From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755447AbcEFASq (ORCPT ); Thu, 5 May 2016 20:18:46 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:52215 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752471AbcEFASo (ORCPT ); Thu, 5 May 2016 20:18:44 -0400 Subject: Re: [PATCH RFC] Watchdog: sbsa_gwdt: Enhance timeout range To: Timur Tabi , Pratyush Anand References: <5728A7C3.4010001@roeck-us.net> <20160503143856.GE13045@dhcppc6.redhat.com> <5728BEC4.6050603@codeaurora.org> <20160503155141.GF13045@dhcppc6.redhat.com> <20160503171602.GA2518@roeck-us.net> <20160504141449.GG13045@dhcppc6.redhat.com> <572A0577.1070000@codeaurora.org> <20160504155932.GH13045@dhcppc6.redhat.com> <572A2099.4070901@codeaurora.org> <20160505164300.GA16914@roeck-us.net> <20160505182031.GB12434@dhcppc6.redhat.com> <572B8F52.2000709@codeaurora.org> <572BD8E3.4070707@roeck-us.net> <572BD959.3090507@codeaurora.org> <572BDB30.9060602@codeaurora.org> Cc: fu.wei@linaro.org, Suravee.Suthikulpanit@amd.com, wim@iguana.be, linux-arm-kernel@lists.infradead.org, linux-watchdog@vger.kernel.org, open list , Dave Young , kexec@lists.infradead.org From: Guenter Roeck Message-ID: <572BE2CC.4020606@roeck-us.net> Date: Thu, 5 May 2016 17:18:20 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <572BDB30.9060602@codeaurora.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 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: linux@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: linux@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 05/05/2016 04:45 PM, Timur Tabi wrote: > Timur Tabi wrote: >> >>> A 32-bit counter is absolutely fine. Letting it run with a 400MHz clock >>> (or was it 200 MHz ?) is the problem. A resolution of 2.5ns for a >>> watchdog >>> timer does not really make any sense. >> >> The 10 second limit is based on a 20MHz clock. > > No, that's not true. I misread the code. I knew something was wrong, but it didn't click until just now. > > The default timeout is 10 seconds. The max timeout on a 20MHz system (which is what we're running) is over 200 seconds. > > The problem is that Pratyush's system is running at a clock that's way too fast: > > [ 131.187562] sbsa-gwdt sbsa-gwdt.0: Initialized with 40s timeout @ 250000000 Hz, action=1. > > 250MHz is unreasonable. Pratyush, why is your system counter so high? On our ARM64 system, it's set to 20MHz. > Guess that answers my earlier question. Problem is that the specification _permits_ those unreasonable frequencies, and quite obviously they are being used, no matter if it makes sense or not. With a (still unreasonable) maximum frequency of 100 MHz, the problem would not exist. So, if anything, someone with influence on the standard might suggest to reduce the maximum permitted frequency. Guenter