Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx> writes: > On Fri, Nov 25, 2016 at 02:03:20PM +0000, Måns Rullgård wrote: >> Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx> writes: >> >> > On Fri, Nov 25, 2016 at 01:50:35PM +0000, Måns Rullgård wrote: >> >> Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx> writes: >> >> > It would be unfair to augment the API and add the burden on everyone >> >> > for the new API when 99.999% of the world doesn't require it. >> >> >> >> I don't think making this particular dma driver wait for the descriptor >> >> callback to return before reusing a channel quite amounts to a horrid >> >> hack. It certainly wouldn't burden anyone other than the poor drivers >> >> for devices connected to it, all of which are specific to Sigma AFAIK. >> > >> > Except when you stop to think that delaying in a tasklet is exactly >> > the same as randomly delaying in an interrupt handler - the tasklet >> > runs on the return path back to the parent context of an interrupt >> > handler. Even if you sleep in the tasklet, you're sleeping on behalf >> > of the currently executing thread - if it's a RT thread, you effectively >> > destroy the RT-ness of the thread. Let's hope no one cares about RT >> > performance on that hardware... >> >> That's why I suggested to do this only if the needed delay is known to >> be no more than a few bus cycles. The completion callback is currently >> the only post-transfer interaction we have between the dma and device >> drivers. To handle an arbitrarily long delay, some new interface will >> be required. > > And now we're back at the point I made a few emails ago about undue > burden which is just about quoted above... So what do you suggest? Stick our heads in the sand and pretend everything is perfect? -- 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
