On Fri, 27 Jul 2012, Rafael J. Wysocki wrote:

> On Friday, July 27, 2012, Alan Stern wrote:
> > On Fri, 27 Jul 2012, Huang Ying wrote:
> > 
> > > --- a/drivers/pci/pci-driver.c
> > > +++ b/drivers/pci/pci-driver.c
> > > @@ -280,8 +280,12 @@ static long local_pci_probe(void *_ddi)
> > >  {
> > >   struct drv_dev_and_id *ddi = _ddi;
> > >   struct device *dev = &ddi->dev->dev;
> > > + struct device *parent = dev->parent;
> > >   int rc;
> > >  
> > > + /* The parent bridge must be in active state when probing */
> > > + if (parent)
> > > +         pm_runtime_get_sync(parent);
> > 
> > Ooh, this is a very good point.  I completely missed it.
> > 
> > >   /* Unbound PCI devices are always set to disabled and suspended.
> > >    * During probe, the device is set to enabled and active and the
> > >    * usage count is incremented.  If the driver supports runtime PM,
> > > @@ -298,6 +302,8 @@ static long local_pci_probe(void *_ddi)
> > >           pm_runtime_set_suspended(dev);
> > >           pm_runtime_put_noidle(dev);
> > >   }
> > > + if (parent)
> > > +         pm_runtime_put(parent);
> > 
> > You should use pm_runtime_put_sync(), not pm_runtime_put().
> 
> Hmm, why exactly?

Because it's more efficient to do something directly than to run it in 
a workqueue.

Alan Stern

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