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... -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- 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
