Message-ID: <1352337308.7176.28.camel@yhuang-dev>
Subject: Re: [BUGFIX] PM: Fix active child counting when disabled and
 forbidden
From: Huang Ying <ying.huang@intel.com>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Alan Stern <stern@rowland.harvard.edu>, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org
Date: Thu, 08 Nov 2012 09:15:08 +0800
In-Reply-To: <38669905.umVnjWsO2W@vostro.rjw.lan>
References: <Pine.LNX.4.44L0.1211071653140.1188-100000@iolanthe.rowland.org>
	 <1748065.Php9fUYGsh@vostro.rjw.lan> <38669905.umVnjWsO2W@vostro.rjw.lan>
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On Thu, 2012-11-08 at 00:09 +0100, Rafael J. Wysocki wrote:
> On Wednesday, November 07, 2012 11:51:15 PM Rafael J. Wysocki wrote:
> > On Wednesday, November 07, 2012 04:56:49 PM Alan Stern wrote:
> > > On Wed, 7 Nov 2012, Rafael J. Wysocki wrote:
> > > 
> > > > > Right.  The reasoning behind my proposal goes like this: When there's
> > > > > no driver, the subsystem can let userspace directly control the
> > > > > device's power level through the power/control attribute.
> > > > 
> > > > Well, we might as well just leave the runtime PM of PCI devices enabled, even
> > > > if they have no drivers, but modify the PCI bus type's runtime PM callbacks
> > > > to ignore devices with no drivers.
> > > > 
> > > > IIRC the reason why we decided to disable runtime PM for PCI device with no
> > > > drivers was that some of them refused to work again after being put by the
> > > > core into D3.  By making the PCI bus type's runtime PM callbacks ignore them
> > > > we'd avoid this problem without modifying the core's behavior.
> > > 
> > > It comes down to a question of the parent.  If a driverless PCI device
> > > isn't being used, shouldn't its parent be allowed to go into runtime
> > > suspend?  As things stand now, we do allow it.
> > > 
> > > The problem is that we don't disallow it when the driverless device
> > > _is_ being used.
> > 
> > We can make it depend on what's there in the control file.  Let's say if that's
> > "on" (ie. the devices usage counter is not zero), we won't allow the parent
> > to be suspended.
> > 
> > So, as I said, why don't we keep the runtime PM of PCI devices always enabled,
> > regardless of whether or not there is a driver, and arrange things in such a
> > way that the device is automatically "suspended" if user space writes "auto"
> > to the control file.  IOW, I suppose we can do something like this:
> 
> It probably is better to treat the "no driver" case in a special way, though:
> 
> ---
>  drivers/pci/pci-driver.c |   45 +++++++++++++++++++++++++--------------------
>  drivers/pci/pci.c        |    2 ++
>  2 files changed, 27 insertions(+), 20 deletions(-)
> 
> Index: linux-pm/drivers/pci/pci-driver.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci-driver.c
> +++ linux-pm/drivers/pci/pci-driver.c
> @@ -263,22 +263,17 @@ static long local_pci_probe(void *_ddi)
>  	/* The parent bridge must be in active state when probing */
>  	if (parent)
>  		pm_runtime_get_sync(parent);
> -	/* 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,
> -	 * it should call pm_runtime_put_noidle() in its probe routine and
> +	/*
> +	 * During probe, the device is set to active and the usage count is
> +	 * incremented.  If the driver supports runtime PM, it should call
> +	 * pm_runtime_put_noidle() in its probe routine and
>  	 * pm_runtime_get_noresume() in its remove routine.
>  	 */
> -	pm_runtime_get_noresume(dev);
> -	pm_runtime_set_active(dev);
> -	pm_runtime_enable(dev);
> -
> +	pm_runtime_get_sync(dev);
>  	rc = ddi->drv->probe(ddi->dev, ddi->id);
> -	if (rc) {
> -		pm_runtime_disable(dev);
> -		pm_runtime_set_suspended(dev);
> -		pm_runtime_put_noidle(dev);
> -	}
> +	if (rc)
> +		pm_runtime_put_sync(dev);
> +
>  	if (parent)
>  		pm_runtime_put(parent);
>  	return rc;
> @@ -369,9 +364,7 @@ static int pci_device_remove(struct devi
>  	}
>  
>  	/* Undo the runtime PM settings in local_pci_probe() */
> -	pm_runtime_disable(dev);
> -	pm_runtime_set_suspended(dev);
> -	pm_runtime_put_noidle(dev);
> +	pm_runtime_put_sync(dev);
>  
>  	/*
>  	 * If the device is still on, set the power state as "unknown",
> @@ -998,10 +991,14 @@ static int pci_pm_restore(struct device
>  static int pci_pm_runtime_suspend(struct device *dev)
>  {
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
> -	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
> +	const struct dev_pm_ops *pm;
>  	pci_power_t prev = pci_dev->current_state;
>  	int error;
>  
> +	if (!dev->driver)
> +		return 0;
> +
> +	pm = dev->driver->pm;
>  	if (!pm || !pm->runtime_suspend)
>  		return -ENOSYS;
>  
> @@ -1035,8 +1032,12 @@ static int pci_pm_runtime_resume(struct
>  {
>  	int rc;
>  	struct pci_dev *pci_dev = to_pci_dev(dev);
> -	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
> +	const struct dev_pm_ops *pm;
> +
> +	if (!dev->driver)
> +		return 0;
>  
> +	pm = dev->driver->pm;
>  	if (!pm || !pm->runtime_resume)
>  		return -ENOSYS;
>  
> @@ -1054,8 +1055,12 @@ static int pci_pm_runtime_resume(struct
>  
>  static int pci_pm_runtime_idle(struct device *dev)
>  {
> -	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
> +	const struct dev_pm_ops *pm;
> +
> +	if (!dev->driver)
> +		goto out:
>  
> +	pm = dev->driver->pm;
>  	if (!pm)
>  		return -ENOSYS;
>  
> @@ -1065,8 +1070,8 @@ static int pci_pm_runtime_idle(struct de
>  			return ret;
>  	}
>  
> + out:
>  	pm_runtime_suspend(dev);
> -
>  	return 0;
>  }
>  
> Index: linux-pm/drivers/pci/pci.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/pci.c
> +++ linux-pm/drivers/pci/pci.c
> @@ -1868,6 +1868,8 @@ void pci_pm_init(struct pci_dev *dev)
>  	u16 pmc;
>  
>  	pm_runtime_forbid(&dev->dev);
> +	pm_runtime_set_active(dev);
> +	pm_runtime_enable(&dev->dev);
>  	device_enable_async_suspend(&dev->dev);
>  	dev->wakeup_prepared = false;
>  

I think the patch can fix the issue in a better way.

Do we still need to clarify state about disabled and forbidden?  When a
device is forbidden and the usage_count > 0, is it a good idea to allow
to set device state to SUSPENDED if the device is disabled?

Best Regards,
Huang Ying


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