linux-kernel - Re: [PATCH 1/1] driver core: disable device's runtime pm during shutdown

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Date:	Tue, 6 Dec 2011 05:35:58 +1100
From:	NeilBrown <neilb@...e.de>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Ming Lei <tom.leiming@...il.com>,
	Chen Peter-B29397 <B29397@...escale.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Greg KH <greg@...ah.com>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"hzpeterchen@...il.com" <hzpeterchen@...il.com>,
	Igor Grinberg <grinberg@...pulab.co.il>
Subject: Re: [PATCH 1/1] driver core: disable device's runtime pm during
 shutdown

On Mon, 5 Dec 2011 11:02:38 -0500 (EST) Alan Stern
<stern@...land.harvard.edu> wrote:

> On Mon, 5 Dec 2011, Ming Lei wrote:
> 
> > Sorry, the above is line wrapped badly, see the below:
> > 
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index d8b3d89..96b266c 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -1743,8 +1743,9 @@ void device_shutdown(void)
> >  		 */
> >  		list_del_init(&dev->kobj.entry);
> >  		spin_unlock(&devices_kset->list_lock);
> > -		/* Disable all device's runtime power management */
> > -		pm_runtime_disable(dev);
> > +
> > +		/* put device into active state and forbit runtime pm */
> > +		pm_runtime_forbid(dev);
> > 
> >  		if (dev->bus && dev->bus->shutdown) {
> >  			dev_dbg(dev, "shutdown\n");
> 
> We don't want to put devices into the active state when it's not 
> necessary.  A better approach would be:
> 
> 		/* Don't allow any more runtime suspends */
> 		pm_runtime_get_noresume(dev);
> 		pm_runtime_barrier(dev);
> 
> Alan Stern

That sounds like a reasonable approach if we really need to do something at
this level.  But is this the only place that ->shutdown methods are called
from?  If they are called from elsewhere, would those places need the
same pm_runtime protection?

BTW I was wrong when I said that only calling pm_runtime_disable if there was
a ->shutdown function would not work for me. i.e. the following patch does
solve my particular issue (though I'm not sure it is "right").
I was getting confused by the two different devices: the i2c device and the
platform device.
The i2c device has a ->shutdown which does nothing, but doesn't need to wake
up.
The platform device is the one which needs to wake up, but it doesn't have a
->shutdown function is this patch causes it not have pm_runtime disabled.

Thanks,
NeilBrown

diff --git a/drivers/base/core.c b/drivers/base/core.c
index d8b3d89..b9aa5d2 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1743,13 +1743,13 @@ void device_shutdown(void)
 		 */
 		list_del_init(&dev->kobj.entry);
 		spin_unlock(&devices_kset->list_lock);
-		/* Disable all device's runtime power management */
-		pm_runtime_disable(dev);
 
 		if (dev->bus && dev->bus->shutdown) {
+			pm_runtime_disable(dev);
 			dev_dbg(dev, "shutdown\n");
 			dev->bus->shutdown(dev);
 		} else if (dev->driver && dev->driver->shutdown) {
+			pm_runtime_disable(dev);
 			dev_dbg(dev, "shutdown\n");
 			dev->driver->shutdown(dev);
 		}

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