driver is considered buggy; dma_map_single's behaviour is undefined so it's perfectly ok if it paints neighbour's cat pink ;-) > - should we take appropriate actions to make sure the > cache-effects do not come into play (e.g. by using some kind of > bounce buffer) ? Technically bounce buffers can be handled inside dma_map_single & co but it's not a good idea. Better set the appropriate flags so higher levels can allocate memory with the appropriate GFP_* flags and thereby hopefully avoid overly frequent buffer bouncing. Ralf
