On Thu, Aug 14, 2014 at 10:53:01AM +0200, Ludovic Desroches wrote: > On Wed, Jul 30, 2014 at 06:03:13PM +0200, Maxime Ripard wrote: > > The dmaengine is neither trivial nor properly documented at the moment, which > > means a lot of trial and error development, which is not that good for such a > > central piece of the system. > > > > Attempt at making such a documentation. > > Good idea, many questions are asked when writing a new dmaengine driver. > > For instance I didn't find how to use the DMA_CTRL_ACK flags. > > - How this flag has to be managed? For instance, async_tx_ack is used in > dmaengine driver but also in some devices. > - Is it mandatory to deal with this flag? It seems some dmaengine > drivers don't care about it. This is one part of the DMA engine API that even I don't understand. It's got something to do with the async engine API, and seems to be something to do with whether a descriptor can have other transactions added to it, and whether a descriptor can be re-used (async-tx engines typically allocate a fixed set of descriptors and recycle them.) I was never able to get to the bottom of what that flag meant or how it should be used with the DMA slave API (and I suspect everyone else just gave up trying to understand it as well.) -- FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
