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

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Date:	Thu, 11 Jun 2015 01:41:12 +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 Wednesday, June 10, 2015 12:43:15 PM Andy Shevchenko wrote:
> On Wed, 2015-06-10 at 02:08 +0200, Rafael J. Wysocki wrote:
> > 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).
> > 
> 
> Thanks for the patch! We are going to test this soon.
> 
> By the way, can you give your Ack for patches 1 and 2 if there is no
> objection?

OK


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