On Sat, Feb 19, 2022 at 08:19:00AM +0100, Christoph Hellwig wrote: > On Sat, Feb 19, 2022 at 08:52:21AM +0800, Baoquan He wrote: > > Use dma_alloc_noncoherent() instead of directly allocating buffer > > from kmalloc with GFP_DMA. DMA API will try to allocate buffer > > depending on devices addressing limitation. > > I think it would be better to still allocate the buffer at allocation > time and then just transfer ownership using dma_sync_single* in the I/O > path to avoid the GFP_ATOMIC allocation. This driver allocates the buffer at initialization step and maps the buffer for DMA_TO_DEVICE and DMA_FROM_DEVICE when processing IO. But after making this driver to use dma_alloc_noncoherent(), remapping dma_alloc_noncoherent()-ed buffer is strange So I just made it to allocate the buffer in IO path. At this point I thought we need an API that allocates based on address bit mask (like dma_alloc_noncoherent()), which does not maps buffer into dma address. __get_free_pages/kmalloc(GFP_DMA) has been so confusing.. Hmm.. for this specific case, What about allocating two buffers for DMA_TO_DEVICE and DMA_FROM_DEVICE at initialization time? Thanks, Hyeonggon
