Hi Morimoto-san, On Wednesday 08 Jun 2016 10:05:09 Kuninori Morimoto wrote: > Hi Laurent > # add Niklas > > Sorry for my suport late response. > Thanks Niklas for reminder > > > (With a question for Morimoto-san below) > > (snip) > > > > >> + } while (++i < NR_READS_TO_WAIT); > > > > > > > > How long does the DMA engine typically need to stop ? Is there a safe > > > > upper bound ? > > > > > > I have tested it many times. The highest number of retries was 3 which > > > occurred not very frequently. Normally it is 1-2 > > > > Morimoto-san, could you check with the hardware team if there's a worst > > case guarantee regarding how long the channel could take to stop ? > > You need to wait maximum 0.7ms for it. > both for Gen2/Gen3. > In worst case, it needs 8 request times. > If 1 request is 20,000 cycle > > 20,000cycle x 8request x [4ns/cylce] = 640,000ns > 700us And we're calling the wait function both from interrupt context and from user context with a spinlock held. I'm afraid that's not acceptable, we can't busy- loop for so long with interrupts disabled. -- Regards, Laurent Pinchart -- 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
