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

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Date:	Wed, 4 Nov 2015 14:04:38 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Kevin Hilman <khilman@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Jon Hunter <jonathanh@...dia.com>,
	Laxman Dewangan <ldewangan@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	dmaengine@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] dmaengine: tegra-apb: Correct runtime-pm usage

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

-- 
~Vinod
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