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

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

[Uwe Kleine-König]

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@pengutronix.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/  |

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

[Alan Stern]

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On Mon, 3 Aug 2015, Uwe [iso-8859-1] Kleine-König 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@pengutronix.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.

> > 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.

pm_runtime_set_active() doesn't change the usage count.  All it does is 
set the runtime PM status to "active".

A call to pm_runtime_get_noresume() (or something similar) is necessary
to balance the call to pm_runtime_put_autosuspend() at the end of the
probe routine.  Both the _get_ and the _put_ should be present or
neither should be.

For instance, an alternative way to accomplish the same result is to
replace pm_runtime_put_autosuspend() with pm_runtime_autosuspend().  
The only difference is that the usage counter would not be elevated
during the register_netdev() call, so in theory the device could be
suspended while that routine is running.  But if all the pm_runtime_*
calls were moved to the end of the probe function, even that couldn't
happen.

Alan Stern

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

[Lucas Stach]

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@pengutronix.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.

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.

Regards,
Lucas

-- 
Pengutronix e.K.             | Lucas Stach                 |
Industrial Linux Solutions   | http://www.pengutronix.de/  |

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

[Alan Stern]

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@pengutronix.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

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

[Uwe Kleine-König]

Hello,

On Tue, Aug 04, 2015 at 10:20:55AM -0400, Alan Stern wrote:
> In that case, adding a call pm_runtime_get_noresume() is the right 
> thing to do.
Is this an ack for Lucas' patch?

Best regards
Uwe

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

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

[Alan Stern]

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On Tue, 4 Aug 2015, Uwe [iso-8859-1] Kleine-König wrote:

> Hello,
> 
> On Tue, Aug 04, 2015 at 10:20:55AM -0400, Alan Stern wrote:
> > In that case, adding a call pm_runtime_get_noresume() is the right 
> > thing to do.
> Is this an ack for Lucas' patch?

Yes:

Acked-by: Alan Stern <stern@rowland.harvard.edu>

Alan Stern