linux-kernel - Re: [RFC][Update 2][PATCH 2/4] ACPI / PM: Expose reference count values of ACPI power resources

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Date:	Mon, 21 Jan 2013 12:53:57 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Kristen C. Accardi" <kristen.c.accardi@...el.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFC][Update 2][PATCH 2/4] ACPI / PM: Expose reference count
 values of ACPI power resources

On Mon, Jan 21, 2013 at 02:05:47PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Since ACPI power resources are going to be used more extensively on
> new hardware platforms, it becomes necessary for user space (powertop
> in particular) to observe some properties of those resources for
> diagnostics purposes.
> 
> For this reason, export the reference counts of ACPI power resources
> to user space by adding a new reference_count attribute to the sysfs
> directory representing each power resource.  The value read from
> that attribute represents the number of devices using the power
> resource at the given time.  If that value is 0, it meas that the
> power resource is not used and therefore it has been turned off.

Why does userspace need to know a reference count?  Is it so that if it
is not 0, it can work to try to lower it to 0?  Or something else?

thanks,

greg k-h
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