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

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Message-ID: <Pine.LNX.4.44L0.1112051544350.5138-100000@iolanthe.rowland.org>
Date:	Mon, 5 Dec 2011 15:55:09 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	NeilBrown <neilb@...e.de>
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 Tue, 6 Dec 2011, NeilBrown wrote:

> > 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?

I don't know if shutdown methods are called from anywhere else, but 
they shouldn't be.  The kerneldoc for struct bus_type plainly says:

* @shutdown:	Called at shut-down time to quiesce the device.

> 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);
>  		}

Still, it's quite conceivable that a shutdown routine might want to 
resume a device that had been runtime-suspended.  Disabling runtime PM 
for that device would prevent the routine from doing its work.

The original problem the $SUBJECT patch was meant to solve was that a
runtime-PM suspend method was called after the shutdown routine had
run.  Doing a runtime_pm_get_noresume() ought to solve this.

There still remains the possibility of a runtime resume method being
called after the shutdown routine.  So far nobody has complained about
that happening except you -- and your complaint was that it didn't
work, not that it shouldn't happen.  But if necessary, individual
drivers could add pm_runtime_disable() calls to their shutdown
routines.

Alan Stern

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