Re: [PATCH 1/6] dmaengine: tegra-apb: Correct runtime-pm usage

From: Vinod Koul
Date: Wed Nov 04 2015 - 03:31:27 EST

On Tue, Nov 03, 2015 at 01:25:09PM -0800, Kevin Hilman wrote:
> >>>>> /* Enable clock before accessing register */
> >>>>> - ret = tegra_dma_runtime_resume(dev);
> >>>>> + ret = pm_runtime_get_sync(dev);
> >>>>
> >>>> If you are runtime suspended then core will runtime resume you before
> >>>> invoking suspend, so why do we need this
> >>>
> >>> Is this change now in the mainline? Do you have commit ID for that?
> >>>
> >>> I recall the last time we discussed this that Rafael said that they were
> >>> going to do that, but he said as a rule of thumb if you need to resume
> >>> it, resume it [0].
> >>
> >> IIRC this has been always the behaviour, at least I see this when I test the
> >> devices
> >
> > I have been doing some testing today and if the DMA is runtime
> > suspended, then I don't see it runtime resumed before suspend is called.
> >
> > Can you elborate on "at least I see this when I test the devices"? What
> > are you looking at? Are you using kernel function tracers in some way?
> The PM core does a _get_noresume()[1] which tries to prevent runtime
> suspends *during* a system suspend. However, the PM core should not be
> doing an actual runtime resume of the device, so if the device is
> already runtime suspended, it will not be runtime resumed by the core,
> so if the driver needs it to be runtime resumed, it needs to do it
> itself.

+ Rafael

This is contrariry to what I see, If my driver is runtime suspended and on
suspend, it gets runtime resumed and then suspended

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