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. Furthermore, other drivers do similar things, including the sirf dma controller (see sirf-dma.c). Cheers Jon -- 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
