From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755321AbbLGCwY (ORCPT ); Sun, 6 Dec 2015 21:52:24 -0500 Received: from mail-yk0-f176.google.com ([209.85.160.176]:35363 "EHLO mail-yk0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755095AbbLGCwX (ORCPT ); Sun, 6 Dec 2015 21:52:23 -0500 MIME-Version: 1.0 In-Reply-To: References: <1449107584-3192-1-git-send-email-jwerner@chromium.org> <5664E1CF.8030406@rock-chips.com> Date: Sun, 6 Dec 2015 18:52:22 -0800 X-Google-Sender-Auth: nMPI8C7DsBafRaPSTNi1K4ek_K4 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 Hi, On Sun, Dec 6, 2015 at 6:50 PM, Doug Anderson wrote: > 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. Oh, but also we still need to know whether to adjust the alarm. I think you said that all existing rk808 chips have this bug and that you'll set a bit (to be determined later) if/when this bug is fixed. So we still need to assume that all rk808 chips have this bug... -Doug From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-x22c.google.com (mail-yk0-x22c.google.com. [2607:f8b0:4002:c07::22c]) by gmr-mx.google.com with ESMTPS id p4si1986965ywc.6.2015.12.06.18.52.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 06 Dec 2015 18:52:22 -0800 (PST) Received: by mail-yk0-x22c.google.com with SMTP id r82so180246576ykd.3 for ; Sun, 06 Dec 2015 18:52:22 -0800 (PST) MIME-Version: 1.0 Sender: rtc-linux@googlegroups.com In-Reply-To: References: <1449107584-3192-1-git-send-email-jwerner@chromium.org> <5664E1CF.8030406@rock-chips.com> Date: Sun, 6 Dec 2015 18:52:22 -0800 Message-ID: Subject: [rtc-linux] 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 Reply-To: rtc-linux@googlegroups.com List-ID: List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , Hi, On Sun, Dec 6, 2015 at 6:50 PM, Doug Anderson wrote: > 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. Oh, but also we still need to know whether to adjust the alarm. I think you said that all existing rk808 chips have this bug and that you'll set a bit (to be determined later) if/when this bug is fixed. So we still need to assume that all rk808 chips have this bug... -Doug -- -- You received this message because you are subscribed to "rtc-linux". Membership options at http://groups.google.com/group/rtc-linux . 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