From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752291AbbLEECO (ORCPT ); Fri, 4 Dec 2015 23:02:14 -0500 Received: from mail-yk0-f170.google.com ([209.85.160.170]:34186 "EHLO mail-yk0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751791AbbLEECN (ORCPT ); Fri, 4 Dec 2015 23:02:13 -0500 MIME-Version: 1.0 In-Reply-To: References: <1449107584-3192-1-git-send-email-jwerner@chromium.org> Date: Fri, 4 Dec 2015 20:02:11 -0800 X-Google-Sender-Auth: _J49PvROHksHW09_APghSIRV8UE Message-ID: Subject: Re: [PATCH] RTC: RK808: Work around hardware bug on November 31st From: Doug Anderson To: Julius Werner Cc: Andrew Morton , Alessandro Zummo , Sonny Rao , Chris Zhong , 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 Fri, Dec 4, 2015 at 5:54 PM, Julius Werner wrote: >> How would such a hook work? If userspace sees the system suspend on >> Nov 30th and sees the system wake up on Dec 1st, how does it know >> whether it should adjust? If it's truly Dec 1st then the kernel will >> have adjusted the date from Nov 31st to Dec 1st. If it's truly Dec >> 2nd then the kernel will not have adjusted the date and the RTC will >> have ticked past Nov 31 and onto Dec 1st. Userspace can't tell. >> Userspace could try to parse "dmesg" and look to see if the kernel >> adjusted, but that's ugly. > > Good point, I didn't think that through far enough. I guess parsing > dmesg would be an option, but a pretty ugly one and it wouldn't be > guaranteed to work if you got an early boot kernel crash after the > correction. So, really, it seems like there's no reliable way to fix > this for S5 (unless we start doing crazy things like writing to disk > from kernel code). Hmmm, this made me think. We _do_ have some storage we could use, depending on how hacky^H^H^H^H^H^H clever we wanted to be. We've got the alarm registers in the RTC. If we set the alarm to something but then turn the alarm off then we can use that to store information that will persist in S5 (as long as the RTC is ticking). What do you think? I'd have to think of a scheme, but we could certainly use alarms that are several years in the future (or the past) as a sentinel, then use the day/month of the last time the kernel saw the time.... ...and speaking of the alarm, we also need to handle the RTC bug for setting the alarm. If you set an alarm for 10 seconds after Nov 30, you need to set the alarm for Nov 31st or it will actually fire 10 seconds + 1 day later. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yk0-x234.google.com (mail-yk0-x234.google.com. [2607:f8b0:4002:c07::234]) by gmr-mx.google.com with ESMTPS id m7si1385494ywe.1.2015.12.04.20.02.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 04 Dec 2015 20:02:12 -0800 (PST) Received: by mail-yk0-x234.google.com with SMTP id a77so144354490ykb.2 for ; Fri, 04 Dec 2015 20:02:12 -0800 (PST) MIME-Version: 1.0 Sender: rtc-linux@googlegroups.com In-Reply-To: References: <1449107584-3192-1-git-send-email-jwerner@chromium.org> Date: Fri, 4 Dec 2015 20:02:11 -0800 Message-ID: Subject: [rtc-linux] Re: [PATCH] RTC: RK808: Work around hardware bug on November 31st From: Doug Anderson To: Julius Werner Cc: Andrew Morton , Alessandro Zummo , Sonny Rao , Chris Zhong , 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 Fri, Dec 4, 2015 at 5:54 PM, Julius Werner wrote: >> How would such a hook work? If userspace sees the system suspend on >> Nov 30th and sees the system wake up on Dec 1st, how does it know >> whether it should adjust? If it's truly Dec 1st then the kernel will >> have adjusted the date from Nov 31st to Dec 1st. If it's truly Dec >> 2nd then the kernel will not have adjusted the date and the RTC will >> have ticked past Nov 31 and onto Dec 1st. Userspace can't tell. >> Userspace could try to parse "dmesg" and look to see if the kernel >> adjusted, but that's ugly. > > Good point, I didn't think that through far enough. I guess parsing > dmesg would be an option, but a pretty ugly one and it wouldn't be > guaranteed to work if you got an early boot kernel crash after the > correction. So, really, it seems like there's no reliable way to fix > this for S5 (unless we start doing crazy things like writing to disk > from kernel code). Hmmm, this made me think. We _do_ have some storage we could use, depending on how hacky^H^H^H^H^H^H clever we wanted to be. We've got the alarm registers in the RTC. If we set the alarm to something but then turn the alarm off then we can use that to store information that will persist in S5 (as long as the RTC is ticking). What do you think? I'd have to think of a scheme, but we could certainly use alarms that are several years in the future (or the past) as a sentinel, then use the day/month of the last time the kernel saw the time.... ...and speaking of the alarm, we also need to handle the RTC bug for setting the alarm. If you set an alarm for 10 seconds after Nov 30, you need to set the alarm for Nov 31st or it will actually fire 10 seconds + 1 day later. -- -- You received this message because you are subscribed to "rtc-linux". Membership options at http://groups.google.com/group/rtc-linux . Please read http://groups.google.com/group/rtc-linux/web/checklist before submitting a driver. --- You received this message because you are subscribed to the Google Groups "rtc-linux" group. 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