On Mon, Aug 24, 2015 at 02:22:49PM +0100, Jon Hunter wrote: > > On 24/08/15 10:22, Vinod Koul wrote: > > On Mon, Aug 24, 2015 at 09:47:13AM +0100, Jon Hunter wrote: > >> > >> On 23/08/15 15:17, Vinod Koul wrote: > >>> On Tue, Aug 18, 2015 at 02:49:09PM +0100, Jon Hunter wrote: > >>> > >>>> @@ -1543,7 +1531,7 @@ static int tegra_dma_pm_suspend(struct device *dev) > >>>> int ret; > >>>> > >>>> /* Enable clock before accessing register */ > >>>> - ret = tegra_dma_runtime_resume(dev); > >>>> + ret = pm_runtime_get_sync(dev); > >>> > >>> why is this required ? > >> > >> Because the clock could be disabled when this function is called. This > >> function saves the DMA context so that if the context is lost during > >> suspend, it can be restored. > > > > Have you verified this? Coz my understanding is that when PM does suspend it > > will esnure you are runtime resume if runtime suspended and then will do > > suspend. > > So you do not need to do above > > I see what you are saying. I did some testing with ftrace today to trace > rpm and suspend/resume calls. If the dma controller is runtime suspended > and I do not call pm_runtime_get_sync() above then I do not see any > runtime resume of the dma controller prior to suspend. Now I was hoping > that this would cause a complete kernel crash but it did not and so the > DMA clock did not appear to be needed here (at least on the one board I > tested). However, I would not go as far as to remove this and prefer to > keep as above. Okay am adding Rafael here for his recommendations. I have tested in past and if my driver was runtime suspended we were resumed prior to being suspended. So I am not sure why you did not see that behaviour, and if that is right we don't need to force resume here -- ~Vinod -- 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
