linux-kernel - Re: [PATCH v3 2/2] PM / Runtime: Add pm_runtime_enable

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Message-ID: <Pine.LNX.4.44L0.1505191345480.1453-100000@iolanthe.rowland.org>
Date:	Tue, 19 May 2015 13:49:15 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
cc:	linux-pm@...r.kernel.org,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Kevin Hilman <khilman@...aro.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] PM / Runtime: Add pm_runtime_enable_recursive

On Tue, 19 May 2015, Tomeu Vizoso wrote:

> This function makes less cumbersome to enable runtime PM in a device and
> its descendants.
> 
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>

I don't see the point of this.  In the scenario you have in mind, are
the device and all its descendants registered by the same
subsystem/driver?  If they are, can't the subsystem/driver code enable
runtime PM for each of them when they are registered, by adding a
single call in the right spot?

If they don't all belong to the same subsystem/driver, who is going to 
call your pm_runtime_enable_recursive routine?  No single caller will 
have the right to enable runtime PM for all these devices.

Alan Stern

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