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Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage

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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
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Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage Vinod Koul <vinod.koul@intel.com> - 2015-08-23 16:20 +0200
  Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage Jon Hunter <jonathanh@nvidia.com> - 2015-08-24 10:50 +0200
    Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage Vinod Koul <vinod.koul@intel.com> - 2015-08-24 11:30 +0200
      Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage Jon Hunter <jonathanh@nvidia.com> - 2015-08-24 15:30 +0200
        Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage Vinod Koul <vinod.koul@intel.com> - 2015-08-24 16:20 +0200
          Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-08-25 01:40 +0200
            Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage Jon Hunter <jonathanh@nvidia.com> - 2015-08-25 11:40 +0200
              Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> - 2015-08-26 00:50 +0200
                Re: [RFC PATCH 1/7] DMA: tegra-apb: Correct runtime-pm usage Jon Hunter <jonathanh@nvidia.com> - 2015-08-28 12:40 +0200

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