linux-kernel - Re: [PATCH v3 3/8] Driver core: wakeup the parent device before trying probe

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Date:	Wed, 10 Jun 2015 02:08:54 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Lee Jones <lee.jones@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	Mike Turquette <mturquette@...aro.org>
Subject: Re: [PATCH v3 3/8] Driver core: wakeup the parent device before trying probe

On Tuesday, June 09, 2015 01:42:00 AM Rafael J. Wysocki wrote:
> On Monday, June 01, 2015 05:47:57 PM Andy Shevchenko wrote:
> > From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > 
> > If the parent is still suspended when driver probe is
> > attempted, the result may be failure.
> > 
> > For example, if the parent is a PCI MFD device that has been
> > suspended when we try to probe our device, any register
> > reads will return 0xffffffff.
> > 
> > To fix the problem, making sure the parent is always awake
> > before attempting driver probe.
> > 
> > Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > ---
> >  drivers/base/dd.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> > index e843fdb..cfbeff3 100644
> > --- a/drivers/base/dd.c
> > +++ b/drivers/base/dd.c
> > @@ -399,6 +399,8 @@ EXPORT_SYMBOL_GPL(wait_for_device_probe);
> >   *
> >   * This function must be called with @dev lock held.  When called for a
> >   * USB interface, @dev->parent lock must be held as well.
> > + *
> > + * If device has a parent it will be powered on during device's probe().
> >   */
> >  int driver_probe_device(struct device_driver *drv, struct device *dev)
> >  {
> > @@ -410,10 +412,16 @@ int driver_probe_device(struct device_driver *drv, struct device *dev)
> >  	pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
> >  		 drv->bus->name, __func__, dev_name(dev), drv->name);
> >  
> > +	if (dev->parent)
> > +		pm_runtime_get_sync(dev->parent);
> > +
> 
> For some bus types that will resume and suspend the parent for many times in
> a row in device_attach() until an appropriate driver is found.  Would it be
> more efficient to call it once before the bus_for_each_drv() loop in there?

Actually, something like the below should work too (the bumping up of the
parent's usage counter before the loop will keep it in the runtime-active
state throughout the loop).

---
 drivers/base/dd.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

Index: linux-pm/drivers/base/dd.c
===================================================================
--- linux-pm.orig/drivers/base/dd.c
+++ linux-pm/drivers/base/dd.c
@@ -399,6 +399,8 @@ EXPORT_SYMBOL_GPL(wait_for_device_probe)
  *
  * This function must be called with @dev lock held.  When called for a
  * USB interface, @dev->parent lock must be held as well.
+ *
+ * If the device has a parent, runtime-resume the parent before driver probing.
  */
 int driver_probe_device(struct device_driver *drv, struct device *dev)
 {
@@ -410,10 +412,16 @@ int driver_probe_device(struct device_dr
 	pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
 		 drv->bus->name, __func__, dev_name(dev), drv->name);
 
+	if (dev->parent)
+		pm_runtime_get_sync(dev->parent);
+
 	pm_runtime_barrier(dev);
 	ret = really_probe(dev, drv);
 	pm_request_idle(dev);
 
+	if (dev->parent)
+		pm_runtime_put(dev->parent);
+
 	return ret;
 }
 
@@ -459,8 +467,14 @@ int device_attach(struct device *dev)
 			ret = 0;
 		}
 	} else {
+		if (dev->parent)
+			pm_runtime_get_sync(dev->parent);
+
 		ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
 		pm_request_idle(dev);
+
+		if (dev->parent)
+			pm_runtime_put(dev->parent);
 	}
 out_unlock:
 	device_unlock(dev);

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