On Sun, 20 Jun 2010, David Brownell wrote: > --- On Fri, 6/18/10, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > usb-storage uses the scatter-gather library, which either > > constructs a > > separate URB for each buffer in an SG list, or else passes > > the entire > > list down to the HCD in a single URB (if the HCD supports > > scatterlist operation). > > IMO such low-level details obfuscate the goal... Maybe so, but at some level you have to keep them in mind. Especially if you're not being sufficiently precise about the meaning of terms like "batch", "buffer", and so on. > > > Doesn't the storage driver do exactly that? It builds > > > a single transfer out of multiple buffers. It seems to > > me > > > that we can build a single transfer out of multiple > > > buffers provided all but the last buffers meet some > > > size constraint. > > > > The requirement is that each scatterlist buffer except the > > last must be > > a multiple of the maxpacket length. > > Right; it's been so long since I did that work > that I forgot about those details; sorry; (Plus > the ability to give a scatterlist to an HCD is > pretty new, yes?) Yes; it was introduced within the last year or so. And it is currently supported only by the highest-speed drivers: WHCI, EHCI, and xHCI; there doesn't seem to be much point implementing it for the slower controllers. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
