Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759502Ab1FWOUC (ORCPT ); Thu, 23 Jun 2011 10:20:02 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:43220 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1758901Ab1FWOT7 (ORCPT ); Thu, 23 Jun 2011 10:19:59 -0400 Date: Thu, 23 Jun 2011 10:19:59 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: "Rafael J. Wysocki" cc: Kevin Hilman , Linux PM mailing list , Greg Kroah-Hartman , Magnus Damm , Paul Walmsley , LKML , Subject: Re: [Update][PATCH 7/8] PM / Domains: System-wide transitions support for generic domains (v3) In-Reply-To: <201106230016.46704.rjw@sisk.pl> 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 Content-Length: 1928 Lines: 39 On Thu, 23 Jun 2011, Rafael J. Wysocki wrote: > Well, let's say this part of the documentation is slightly outdated. > > It basically refers to the model in which system suspend is a separate global > hardware or firmware operation, so the state of devices may be changed by the > BIOS or whatever takes over control in the meantime. In that case the kernel > has to ensure that the states of devices are consistent with what it thinks > about them and the simplest way to achieve that is to put the devices to > full power during resume (and back to low power if that's desirable). > > However, in the case of the systems this patchset is intended for system > suspend is achieved by putting various hardware components into low-power > states directly in a coordinated way and the system sleep state effectively > follows from the low-power states the hardware components end up in. The > system is woken up from this state by an interrupt or another mechanism under > the kernel's control. As a result, the kernel never gives control away, so > the state of devices after the resume is precisely known to it. > In consequence, it need not ensure that the state of devices is consistent with > its view, because it knows that this is the case. :-) That's true for system suspend, but it's probably not true for hibernation, even in embedded systems. Of course, many embedded systems don't use hibernation at all -- but those that do should be aware of this issue. > So the documentation should be updated to say what hardware model it is > referring to. It might be worthwhile to include a little warning about the difference between suspend and hibernate. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/