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=ham 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 549C8C43218 for ; Mon, 10 Jun 2019 20:29:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 249E82082E for ; Mon, 10 Jun 2019 20:29:31 +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="G6f3CvIr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389337AbfFJU3a (ORCPT ); Mon, 10 Jun 2019 16:29:30 -0400 Received: from mail-pg1-f174.google.com ([209.85.215.174]:39473 "EHLO mail-pg1-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389331AbfFJU3a (ORCPT ); Mon, 10 Jun 2019 16:29:30 -0400 Received: by mail-pg1-f174.google.com with SMTP id 196so5628251pgc.6; Mon, 10 Jun 2019 13:29:30 -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=1u+Mk6P0GQp2YK+MbgZCemejiKqi+QRb5rVGWIgElFw=; b=G6f3CvIrKb/qPOpOxDrnhusVhhss4a4rdtkGIF9mDlmmqxSCz9ObWvhgBgTnml10hK JlDF0m8kSM2MRPw0DedfKg+9suAC/0w4ywoA7lTnIPx8Vd0L5QZM9kIEIdUepk9/A/Ci L3MsIhQZWfa778Ov/yadphBGN+mqRGE4K8TJ0XcXmyKaYfOK0bHJNtcQJNQTlOX6mgPf 64bOa+0uK/5ghOUmBiBDDHn00kAT8AOzLX3YDmwNBbldXKVw7I5mp39nlvqkgaTnQFLn YHKUn9nd/mzA8vWJXcCk0LQFfz3S9tv6sz66Jd4qeWovTDBwzjn2zTC5wxejL248uT+B It3A== 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=1u+Mk6P0GQp2YK+MbgZCemejiKqi+QRb5rVGWIgElFw=; b=n1MH7YF2AMUJYxCjcTAitWgMS/TyxrkYjX2PFIibfmSDv6CapqXHy+5s8/ehvn11c2 2u5GYBgskzqzguJxVrtUm03nMqaXEcuY4eptEgQb3RNBpGdJeIFcXy8BYKqoRmxm/IuI lLPKrg237ExH9LQC4Z/FyEMB7VRd7qun/HmR+Lq3+pvPFRYoZK6nH64KXsoSracgLlD8 MlNrEGvY3IxgxPDaKtHJBy6Jb8AAk1HxOZXjcVbAwmHRCMs+QDwjCAymOeGv2hFp3o7/ YWWm2NdqbnhCJ8xGOXQTjw2Szm3ZN7W5ct5+/zVBOHuCjNFtUQ5bXkgpHgUOrMKcotvZ xFiw== X-Gm-Message-State: APjAAAUJ4W4jkWAKB8AHaIPnA1JuGTRIcBiPo7yq1jSEXhRsbZskxoiL EzFGklwhnxBSy/uwbWSYdLg= X-Google-Smtp-Source: APXvYqz8RUYRoaZm+zRUDtcye0JXQIhd3kp2snzDV/NHDjl0J3yKwIxNh87p7iEdeOMp2hurxqjFtA== X-Received: by 2002:a62:5801:: with SMTP id m1mr77055067pfb.32.1560198569901; Mon, 10 Jun 2019 13:29:29 -0700 (PDT) Received: from localhost ([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id 131sm6435257pfx.57.2019.06.10.13.29.28 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Jun 2019 13:29:29 -0700 (PDT) Date: Mon, 10 Jun 2019 13:29:28 -0700 From: Guenter Roeck To: Alexandre Belloni Cc: Ken Sloat , "Nicolas.Ferre@microchip.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: <20190610202928.GB13191@roeck-us.net> References: <20190610162811.GA11270@roeck-us.net> <20190610201301.GH25472@piout.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190610201301.GH25472@piout.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-watchdog-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-watchdog@vger.kernel.org On Mon, Jun 10, 2019 at 10:13:01PM +0200, Alexandre Belloni wrote: > Hello, > > On 10/06/2019 09:28:11-0700, Guenter Roeck wrote: > > 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 ? > > > > There are customers that protects suspend/resume using the watchdog. > They wake up their platform every 15s to ping the watchdog. > Interesting use case. > Also, I don't see why the application deciding to go to suspend wouldn't > be able to disable the watchdog before do so if this is the wanted policy. > Many watchdog drivers already implement suspend/resume support. Such a platform specific functionality seems to be quite undesirable to me. Besides (and pretty much all watchdog drivers implementing suspend/resume do that wrong), you'd likely want to disable the watchog late during suspend and early during resume to reduce the risk of a hang. I don't think you can do that from userspace. Thanks, Guenter