Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932805AbaJUNng (ORCPT ); Tue, 21 Oct 2014 09:43:36 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:59291 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932685AbaJUNne (ORCPT ); Tue, 21 Oct 2014 09:43:34 -0400 Message-ID: <54465CD5.5070002@roeck-us.net> Date: Tue, 21 Oct 2014 06:17:09 -0700 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 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 Subject: Re: [PATCH v2 01/47] kernel: Add support for poweroff handler call chain 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> In-Reply-To: <41603148.RJg26vx0Wv@vostro.rjw.lan> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-CTCH-PVer: 0000001 X-CTCH-Spam: Unknown X-CTCH-VOD: Unknown X-CTCH-Flags: 0 X-CTCH-RefID: str=0001.0A020208.54466306.02DF,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0 X-CTCH-Score: 0.000 X-CTCH-ScoreCust: 0.000 X-CTCH-Rules: C_4847, X-CTCH-SenderID: linux@roeck-us.net X-CTCH-SenderID-Flags: 0 X-CTCH-SenderID-TotalMessages: 8 X-CTCH-SenderID-TotalSpam: 0 X-CTCH-SenderID-TotalSuspected: 0 X-CTCH-SenderID-TotalConfirmed: 0 X-CTCH-SenderID-TotalBulk: 0 X-CTCH-SenderID-TotalVirus: 0 X-CTCH-SenderID-TotalRecipients: 0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: mailgid no entry from get_relayhosts_entry X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 -- 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/