linux-kernel - Re: [PATCH 4/5 V2] usb: call pm_runtime_put_sync in pm_runtime_get

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Date:	Fri, 01 Mar 2013 01:50:30 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"Li, Fei" <fei.li@...el.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"Lan, Tianyu" <tianyu.lan@...el.com>,
	"sarah.a.sharp@...ux.intel.com" <sarah.a.sharp@...ux.intel.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5 V2] usb: call pm_runtime_put_sync in pm_runtime_get_sync failed case

On Friday, March 01, 2013 12:38:07 AM Liu, Chuansheng wrote:
> 
> > -----Original Message-----
> > From: Alan Stern [mailto:stern@...land.harvard.edu]
> > Sent: Thursday, February 28, 2013 11:17 PM
> > To: Li, Fei
> > Cc: gregkh@...uxfoundation.org; Lan, Tianyu; sarah.a.sharp@...ux.intel.com;
> > rjw@...k.pl; linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org; Liu,
> > Chuansheng
> > Subject: Re: [PATCH 4/5 V2] usb: call pm_runtime_put_sync in
> > pm_runtime_get_sync failed case
> > 
> > On Thu, 28 Feb 2013, Li Fei wrote:
> > 
> > >
> > > Even in failed case of pm_runtime_get_sync, the usage_count
> > > is incremented. In order to keep the usage_count with correct
> > > value and runtime power management to behave correctly, call
> > > pm_runtime_put(_sync) in such case.
> > >
> > > Signed-off-by Liu Chuansheng <chuansheng.liu@...el.com>
> > > Signed-off-by: Li Fei <fei.li@...el.com>
> > > ---
> > >  drivers/usb/core/hub.c |    3 ++-
> > >  1 files changed, 2 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > > index 5480352..f72dede 100644
> > > --- a/drivers/usb/core/hub.c
> > > +++ b/drivers/usb/core/hub.c
> > > @@ -3148,12 +3148,13 @@ int usb_port_resume(struct usb_device *udev,
> > pm_message_t msg)
> > >
> > >  	if (port_dev->did_runtime_put) {
> > >  		status = pm_runtime_get_sync(&port_dev->dev);
> > > -		port_dev->did_runtime_put = false;
> > >  		if (status < 0) {
> > >  			dev_dbg(&udev->dev, "can't resume usb port, status %d\n",
> > >  					status);
> > > +			pm_runtime_put_sync(&port_dev->dev);
> > >  			return status;
> > >  		}
> > > +		port_dev->did_runtime_put = false;
> > >  	}
> > 
> > I don't see much point in this.  After a failed resume, the port's
> > runtime PM status is undefined.  Whether or not you do a
> > pm_runtime_put_sync won't make any difference.
> In case of failed resume, calling pm_runtime_put_sync() is just for decrease the dev->power.usage_count,
> because pm_runtime_get_sync() always increase the dev->power.usage_count even failed.
> 
> If not pairing runtime_get/put, after that case, the device can not enter runtime suspend any more due to dev->power.usage_count > 0 always.
> Is it making sense?

Well, not really.

Before returning an error code, rpm_callback() assigns that code to
dev->power.runtime_error and that will effectively disable runtime PM for dev
going forward anyway.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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