linux-kernel - Re: [PATCH] dmaengine: edma: Remove dynamic TPTC power management feature

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Date:	Thu, 28 Jan 2016 09:11:46 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	vinod.koul@...el.com, dan.j.williams@...el.com,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	nsekhar@...com, t-kristo@...com
Subject: Re: [PATCH] dmaengine: edma: Remove dynamic TPTC power management
 feature

* Peter Ujfalusi <peter.ujfalusi@...com> [160128 01:01]:
> On 01/27/2016 05:54 PM, Tony Lindgren wrote:
> > * Peter Ujfalusi <peter.ujfalusi@...com> [160127 01:12]:
> >> The dynamic or on demand pm_runtime does not work correctly on am335x and
> >> am437x due to interference with hwmod.
> > 
> > Hmm care expand a bit what is the problem with this "interference"?
> 
> The idea was to enable/power on only the TPTCs which is actually in use and
> leave the unused ones off. Which is is nice and all, but...
> The original implementation did the pm_runtime calls for the tptcs from the
> edma tpcc driver instance and the main issue was that I did the pm_runtime
> calls in the edma-tpcc pm callbacks as well.
> Since omap hwmod/device also handles pm_runtime on behalf of the drivers we
> got nasty issues, kernel crash, warnings on suspend/resume.
> 
> Then I did implemented the on demand power management in a totally different
> way, still keeping only tptcs enabled which is in use.
> In this way all the omap hwmod/device incoherency was gone and things looked
> fine, but it turned out that on second suspend we are not able to wake up the
> board.
> I and Tero debugged this a bit and it turns out that we need to kepp all tptcs
> enabled and powered, otherwise the HW will not going to be able to complete
> the transition, breaking suspend/resume.

Probably you only need to keep the tptcs being used enabled though? They
should be completely independent otherwise?

> With pm_runtime_enable() + get_sync() on all tptcs we can suspend and resume
> w/o problems and they will be disabled/enabled by omap hwmod/device code,
> following nicely the power state of the system.
> 
> As a note: I did tried the suspend/resume with the old code with dra7, but it
> turned out that on dra7 SW has no control over the tptc power state, it
> follows the system in HW.
> 
> In short: The implementation was flawed and even if the implementation is
> correct the HW will lock up if we do on demand tptc power management.

OK interesting.

Regards,

Tony