From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 40376C31E40 for ; Mon, 10 Jun 2019 16:28:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 18C2020859 for ; Mon, 10 Jun 2019 16:28:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="kXJKW/rT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727549AbfFJQ2Q (ORCPT ); Mon, 10 Jun 2019 12:28:16 -0400 Received: from mail-pf1-f174.google.com ([209.85.210.174]:35183 "EHLO mail-pf1-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725270AbfFJQ2P (ORCPT ); Mon, 10 Jun 2019 12:28:15 -0400 Received: by mail-pf1-f174.google.com with SMTP id d126so5614409pfd.2; Mon, 10 Jun 2019 09:28:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=pzj2b7hhZ6YD/6WjtCfGTasSPRqjwrp/TQaWna9lfxQ=; b=kXJKW/rTaV349rH2wd2kV6vNyJDRVZDsMUieB0amtC3z2MOtjzZbgDTCBZh5U5eSGS UxkGP6xS31s2n9lrkS+hvcUCsyD6X8O+nYZSPIWF+A6d/moRShUOf73RMiZsQNi3uq6Y bQtvKasAaLHPNTtI7oL1owlaJhtixBq1H3FOnMIye7VZDHUmKpBLD/IP7kvb8c9/yN7c sut9J6cyeFklUe+8T0UqEpTVVkFyOC+XTxdq+j6asKfP4bJwAWsJnLDQIuDEy3MO31T0 ljyr4/C0QWt3Xe/J9v8peYKk2fSABVUaoMa2hTtvTRrQbO9tk3SUFEVLadOQgbFn1e7O fnAg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=pzj2b7hhZ6YD/6WjtCfGTasSPRqjwrp/TQaWna9lfxQ=; b=j550qcdFbMDxToU2Scem/MZzc8QP1LNhlmvZawdlLgetCieWZgmjg68niz4P9a8ZIe aGYQaG/xyPAFLapTeMWK66m3LJfTMQUfoBOoNL7Usg/b/v/HyNn1AExRwQAxDbe7ljtp KwIfhXWpJLifeDI5LQiLFI8b9kNVNxt0csMbZYknAF+km8Z5IhctjMA1VGLswGzrDcuh 8GVsPPdPvMHZrEgmyo40n3xuIyPALDOMzRGQjPJhgsLn8RhqRBCE2Zcr7d7qw/UEA8Nu ik79VY877bNNCg9giwP/AyIxyfy9gGcsgq6uiUP+bHykLOwDm1IOaarTf3zesE7iMLqT 41dw== X-Gm-Message-State: APjAAAWDPtghtkvm/nrrQ1FFpdiYhTHuY6NxOm924uL7IMqI20EVol28 M2iPtPkPd77uhbZ5FvMaH0g= X-Google-Smtp-Source: APXvYqzTViCOZCWdvHqZEgftq3IgTD0jneFi/Mem0y2YPV1OcS6ucnGC/wdKzKKtq7K2fg6dqre64A== X-Received: by 2002:a63:5207:: with SMTP id g7mr15864200pgb.356.1560184094523; Mon, 10 Jun 2019 09:28:14 -0700 (PDT) Received: from localhost ([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id m24sm13643054pgh.75.2019.06.10.09.28.12 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Jun 2019 09:28:13 -0700 (PDT) Date: Mon, 10 Jun 2019 09:28:11 -0700 From: Guenter Roeck To: Ken Sloat Cc: "Nicolas.Ferre@microchip.com" , "alexandre.belloni@free-electrons.com" , "wim@iguana.be" , "linux-arm-kernel@lists.infradead.org" , "linux-watchdog@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [RFE]: watchdog: atmel: atmel-sama5d4-wdt Message-ID: <20190610162811.GA11270@roeck-us.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 10, 2019 at 03:51:52PM +0000, Ken Sloat wrote: > Hello Nicolas, > > I wanted to open a discussion proposing new functionality to allow disabling of the watchdog timer upon entering > suspend in the SAMA5D2/4. > > Typical use case of a hardware watchdog timer in the kernel is a userspace application opens the watchdog timer and > periodically "kicks" it. If the application hits a deadlock somewhere and is no longer able to kick it, then the watchdog > intervenes and often resets the processor. Such is the case for the Atmel driver (which also allows a watchdog interrupt > to be asserted in lieu of a system reset). In most use cases, upon entering a low power/suspend state, the application > will no longer be able to "kick" the watchdog. If the watchdog is not disabled or kicked via another method, then it will > reset the system. This is the current behavior of the Atmel driver as of today. > > The watchdog peripheral itself does have a "WDIDLEHLT" bit however, and this is enabled via the "atmel,idle-halt" dt > property. However, this is not very useful, as it literally only makes the watchdog count when the CPU is active. This > results in non-deterministic triggering of the WDT and means that if a critical application were to crash, it may be > quite a long time before the WDT would ever trigger. Below is a similar statement made in the device-tree doc for this > peripheral: > > - atmel,idle-halt: present if you want to stop the watchdog when the CPU is > in idle state. > CAUTION: This property should be used with care, it actually makes the > watchdog not counting when the CPU is in idle state, therefore the > watchdog reset time depends on mean CPU usage and will not reset at all > if the CPU stop working while it is in idle state, which is probably > not what you want. > > It seems to me, that it would be logical and useful to introduce a new property that would cause the Atmel WDT > to disable on suspend and re-enable on resume. It also appears that the WDT is re-initialized anyways upon > resume, so the only piece missing here would really be a dt flag and a call to disable. > Wondering - why would this need a dt property ? That would be quite unusual. Is there a condition where one would _not_ want the watchdog to stop on suspend ? If anything I would suggest to drop atmel,idle-halt completely; it really looks like it would make the watchdog unreliable. Thanks, Guenter