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

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Date:	Tue, 4 Aug 2015 10:20:55 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Lucas Stach <l.stach@...gutronix.de>
cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, Andrew Lunn <andrew@...n.ch>,
	<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

On Tue, 4 Aug 2015, Lucas Stach wrote:

> Am Montag, den 03.08.2015, 14:28 -0400 schrieb Alan Stern:
> > On Mon, 3 Aug 2015, Uwe [iso-8859-1] Kleine-Knig wrote:
> > 
> > > 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?
> > 
> > It looks reasonable to me.  It might also make sense to move all of
> > that pm_runtime_* stuff to the end of the probe routine.  Notice that
> > they don't get undone if register_netdev() fails.
> > 
> Unfortunately we can not move RPM enabling to the end of probe, as the
> MDIO read/write functions that rely on RPM are already called while we
> are still in the middle of the probe function.

In that case, adding a call pm_runtime_get_noresume() is the right 
thing to do.

> I agree that we need better error handling here, but that comment
> applies to the whole FEC probe function. I think that this might be
> invasive enough to justify a delay to the next merge window, not really
> material for the late RCs.

That's entirely up to you, of course.

Alan Stern

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