Mason <slash.tmp@xxxxxxx> writes: > On 24/11/2016 15:17, Måns Rullgård wrote: > >> Mason wrote: >> >>> [ 35.085854] SETUP DMA >>> [ 35.088272] START NAND TRANSFER >>> [ 35.091670] tangox_dma_pchan_start from tangox_dma_irq >>> [ 35.096882] tango_dma_callback from vchan_complete >>> [ 45.102513] DONE FAKE SPINNING >>> >>> So the IRQ rolls in, the ISR calls tangox_dma_pchan_start, >>> which calls tangox_dma_pchan_detach to tear down the sbox >>> setup; and only sometime later does the DMA framework call >>> my callback function. >> >> Yes, I realised this soon after I said it. The dma driver could be >> rearranged to make it work though. > > There is a way to make the tasklet run and invoke the callback > before the interrupt service routine proceeds? No, but it would be possible to defer the teardown to the tasklet. Having said that, I'm not sure it's such a great idea since the tasklet could be held up for an arbitrary length of time waiting for the target to finish. >>> So far, the work-arounds I've tested are: >>> >>> 1) delay sbox tear-down by 10 µs in tangox_dma_pchan_detach. >>> 2) statically setup sbox in probe, and never touch it henceforth. >>> >>> WA1 is fragile, it might break for devices other than NFC. >>> WA2 is what I used when I wrote the NFC driver. >>> >>> Can tangox_dma_irq() be changed to have the framework call >>> the client's callback *before* tangox_dma_pchan_start? >>> >>> (Thinking out loud) The DMA_PREP_INTERRUPT requests that the >>> DMA framework invoke the callback from tasklet context, >>> maybe a different flag DMA_PREP_INTERRUPT_EX can request >>> calling the call-back directly from within the ISR? >>> >>> (Looking at existing flags) Could I use DMA_CTRL_ACK? >>> Description sounds like some kind hand-shake between >>> client and dmaengine. >>> >>> Grepping for DMA_PREP_INTERRUPT, I don't see where the framework >>> checks that flag to spawn the tasklet? Or is that up to each >>> driver individually? >> >> Those flags all have defined meanings and abusing them for other things >> is a bad idea. As far as possible, device drivers should work with any >> dma driver. > > I was asking about introducing a new flag, not abusing existing > flags. (I don't understand the semantics of DMA_CTRL_ACK.) This needs more than a new flag anyhow. > (FWIW, both the NFC and the MBUS agent are custom designs, > not third-party IP blocks.) Sure, but who knows what will be in the next chip? -- Måns Rullgård -- 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
