netdev - Re: [PATCH] net: fec: fix initial runtime PM refcount

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Date:	Mon, 3 Aug 2015 20:05:39 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	Lucas Stach <l.stach@...gutronix.de>, netdev@...r.kernel.org,
	patchwork-lst@...gutronix.de,
	"David S. Miller" <davem@...emloft.net>, kernel@...gutronix.de,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH] net: fec: fix initial runtime PM refcount

Hello,

I have no clue about runtime-pm, but I added a few people to Cc: who
should know better ...

Best regards
Uwe

On Mon, Aug 03, 2015 at 06:15:54PM +0200, Andrew Lunn wrote:
> On Mon, Aug 03, 2015 at 05:50:11PM +0200, Lucas Stach wrote:
> > The clocks are initially active and thus the device is marked active.
> > This still keeps the PM refcount at 0, the pm_runtime_put_autosuspend()
> > call at the end of probe then leaves us with an invalid refcount of -1,
> > which in turn leads to the device staying in suspended state even though
> > netdev open had been called.
> > 
> > Fix this by initializing the refcount to be coherent with the initial
> > device status.
> > 
> > Fixes:
> > 8fff755e9f8 (net: fec: Ensure clocks are enabled while using mdio bus)
> > 
> > Signed-off-by: Lucas Stach <l.stach@...gutronix.de>
> > ---
> > Please apply this as a fix for 4.2
> > ---
> >  drivers/net/ethernet/freescale/fec_main.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
> > index 32e3807c650e..271bb5862346 100644
> > --- a/drivers/net/ethernet/freescale/fec_main.c
> > +++ b/drivers/net/ethernet/freescale/fec_main.c
> > @@ -3433,6 +3433,7 @@ fec_probe(struct platform_device *pdev)
> >  
> >  	pm_runtime_set_autosuspend_delay(&pdev->dev, FEC_MDIO_PM_TIMEOUT);
> >  	pm_runtime_use_autosuspend(&pdev->dev);
> > +	pm_runtime_get_noresume(&pdev->dev);
> >  	pm_runtime_set_active(&pdev->dev);
> >  	pm_runtime_enable(&pdev->dev);
> 
> This might work, but is it the correct fix?
> 
> Documentation/power/runtime_pm.txt says:
> 
> 534 In addition to that, the initial runtime PM status of all devices is
> 535 'suspended', but it need not reflect the actual physical state of the device.
> 536 Thus, if the device is initially active (i.e. it is able to process I/O), its
> 537 runtime PM status must be changed to 'active', with the help of
> 538 pm_runtime_set_active(), before pm_runtime_enable() is called for the device.
> 
> At the point we call the pm_runtime_ functions above, all the clocks
> are ticking. So according to the documentation pm_runtime_set_active()
> is the right thing to do. But it makes no mention of have to call
> pm_runtime_get_noresume(). I would of expected pm_runtime_set_active()
> to set the count to the correct value.

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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