On Fri, Nov 09, 2018 at 03:12:34PM -0800, David Miller wrote: > But patch #2 on the other hand, not so much. > > I hate seeing values returned by reference, it adds cost especially > on cpus where all argments and return values fit in registers (we end > up forcing a stack slot and memory references). > > And we don't need it here. > > DMA addresses are like pointers, and therefore we can return errors and > valid success values in the same dma_addr_t just fine. PTR_ERR() --> DMA_ERR(), > IS_PTR_ERR() --> IS_DMA_ERR, etc. In the end this is an inline function, so with a decently smart compiler the generated code shouldn't change too much. The big problem that prompted me to come up with this patch is that not handling failure from dma_map* in a swiotlb setup can lead to grave data corruption, and we have no easy way to force error checking on these return values. I've added a few of the static typechecking suspect if they have a better idea on how to make the return value of dma_map_single/pages in a way that we get warnings if dma_mapping_error isn't called on them. But I can't really think of a good way.
