linux-kernel - Re: [RFT/PATCH] serial: omap: prevent resume if device is not suspended.

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Message-ID: <20120925091112.GK9137@arwen.pp.htv.fi>
Date:	Tue, 25 Sep 2012 12:11:14 +0300
From:	Felipe Balbi <balbi@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Felipe Balbi <balbi@...com>,
	"Poddar, Sourav" <sourav.poddar@...com>,
	gregkh@...uxfoundation.org, khilman@...com, paul@...an.com,
	tony@...mide.com, linux-kernel@...r.kernel.org,
	santosh.shilimkar@...com, linux-serial@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	alan@...ux.intel.com
Subject: Re: [RFT/PATCH] serial: omap: prevent resume if device is not
 suspended.

On Tue, Sep 25, 2012 at 10:12:28AM +0100, Russell King - ARM Linux wrote:
> On Tue, Sep 25, 2012 at 11:31:20AM +0300, Felipe Balbi wrote:
> > On Tue, Sep 25, 2012 at 09:30:29AM +0100, Russell King - ARM Linux wrote:
> > > How is this happening?  I think that needs proper investigation - or if
> > > it's had more investigation, then the results needs to be included in
> > > the commit description so that everyone can understand the issue here.
> > > 
> > > We should not be resuming a device which hasn't been suspended.  Maybe
> > > the runtime PM enable sequence is wrong, and that's what should be fixed
> > > instead?  
> > > 
> > > This sequence in the probe() function:
> > > 
> > >         pm_runtime_irq_safe(&pdev->dev);
> > >         pm_runtime_enable(&pdev->dev);
> > >         pm_runtime_get_sync(&pdev->dev);
> > > 
> > > would enable runtime PM while the s/w state indicates that it's disabled,
> > > and then that pm_runtime_get_sync() will want to resume the device.  See
> > > the section "5. Runtime PM Initialization, Device Probing and Removal"
> > > in Documentation/power/runtime_pm.txt, specifically the second paragraph
> > > of that section.
> > 
> > that was tested. It worked in pandaboard but didn't work on beagleboard
> > XM. Sourav tried to start a discussion about that, but it simply died...
> > 
> > In any case, pm_runtime_get_sync() in probe will always call
> > runtime_resume callback, right ?
> 
> Well, if the runtime PM state says it's suspended, and then you enable
> runtime PM, the first call to pm_runtime_get_sync() will trigger a resume
> attempt.  The patch description is complaining about resume events without
> there being a preceding suspend event.
> 
> This could well be why.

that's most likely, of course. But should we cause a regression to
beagleboard XM because of that ? Also, if you look into chapter 9 of the
runtime_pm documentation, starting on line 822 you'll see documentation
suggests the use of mystruct->is_suspended flag.

-- 
balbi

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