On 25/08/15 01:04, Rafael J. Wysocki wrote: > On Monday, August 24, 2015 07:51:43 PM Vinod Koul wrote: >> 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. > > Well, and what is the question I'm supposed to answer, exactly? > > I was in Seattle last week, so haven't been following this closely. > >> 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 > > We're adding code for skipping runtime-resume-before-system-suspend, because > it is not desirable in general. > > The rule of thumb is that if you know you need to change the device's settings > (eg. because of wakeup being enabled or not) for system suspend and that > requires the device to be resumed, resume it. It can stay suspended > otherwise. Thanks Rafael. Vinod, thinking about this some more, I am wondering if it is just better to get rid of the suspend/resume callbacks and simply handling the state in the runtime suspend/resume callbacks. I think that would be safe too, because once the clock has been disabled, then who knows what the context state will be. Cheers Jon -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
