From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guenter Roeck Subject: Re: [PATCH v2 01/47] kernel: Add support for poweroff handler call chain Date: Tue, 21 Oct 2014 06:17:09 -0700 Message-ID: <54465CD5.5070002@roeck-us.net> References: <1413864783-3271-1-git-send-email-linux@roeck-us.net> <1413864783-3271-2-git-send-email-linux@roeck-us.net> <41603148.RJg26vx0Wv@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from bh-25.webhostbox.net ([208.91.199.152]:59287 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932510AbaJUNne (ORCPT ); Tue, 21 Oct 2014 09:43:34 -0400 Received: from mailnull by bh-25.webhostbox.net with sa-checked (Exim 4.82) (envelope-from ) id 1XgZin-001Hvh-1w for linux-pm@vger.kernel.org; Tue, 21 Oct 2014 13:43:33 +0000 In-Reply-To: <41603148.RJg26vx0Wv@vostro.rjw.lan> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Rafael J. Wysocki" Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Alan Cox , Alexander Graf , Andrew Morton , Geert Uytterhoeven , Heiko Stuebner , Lee Jones , Len Brown , Pavel Machek , =?UTF-8?B?UGhpbGlwcGUgUsOpdG9ybmF6?= , Romain Perier On 10/21/2014 05:26 AM, Rafael J. Wysocki wrote: > On Monday, October 20, 2014 09:12:17 PM Guenter Roeck wrote: >> Various drivers implement architecture and/or device specific means to >> remove power from the system. For the most part, those drivers set the >> global variable pm_power_off to point to a function within the driver. >> >> This mechanism has a number of drawbacks. Typically only one scheme >> to remove power is supported (at least if pm_power_off is used). >> At least in theory there can be multiple means remove power, some of >> which may be less desirable. For example, some mechanisms may only >> power off the CPU or the CPU card, while another may power off the >> entire system. Others may really just execute a restart sequence >> or drop into the ROM monitor. Using pm_power_off can also be racy >> if the function pointer is set from a driver built as module, as the >> driver may be in the process of being unloaded when pm_power_off is >> called. If there are multiple poweroff handlers in the system, removing >> a module with such a handler may inadvertently reset the pointer to >> pm_power_off to NULL, leaving the system with no means to remove power. >> >> Introduce a system poweroff handler call chain to solve the described >> problems. This call chain is expected to be executed from the >> architecture specific machine_power_off() function. Drivers providing >> system poweroff functionality are expected to register with this call chain. >> By using the priority field in the notifier block, callers can control >> poweroff handler execution sequence and thus ensure that the poweroff >> handler with the optimal capabilities to remove power for a given system >> is called first. > > Well, I must admit to having second thoughts regarding this particular > mechanism. Namely, notifiers don't seem to be the best way of expressing > what's needed from the design standpoint. > > It looks like we need a list of power off methods and a way to select one > of them, so it seems that using a plist would be a natural choice here? > Isn't a notifier call chain nothing but a list of methods, with its priority the means to select which one to use (first) ? The only difference I can see is that you would only select one of them, meaning the one with the highest priority, and not try the others. Am I missing something ? Thanks, Guenter