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. -- 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
