From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932095Ab2EJOsR (ORCPT ); Thu, 10 May 2012 10:48:17 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:57385 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755867Ab2EJOsP (ORCPT ); Thu, 10 May 2012 10:48:15 -0400 Date: Thu, 10 May 2012 10:48:14 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Huang Ying cc: "Rafael J. Wysocki" , huang ying , Bjorn Helgaas , , , , Zheng Yan , Lan Tianyu Subject: Re: [RFC v2 2/5] PM, Add sysfs file power_off to control device power off policy In-Reply-To: <1336611349.6190.245.camel@yhuang-dev> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 10 May 2012, Huang Ying wrote: > How to remove power is not general enough, but I think whether to power > off is more general. So a flag like power_must_be_on can be general and > useful. I'm not so sure about that. > > Also, from a driver's perspective the result of putting a device into > > some non-power-off low-power state may be just as unpleasant as the > > result of removing power from it. > > Yes. From device driver or bus point of view, "power off" is just like > other low power state. But from the "all devices" point of view, power > off can be the only low power state that is shared by all devices. So > we can say "power off" is special from this point of view. No -- it's not true that all devices share a "power off" state while the system is running. The only thing that can be said about all devices is that some of them can be put into one or many low-power states. That's what the PM core means when it talks about runtime suspend. Alan Stern