linux-kernel - Re: [PATCH 1/6] PM: Introduce PM links framework

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Message-Id: <200908282111.19925.rjw@sisk.pl>
Date:	Fri, 28 Aug 2009 21:11:19 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"linux-pm" <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>,
	Pavel Machek <pavel@....cz>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 1/6] PM: Introduce PM links framework

On Friday 28 August 2009, Alan Stern wrote:
> On Wed, 26 Aug 2009, Rafael J. Wysocki wrote:
> 
> > From: Rafael J. Wysocki <rjw@...k.pl>
> > 
> > Introduce a framework for representing off-tree PM dependencies
> > between devices.
> > 
> > There are PM dependencies between devices that are not reflected by
> > the structure of the device tree.  In other words, as far as PM is
> > concerned, a device may depend on some other devices which are not
> > its children and none of which is its parent.
> > 
> > Every such dependency involves two devices, one of which is a
> > "master" and the other of which is a "slave", meaning that the
> > "slave" have to be suspended before the "master" and cannot be
> > woken up before it.  Thus every device can be given two lists of
> > "dependency objects", one for the dependencies where the device is
> > the "master" and the other for the dependencies where the device is
> > the "slave".  Then, each "dependency object" can be represented as
> 
> 
> > Index: linux-2.6/drivers/base/power/common.c
> > ===================================================================
> > --- /dev/null
> > +++ linux-2.6/drivers/base/power/common.c
> 
> > +/**
> > + * device_for_each_master - Execute given function for each master of a device.
> > + * @slave: Device whose masters to execute the function for.
> > + * @data: Data pointer to pass to the function.
> > + * @fn: Function to execute for each master of @slave.
> > + *
> > + * The function is executed for the parent of the device, if there is one, and
> > + * for each device connected to it via a pm_link object where @slave is the
> > + * "slave".
> > + */
> > +int device_for_each_master(struct device *slave, void *data,
> > +			   int (*fn)(struct device *dev, void *data))
> > +{
> > +	struct pm_link *link;
> > +	int idx;
> > +	int error = 0;
> > +
> > +	if (slave->parent) {
> > +		error = fn(slave->parent, data);
> > +		if (error)
> > +			return error;
> > +	}
> > +
> > +	idx = srcu_read_lock(&pm_link_ss);
> > +
> > +	list_for_each_entry(link, &slave->power.slave_links, slave_hook) {
> 
> This needs to use list_for_each_entry_rcu.  Likewise in
> device_for_each_slave().

OK, I wasn't sure about that.

Thanks,
Rafael
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