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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 7C3B8C4338F for ; Tue, 17 Aug 2021 13:21:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 554F060F22 for ; Tue, 17 Aug 2021 13:21:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237407AbhHQNVk (ORCPT ); Tue, 17 Aug 2021 09:21:40 -0400 Received: from relay12.mail.gandi.net ([217.70.178.232]:51071 "EHLO relay12.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235267AbhHQNVj (ORCPT ); Tue, 17 Aug 2021 09:21:39 -0400 Received: (Authenticated sender: alexandre.belloni@bootlin.com) by relay12.mail.gandi.net (Postfix) with ESMTPSA id 53CB8200004; Tue, 17 Aug 2021 13:21:03 +0000 (UTC) Date: Tue, 17 Aug 2021 15:21:03 +0200 From: Alexandre Belloni To: tonywwang-oc@zhaoxin.com Cc: a.zummo@towertech.it, linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org, TimGuo-oc@zhaoxin.com, CooperYan@zhaoxin.com, QiyuanWang@zhaoxin.com, HerryYang@zhaoxin.com, CobeChen@zhaoxin.com, YanchenSun@zhaoxin.com Subject: Re: [PATCH] rtc: Fix set RTC time delay 500ms on some Zhaoxin SOCs Message-ID: References: <1629121638-3246-1-git-send-email-TonyWWang-oc@zhaoxin.com> <7EA395FF-EB66-4274-9EDE-EC28450A0259@zhaoxin.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7EA395FF-EB66-4274-9EDE-EC28450A0259@zhaoxin.com> Precedence: bulk List-ID: X-Mailing-List: linux-rtc@vger.kernel.org On 17/08/2021 19:09:28+0800, tonywwang-oc@zhaoxin.com wrote: > > > On August 16, 2021 8:36:48 PM GMT+08:00, Alexandre Belloni wrote: > >On 16/08/2021 18:03:13+0800, Tony W Wang-oc wrote: > >> > >> On 16/08/2021 16:24, Alexandre Belloni wrote: > >> > Hello, > >> > > >> > On 16/08/2021 21:47:18+0800, Tony W Wang-oc wrote: > >> >> When the RTC divider is changed from reset to an operating time > >base, > >> >> the first update cycle should be 500ms later. But on some Zhaoxin > >SOCs, > >> >> this first update cycle is one second later. > >> >> > >> >> So set RTC time on these Zhaoxin SOCs will causing 500ms delay. > >> >> > >> > > >> > Can you explain what is the relationship between writing the > >divider and > >> > the 500ms delay? > >> >> Isn't the issue that you are using systohc and set_offset_nsec is > >set to > >> > NSEC_PER_SEC / 2 ? > >> > > >> No. > >> When using #hwclock -s to set RTC time and set_offset_nsec is > >> NSEC_PER_SEC / 2, the function mc146818_set_time() requires the first > >> update cycle after RTC divider be changed from reset to an operating > >> mode is 500ms as the MC146818A spec specified. But on some Zhaoxin > >SOCs, > >> the first update cycle of RTC is one second later after RTC divider > >be > >> changed from reset to an operating mode. So the first update cycle > >after > >> RTC divider be changed from reset to an operation mode on These SOCs > >> will causing 500ms delay with current mc146818_set_time() > >implementation. > >> > > > >What happens with hwclock --delay=0 -s ? > > With "hwclock --delay=0 -s" still have this problem. Actually, this 500ms delay caused by writing the RTC time on these Zhaoxin SOCs. > As I've tested, with hwclock --delay=0 -w can fix it too. > Both -s and -w end up calling set_hardware_clock_exact() so both should end up with the correct time. If this is not the case, then hwclock needs to be fixed. -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com