On Tue, Mar 28, 2023 at 02:43:03PM +0200, Petr Tesarik wrote: > Oh, wait! I can do at least something for devices which do not use > swiotlb at all. > > If a device does not use bounce buffers, it cannot pass an address > that belongs to the swiotlb. Consequently, the potentially > expensive check can be skipped. This avoids the dynamic lookup > penalty for devices which do not need the swiotlb. > > Note that the counter always remains zero if dma_io_tlb_mem is > NULL, so the NULL check is not required. Hmm, that's yet another atomic for each map/unmap, and bloats struct device. (Btw, in case anyone is interested, we really need to get started on moving the dma fields out of struct device into a sub-struct only allocated for DMA capable busses)
