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? Can you say more about this? >> 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.) (FWIW, both the NFC and the MBUS agent are custom designs, not third-party IP blocks.) Regards. -- 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
