On Fri, Jan 22, 2021 at 06:56:19PM +0200, Lauri Kasanen wrote: > On Fri, 22 Jan 2021 16:39:13 +0000 > Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > On Fri, Jan 22, 2021 at 06:23:49PM +0200, Lauri Kasanen wrote: > > > > Your driver can communicate the required alignment using the > > > > blk_queue_update_dma_alignment API. > > > > > > Is it guaranteed to be physically contiguous? > > > > The alignment requirement applies to each bio_vec. > > > > What alignment does the hardware require? > > It requires 8-byte alignment, but the buffer must also be physically > contiguous. Each bio_vec segment is physically contiguous. > I grepped around, but apparently no driver under drivers/block does > direct DMA to the bio buffer. They all use their own buffer and memcpy, > like this patch. ps3vram, ps3disk, amiflop, etc etc. block/brd.c > If all existing drivers use their own buffer, why is a different > approach required for new drivers? It's certainly more efficient to send the data directly to the destination without an unnecessary middle-man. And 64k seems like quite a lot of memory to sequestor considering how little you have to start with.
