From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753872AbaG3O2f (ORCPT ); Wed, 30 Jul 2014 10:28:35 -0400 Received: from mail.active-venture.com ([67.228.131.205]:58609 "EHLO mail.active-venture.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753334AbaG3O2c (ORCPT ); Wed, 30 Jul 2014 10:28:32 -0400 X-Originating-IP: 108.223.40.66 Message-ID: <53D9010B.7070700@roeck-us.net> Date: Wed, 30 Jul 2014 07:28:27 -0700 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 MIME-Version: 1.0 To: =?windows-1252?Q?Heiko_St=FCbner?= CC: linux-watchdog@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Wim Van Sebroeck , Catalin Marinas , Maxime Ripard , Will Deacon , Arnd Bergmann , Russell King , Jonas Jensen , Randy Dunlap , Andrew Morton , Steven Rostedt , Ingo Molnar , Dmitry Eremin-Solenikov , David Woodhouse , Tomasz Figa , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 0/7] kernel: Add support for restart handler call chain References: <1405668856-13738-1-git-send-email-linux@roeck-us.net> <53D84F77.2050401@roeck-us.net> <1705554.pBhZQ0Icu9@diego> <53D8FCEA.9020506@roeck-us.net> In-Reply-To: <53D8FCEA.9020506@roeck-us.net> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/30/2014 07:10 AM, Guenter Roeck wrote: > On 07/30/2014 05:16 AM, Heiko Stübner wrote: >> Hi Guenter, >> >> Am Dienstag, 29. Juli 2014, 18:50:47 schrieb Guenter Roeck: >>> On 07/18/2014 12:34 AM, Guenter Roeck wrote: >>>> Various drivers implement architecture and/or device specific means >>>> to restart (reset) the system. Various mechanisms have been implemented >>>> to support those schemes. The best known mechanism is arm_pm_restart, >>>> which is a function pointer to be set either from platform specific code >>>> or from drivers. Another mechanism is to use hardware watchdogs to issue >>>> a reset; this mechanism is used if there is no other method available >>>> to reset a board or system. Two examples are alim7101_wdt, which currently >>>> uses the reboot notifier to trigger a reset, and moxart_wdt, which >>>> registers the arm_pm_restart function. Several other restart drivers for >>>> arm, all directly calling arm_pm_restart, are in the process of being >>>> integrated into the kernel. All those drivers would benefit from the new >>>> API. >>>> >>>> The existing mechanisms have a number of drawbacks. Typically only one >>>> scheme to restart the system is supported (at least if arm_pm_restart is >>>> used). At least in theory there can be multiple means to restart the >>>> system, some of which may be less desirable (for example one mechanism >>>> may only reset the CPU, while another may reset the entire system). Using >>>> arm_pm_restart can also be racy if the function pointer is set from a >>>> driver, as the driver may be in the process of being unloaded when >>>> arm_pm_restart is called. >>>> Using the reboot notifier is always racy, as it is unknown if and when >>>> other functions using the reboot notifier have completed execution >>>> by the time the watchdog fires. >>>> >>>> Introduce a system restart handler call chain to solve the described >>>> problems. This call chain is expected to be executed from the >>>> architecture specific machine_restart() function. Drivers providing >>>> system restart functionality (such as the watchdog drivers mentioned >>>> above) are expected to register with this call chain. By using the >>>> priority field in the notifier block, callers can control restart handler >>>> execution sequence and thus ensure that the restart handler with the >>>> optimal restart capabilities for a given system is called first. >>>> >>>> Since the first revision of this patchset, a number of separate patch >>>> submissions have been made which either depend on it or could make use of >>>> it. >>>> >>>> http://www.spinics.net/linux/lists/arm-kernel/msg344796.html >>>> >>>> registers three notifiers. >>>> >>>> https://lkml.org/lkml/2014/7/8/962 >>>> >>>> would benefit from it. >>>> >>>> Patch 1 of this series implements the restart handler function. Patches 2 >>>> and 3 implement calling the restart handler chain from arm and arm64 >>>> restart code. >>>> >>>> Patch 4 modifies the restart-poweroff driver to no longer call >>>> arm_pm_restart directly but machine_restart. This is done to avoid >>>> calling arm_pm_restart from more than one place. The change makes the >>>> driver architecture independent, so it would be possible to drop the arm >>>> dependency from its Kconfig entry. >>>> >>>> Patch 5 and 6 convert existing restart handlers in the watchdog subsystem >>>> to use the restart handler. Patch 7 unexports arm_pm_restart to ensure >>>> that no one gets the idea to implement a restart handler as module. >>>> >>>> --- >>>> v5: Rebased series to v3.16-rc5 >>>> >>>> Function renames: >>>> register_restart_notifier -> register_restart_handler >>>> unregister_restart_notifier -> unregister_restart_handler >>>> kernel_restart_notify -> do_kernel_restart >>>> >>>> v4: Document restart notifier priorities >>>> >>>> Select 128 as default priority for newly introduced notifiers >>>> Fix checkpatch warning (line too long) in moxart patch >>>> >>>> v3: Drop RFC. >>>> >>>> Add kernel_restart_notify wrapper function to execute notifier >>>> Improve documentation. >>>> Move restart_notifier_list into kernel/reboot.c and make it static. >>>> >>>> v2: Add patch 4. >>>> >>>> Only call blocking notifier call chain if arm_pm_restart was not set. >>>> >>>> -- >>> >>> To get more test coverage, this series plus a few add-on patches which >>> depend on it are now available in the restart-staging branch of my >>> repository at kernel.org [1]. The branch is currently based on 3.16-rc7. >>> Extensive build test results are available at [2]; look for the column >>> marked 'restart-staging' on the far right of the tables. >>> >>> I would encourage everyone interested in this series to send me Reviewed-by: >>> or at least Acked-by: tags. Note that I removed all of the earlier tags >>> since I feel that the changes made subsequently warrant updated tags. An >>> Acked-by: from affected maintainers would also be very helpful. >> >> Thanks for adapting my Samsung restart-patches to the API changes. >> >> The one thing I found is, in >> "clk: samsung: register restart handlers for s3c2412 and s3c2443" >> you seem to have forgotten the priority in the clk-s3c2443.c part while in >> clk-s3c2412.c it is present. >> > Yes, you are correct. I fixed that after I got the message from Fengguang's > robot. Which means that my auto-builder misses to build that file. Too bad > that arm:allmodconfig fails with other errors and is unusable. Do you know > if there is a defconfig which builds clk-s3c2443.c ? > >> And I'm not sure if there shouldn't be some sort of delay, to give the >> watchdog some time to work, as Tomasz suggested in my initial submission? >> > In your case the reset handler is in the clock code, itn's it ? Question > would be if the write to SWRST results in an immediate reset or if it needs > a delay. From the context, it looks to me as if reaction would be immediate, > but obviously I don't have the specification so that is just a wild guess. > After re-reading your patches, I guess you refer to the s3c2410 changes. Yes, that could use a delay. Care to send an updated patch ? Thanks, Guenter