From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933409AbbFWQng (ORCPT ); Tue, 23 Jun 2015 12:43:36 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:35699 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932415AbbFWQnS (ORCPT ); Tue, 23 Jun 2015 12:43:18 -0400 Date: Tue, 23 Jun 2015 09:43:14 -0700 From: Guenter Roeck To: Fu Wei Cc: Suravee Suthikulpanit , Linaro ACPI Mailman List , linux-watchdog@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Wei Fu , G Gregory , Al Stone , Hanjun Guo , Timur Tabi , Ashwin Chaugule , Arnd Bergmann , Vipul Gandhi , Wim Van Sebroeck , Jon Masters , Leo Duran , Jon Corbet , Mark Rutland , Catalin Marinas , Will Deacon , rjw@rjwysocki.net Subject: Re: [non-pretimeout,4/7] Watchdog: introduce ARM SBSA watchdog driver Message-ID: <20150623164314.GB20017@roeck-us.net> References: <1433958452-23721-5-git-send-email-fu.wei@linaro.org> <20150611162810.GA22711@roeck-us.net> <20150623152131.GA9990@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-Authenticated_sender: guenter@roeck-us.net X-OutGoing-Spam-Status: No, score=0.0 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: authenticated_id: guenter@roeck-us.net 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 Wed, Jun 24, 2015 at 12:17:19AM +0800, Fu Wei wrote: > Hi Guenter, > > you always can provide help very quickly, thank you very much :-) > > On 23 June 2015 at 23:21, Guenter Roeck wrote: > > On Tue, Jun 23, 2015 at 09:26:35PM +0800, Fu Wei wrote: > >> Hi Guenter, > > [ ...] > > > >> > > >> >> + * When the first timeout occurs, WS0(SPI or LPI) is triggered, > >> >> + * the second timeout period(as long as the first timeout period) starts. > >> > > >> > no longer accurate if WOR is used for the second period. > >> > > >> >> + * In WS0 interrupt routine, panic() will be called for collecting > >> >> + * crashdown info. > >> >> + * If system can not recover from WS0 interrupt routine, then second > >> >> + * timeout occurs, WS1(reset or higher level interrupt) is triggered. > >> >> + * The two timeout period can be set by WOR(32bit). > >> > > >> > The second timeout period is determined by ... > >> > > >> >> + * WOR gives a maximum watch period of around 10s at the maximum > >> >> + * system counter frequency. > >> >> + * The System Counter shall run at maximum of 400MHz. > >> > > >> > "... at the maximum system counter frequency of 400 MHz.", and drop the > >> > last sentence. > >> > >> For the second timeout period, I have discussed with a kdump developers, > >> (1)10s maybe not good enough for all the case of panic + kdump, so > >> maybe we still need to use WCV in the second timeout period > >> (2)in the second timeout period, maybe we need to programme WCV for > >> two reason: a, trigger WS1 to reboot system ASAP; b, feed the watchdog > >> without cleanning WS0 flag. > >> > >> WHY we want to feed the watchdog (keepalive) without cleanning WS0 flag?? > >> REASON: > >> (1)if the system context is large, we may need to feed the dog until > >> we get all the things backed up. > >> (2)if system goes wrong, WS0 triggered, then panic--> kdump. if we > >> feed the dog by WRR or programming WOR, WS0 flag will be cleaned. Once > >> system goes wrong again, then panic again..... > >> So this system will be in a panic--kdump--panic--kdump loop, have not > >> chance to reset. > >> > >> So if we are in the second timeout period, we may need to always programme WCV. > >> > > The crashdump kernel is supposed to reload the watchdog driver, which will ping > > the watchdog. If it isn't able to do that in 10 seconds, something is wrong. > > yes, 10s maybe not enough for all case. > When I tested kdump on arm64, sometimes , it took 20s. So I am > thinking : can we make the max value of pretimeout > 10s in this > driver. > It takes more than 10 seconds to load the crashdump kernel, or it takes more than 10 seconds to complete the dump ? > > > > >> >> + > >> >> + status = readl_relaxed(gwdt->control_base + SBSA_GWDT_WCS); > >> >> + if (status & SBSA_GWDT_WCS_WS1) { > >> >> + dev_warn(dev, "System reset by WDT(WCV: %llx)\n", > >> >> + sbsa_gwdt_get_wcv(wdd)); > >> > > >> > WCV here only tells us how many clock cycles were executed since the > >> > system started (or something like that). So I still don't understand > >> > why it is valuable to print that number. > >> > >> this number provides the time of system reset, I thinks that may help > >> admin to analyse the system failure. > >> > > It doesn't mean anything to anyone but you since it is not in a well defined > > time scale. > > maybe I should convert it to second? > I think the original value is better? > I think you should drop it. Guenter