On 02/04/2013 04:11 PM, Linus Walleij wrote: > On Mon, Feb 4, 2013 at 9:33 PM, Mark Brown > <broo...@opensource.wolfsonmicro.com> wrote: >> On Mon, Feb 04, 2013 at 09:29:46PM +0100, Linus Walleij wrote: >>> On Mon, Feb 4, 2013 at 8:22 PM, Cyril Chemparathy <cy...@ti.com> wrote: >> >>>> Based on our experience with fitting multiple subsystems on top of this >>>> DMA-Engine driver, I must say that the DMA-Engine interface has proven >>>> to be a less than ideal fit for the network driver use case. >> >>>> The first problem is that the DMA-Engine interface expects to "push" >>>> completed traffic up into the upper layer as a part of its callback. >>>> This doesn't fit cleanly with NAPI, which expects to "pull" completed >>>> traffic from below in the NAPI poll. We've somehow kludged together a >>>> solution around this, but it isn't very elegant. >> >>> I cannot understand the actual technical problem from the above >>> paragraphs though. dmaengine doesn't have a concept of pushing >>> nor polling, it basically copies streams of words from A to B, where >>> A/B can be a device or a buffer, nothing else. >> >>> The thing you're looking for sounds more like an adapter on top >>> of dmaengine, which can surely be constructed, some >>> drivers/dma/dmaengine-napi.c or whatever. >> >> Broadly speaking what NAPI wants is to never get any callbacks from the >> hardware (or DMAs). It wants to wake up periodically, take a look at >> what packets have been read by the hardware and process them. The goal >> is to have the DMAs sitting and running without disturbing the processor >> at all after the first packet has been handled. > > OK we should definately be able to encompass that in dmaengine > quite easily. > > So I think the above concerns are moot. The callback we can > set on cookies is entirely optional, and it's even implemented by > each DMA engine, and some may not even support it but *require* > polling, and then it won't even be implemented by the driver. > > Which probably stems from the original design of the dmaengine > API, which was for TCP networking acceleration, mainly. > > Cyril, just stack up the cookies and take a sweep over them to see > which ones are baked when the NAPI poll comes in -> problem > solved. >
You're assuming that cookies complete in order. That is not necessarily true. Thanks -- Cyril. ------------------------------------------------------------------------------ Free Next-Gen Firewall Hardware Offer Buy your Sophos next-gen firewall before the end March 2013 and get the hardware for free! Learn more. http://p.sf.net/sfu/sophos-d2d-feb _______________________________________________ spi-devel-general mailing list spi-devel-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/spi-devel-general
