Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751279AbbLUIQn (ORCPT ); Mon, 21 Dec 2015 03:16:43 -0500 Received: from down.free-electrons.com ([37.187.137.238]:60742 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751074AbbLUIQl (ORCPT ); Mon, 21 Dec 2015 03:16:41 -0500 Date: Mon, 21 Dec 2015 09:16:39 +0100 From: Alexandre Belloni To: Julius Werner Cc: Andrew Morton , Alessandro Zummo , Doug Anderson , Sonny Rao , Chris Zhong , Heiko Stuebner , linux-kernel@vger.kernel.org, rtc-linux@googlegroups.com Subject: Re: [PATCHv3] RTC: RK808: Compensate for Rockchip calendar deviation on November 31st Message-ID: <20151221081639.GF3541@piout.net> References: <1450220569-10670-1-git-send-email-jwerner@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1450220569-10670-1-git-send-email-jwerner@chromium.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6474 Lines: 144 On 15/12/2015 at 15:02:49 -0800, Julius Werner wrote : > In A.D. 1582 Pope Gregory XIII found that the existing Julian calendar > insufficiently represented reality, and changed the rules about > calculating leap years to account for this. Similarly, in A.D. 2013 > Rockchip hardware engineers found that the new Gregorian calendar still > contained flaws, and that the month of November should be counted up to > 31 days instead. Unfortunately it takes a long time for calendar changes > to gain widespread adoption, and just like more than 300 years went by > before the last Protestant nation implemented Greg's proposal, we will > have to wait a while until all religions and operating system kernels > acknowledge the inherent advantages of the Rockchip system. Until then > we need to translate dates read from (and written to) Rockchip hardware > back to the Gregorian format. > > This patch works by defining Jan 1st, 2016 as the arbitrary anchor date > on which Rockchip and Gregorian calendars are in sync. From that we can > translate arbitrary later dates back and forth by counting the number > of November/December transitons since the anchor date to determine the > offset between the calendars. We choose this method (rather than trying > to regularly "correct" the date stored in hardware) since it's the only > way to ensure perfect time-keeping even if the system may be shut down > for an unknown number of years. The drawback is that other software > reading the same hardware (e.g. mainboard firmware) must use the same > translation convention (including the same anchor date) to be able to > read and write correct timestamps from/to the RTC. > > Signed-off-by: Julius Werner I forgot to inform you but I've applied it and it landed in 4.4-rc6. > --- > drivers/rtc/rtc-rk808.c | 48 ++++++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 44 insertions(+), 4 deletions(-) > > diff --git a/drivers/rtc/rtc-rk808.c b/drivers/rtc/rtc-rk808.c > index 91ca0bc..35c9aad 100644 > --- a/drivers/rtc/rtc-rk808.c > +++ b/drivers/rtc/rtc-rk808.c > @@ -56,6 +56,42 @@ struct rk808_rtc { > int irq; > }; > > +/* > + * The Rockchip calendar used by the RK808 counts November with 31 days. We use > + * these translation functions to convert its dates to/from the Gregorian > + * calendar used by the rest of the world. We arbitrarily define Jan 1st, 2016 > + * as the day when both calendars were in sync, and treat all other dates > + * relative to that. > + * NOTE: Other system software (e.g. firmware) that reads the same hardware must > + * implement this exact same conversion algorithm, with the same anchor date. > + */ > +static time64_t nov2dec_transitions(struct rtc_time *tm) > +{ > + return (tm->tm_year + 1900) - 2016 + (tm->tm_mon + 1 > 11 ? 1 : 0); > +} > + > +static void rockchip_to_gregorian(struct rtc_time *tm) > +{ > + /* If it's Nov 31st, rtc_tm_to_time64() will count that like Dec 1st */ > + time64_t time = rtc_tm_to_time64(tm); > + rtc_time64_to_tm(time + nov2dec_transitions(tm) * 86400, tm); > +} > + > +static void gregorian_to_rockchip(struct rtc_time *tm) > +{ > + time64_t extra_days = nov2dec_transitions(tm); > + time64_t time = rtc_tm_to_time64(tm); > + rtc_time64_to_tm(time - extra_days * 86400, tm); > + > + /* Compensate if we went back over Nov 31st (will work up to 2381) */ > + if (nov2dec_transitions(tm) < extra_days) { > + if (tm->tm_mon + 1 == 11) > + tm->tm_mday++; /* This may result in 31! */ > + else > + rtc_time64_to_tm(time - (extra_days - 1) * 86400, tm); > + } > +} > + > /* Read current time and date in RTC */ > static int rk808_rtc_readtime(struct device *dev, struct rtc_time *tm) > { > @@ -101,9 +137,10 @@ static int rk808_rtc_readtime(struct device *dev, struct rtc_time *tm) > tm->tm_mon = (bcd2bin(rtc_data[4] & MONTHS_REG_MSK)) - 1; > tm->tm_year = (bcd2bin(rtc_data[5] & YEARS_REG_MSK)) + 100; > tm->tm_wday = bcd2bin(rtc_data[6] & WEEKS_REG_MSK); > + rockchip_to_gregorian(tm); > dev_dbg(dev, "RTC date/time %4d-%02d-%02d(%d) %02d:%02d:%02d\n", > 1900 + tm->tm_year, tm->tm_mon + 1, tm->tm_mday, > - tm->tm_wday, tm->tm_hour , tm->tm_min, tm->tm_sec); > + tm->tm_wday, tm->tm_hour, tm->tm_min, tm->tm_sec); > > return ret; > } > @@ -116,6 +153,10 @@ static int rk808_rtc_set_time(struct device *dev, struct rtc_time *tm) > u8 rtc_data[NUM_TIME_REGS]; > int ret; > > + dev_dbg(dev, "set RTC date/time %4d-%02d-%02d(%d) %02d:%02d:%02d\n", > + 1900 + tm->tm_year, tm->tm_mon + 1, tm->tm_mday, > + tm->tm_wday, tm->tm_hour, tm->tm_min, tm->tm_sec); > + gregorian_to_rockchip(tm); > rtc_data[0] = bin2bcd(tm->tm_sec); > rtc_data[1] = bin2bcd(tm->tm_min); > rtc_data[2] = bin2bcd(tm->tm_hour); > @@ -123,9 +164,6 @@ static int rk808_rtc_set_time(struct device *dev, struct rtc_time *tm) > rtc_data[4] = bin2bcd(tm->tm_mon + 1); > rtc_data[5] = bin2bcd(tm->tm_year - 100); > rtc_data[6] = bin2bcd(tm->tm_wday); > - dev_dbg(dev, "set RTC date/time %4d-%02d-%02d(%d) %02d:%02d:%02d\n", > - 1900 + tm->tm_year, tm->tm_mon + 1, tm->tm_mday, > - tm->tm_wday, tm->tm_hour , tm->tm_min, tm->tm_sec); > > /* Stop RTC while updating the RTC registers */ > ret = regmap_update_bits(rk808->regmap, RK808_RTC_CTRL_REG, > @@ -170,6 +208,7 @@ static int rk808_rtc_readalarm(struct device *dev, struct rtc_wkalrm *alrm) > alrm->time.tm_mday = bcd2bin(alrm_data[3] & DAYS_REG_MSK); > alrm->time.tm_mon = (bcd2bin(alrm_data[4] & MONTHS_REG_MSK)) - 1; > alrm->time.tm_year = (bcd2bin(alrm_data[5] & YEARS_REG_MSK)) + 100; > + rockchip_to_gregorian(&alrm->time); > > ret = regmap_read(rk808->regmap, RK808_RTC_INT_REG, &int_reg); > if (ret) { > @@ -227,6 +266,7 @@ static int rk808_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm) > alrm->time.tm_mday, alrm->time.tm_wday, alrm->time.tm_hour, > alrm->time.tm_min, alrm->time.tm_sec); > > + gregorian_to_rockchip(&alrm->time); > alrm_data[0] = bin2bcd(alrm->time.tm_sec); > alrm_data[1] = bin2bcd(alrm->time.tm_min); > alrm_data[2] = bin2bcd(alrm->time.tm_hour); > -- > 2.1.2 > -- Alexandre Belloni, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com -- 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/