Hi Chris, On 2017-10-27 21:11:39 +0000, Chris Brandt wrote: > Hi Wolfram, > > Sorry, back on this subject... > > > > > [<bf9921e7>] (tmio_mmc_dma_callback) from [<bf908e1b>] > > > (rzadma_tasklet+0x23/0x98) > > > > > > For SYS-DMAC, this is a callback called by the dmaengine core once the > > > DMA is completed. My guess is you call it directly from an interrupt > > > handler? It would be easier to talk over code here, I guess. > > > > > > > Is it now a requirement that I have to register my DMA channel > > > > interrupts as devm_request_threaded_irq? > > > > > > > > Will that fix my issue? > > > > > > I can't say yet if this alone will do. Likely not. Can you share the > > > code already? > > > > The interrupt handler is starting a tasklet, and then the tasklet calls > > the callback. I thought tasklets didn't run in an interrupt context????? > > > So here's what I found. > > According to: > > https://www.kernel.org/doc/Documentation/dmaengine/client.txt > > It says: > "Note that callbacks will always be invoked from the DMA engines > tasklet, never from interrupt context." > > > My DMA driver was calling the SDHI callback from within a tasklet (ie, > softirq). Almost all the other DMA drivers doing the same thing. > > All was fine until that patch you submitted (52ad9a8e854c) that now adds > a wait_for_completion() in the SDHI callback. This is a interesting finding, I did some bisecting a while back to try and understand why a known problematic SD card started to have more issues then last time I tested it. That investigation also ended up pointing to 52ad9a8e854c. > > Now I get the "BUG: scheduling while atomic". > > The R-Car driver uses a threaded irq to call the callbacks, not a > tasklet. > > So I hacked my code to also call the callbacks from a threaded irq like > rcar-dma.c. > And....that works (no more scheduling while atomic). Can you post that hack or just send it to me privately if it's to hackish for a mailinglist :-) I'm still interested in my problematic SD card and would just like to see what happens with your hack applied. > > So, the question is, which of these statements are correct? > > 1. wait_for_completion should not be called in a DMA callback > > 2. DMA engine drivers should use threaded IRQs instead of tasklets > > > The issue with #2 is that mic_x100_dma.c, sh/rcar-dmac.c and > sh/shdma-base.c are the only ones calling request_threaded_irq, > so you would think that tasklets are the correct method. > > > Thanks, > Chris > -- Regards, Niklas Söderlund -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
