From: robert.jarzmik@free.fr (Robert Jarzmik) Date: Thu, 15 Aug 2013 17:22:14 +0200 Subject: [PATCH 00/20] ARM: pxa: move core and drivers to dmaengine References: <1375889649-14638-1-git-send-email-zonque@gmail.com> <87zjsqzdg8.fsf@free.fr> <52061C53.4050905@gmail.com> <20130814100010.GO32147@intel.com> Message-ID: <8761v7nfmh.fsf@free.fr> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Vinod Koul writes: >> Yes, Vinod and and Dan are certainly the best ones to comment on that I >> think. > I read the file esp the "DMA flow" and "DMA hot chaining timeslice issue". I can > say with "properly" implemented dmaengine driver this is very much doable. Great. > > > Have you guys read: Documentation/dmaengine.txt? Yes. I had not understood the "hot chaining" was implied in it, but now I understand it is part of it, and at the discretion of the slave engine driver. > So for "hot chaning" it would work as follows: > > Client, allocates and channel and prepares the descriptors A B & C > Client (video), submits buffer A, Buffer B. Both are queued by dma driver > Client calls dma_async_issue_pending > DMA driver will start Buffer A. It gets the completetion for A and then Starts > B. It will invoke callbakc for A. > > If you submit C, and invoke dma_async_issue_pending(), C is queued > On B completetion, the DMA driver will start C and invoke callback for B. > > If B completes before C is submitted, after submit and invoking > dma_async_issue_pending(), the C buffer will be queued and started. OK, that settles it then. The API allows hot chaining, and if I understand Daniel's driver properly, he already thought about it (in append_pending_queue()). I have some homework now Daniel, I'll send you my work to include into your patch serie for the review, and my tests of your patches. I need a bit of time (1 or 2 weeks), because of holidays, for my patch. Cheers. -- Robert