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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 25B81C5CFE7 for ; Tue, 10 Jul 2018 01:17:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CFDF620881 for ; Tue, 10 Jul 2018 01:17:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CFDF620881 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=telegraphics.com.au Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754640AbeGJBR0 (ORCPT ); Mon, 9 Jul 2018 21:17:26 -0400 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:39306 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754581AbeGJBRT (ORCPT ); Mon, 9 Jul 2018 21:17:19 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by kvm5.telegraphics.com.au (Postfix) with ESMTP id 8708D22D6B; Mon, 9 Jul 2018 21:17:11 -0400 (EDT) Date: Tue, 10 Jul 2018 11:18:34 +1000 (AEST) From: Finn Thain To: Arnd Bergmann cc: Meelis Roos , Mathieu Malaterre , Paul Mackerras , Michael Ellerman , Geert Uytterhoeven , Joshua Thompson , Benjamin Herrenschmidt , Greg Ungerer , linux-m68k@vger.kernel.org, linuxppc-dev , LKML , y2038 Mailman List , Andreas Schwab Subject: Re: [PATCH 1/3] [v2] powerpc: mac: fix rtc read/write functions In-Reply-To: Message-ID: References: <20180619140229.3615110-1-arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 9 Jul 2018, Arnd Bergmann wrote: > > The most likely explanation I have here is that the RTC was indeed set > to an incorrect date, either because of a depleted battery (not unlikely > for a ~15 year old box) or because it was previously stored incorrectly. The PowerMac stores the GMT offset in NVRAM, and this gets used to initialize timezone_offset. If timezone_offset was negative and now.tv_sec was zero, I think this could store a 1969 date in the RTC: int update_persistent_clock64(struct timespec64 now) { struct rtc_time tm; if (!ppc_md.set_rtc_time) return -ENODEV; rtc_time64_to_tm(now.tv_sec + 1 + timezone_offset, &tm); return ppc_md.set_rtc_time(&tm); } But maybe now.tv_sec can be shown to be greater than timezone_offset. Then, what would happen when the timezone in /etc/localtime disagrees with the timezone_offset stored in NVRAM (PRAM)? Besides that, if the battery went flat, what use is a backtrace? Why not scrap the WARN_ON()? --