Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755229AbbLGCum (ORCPT ); Sun, 6 Dec 2015 21:50:42 -0500 Received: from mail-yk0-f170.google.com ([209.85.160.170]:33969 "EHLO mail-yk0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755091AbbLGCuk (ORCPT ); Sun, 6 Dec 2015 21:50:40 -0500 MIME-Version: 1.0 In-Reply-To: <5664E1CF.8030406@rock-chips.com> References: <1449107584-3192-1-git-send-email-jwerner@chromium.org> <5664E1CF.8030406@rock-chips.com> Date: Sun, 6 Dec 2015 18:50:39 -0800 X-Google-Sender-Auth: vfA2qChFql_3qh32jDTjxcQXDDk Message-ID: Subject: Re: [PATCH] RTC: RK808: Work around hardware bug on November 31st From: Doug Anderson To: Chris Zhong Cc: Julius Werner , Andrew Morton , Alessandro Zummo , Sonny Rao , Heiko Stuebner , "linux-kernel@vger.kernel.org" , rtc-linux@googlegroups.com Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1818 Lines: 47 Chris, On Sun, Dec 6, 2015 at 5:33 PM, Chris Zhong wrote: > Hi Doug > > RK808 has a shadowed register for saving a "frozen" RTC time. > When we setting "GET_TIME" to 1, the time will save in this shadowed > register. So if we do not set the "GET_TIME", we always get the last time. > > read the old time before "get_time", and then read the time again for new > time. If the old time earlier than 12.1 && new time later than 12.1, we > should > +1 day for the correct rtc time. > > On the other hand, we should set the "GET_TIME" after rk808_rtc_set_time, > for restore the time before suspend/shut_down. Ah, good idea using the shadow registers. The whole point of the shadow registers is to enable atomic read of time, right? So if the clock ticks as you are reading 23:59:59 you don't end up reading 23:59:00 or 24:59:59 (you'll get either 23:59:59 or 24:00:00). So right, time read will now be: 1. Read GET_TIME. Confirm it's 1. 2. Read the time. 3. Set GET_TIME to 0. 4. Set GET_TIME to 1. 5. Read the time. If time from #2 < 11/31 and time from #5 >= 11/31 then we do the adjust. If GET_TIME wasn't 1 in step #1 then we won't do any adjusting unless the time is actually 11/31. Between steps #4 and #5 we'll need to add a small delay since old code used to use the setting to 0 as a delay (as commented). We should presumably always leave GET_TIME as 1 unless we're actively reading the time for the most reliability. Also, if we've already read the time this bootup, we can certainly optimize the above by skipping #1 and #2. -Doug -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/