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[209.132.180.67]) by mx.google.com with ESMTP id f12si38317616pfh.257.2019.04.30.06.08.44; Tue, 30 Apr 2019 06:09:04 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727912AbfD3NFr (ORCPT + 99 others); Tue, 30 Apr 2019 09:05:47 -0400 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:42883 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726689AbfD3NFr (ORCPT ); Tue, 30 Apr 2019 09:05:47 -0400 X-Originating-IP: 109.213.14.175 Received: from localhost (alyon-652-1-31-175.w109-213.abo.wanadoo.fr [109.213.14.175]) (Authenticated sender: alexandre.belloni@bootlin.com) by relay3-d.mail.gandi.net (Postfix) with ESMTPSA id 97BEC60006; Tue, 30 Apr 2019 13:05:44 +0000 (UTC) Date: Tue, 30 Apr 2019 15:05:44 +0200 From: Alexandre Belloni To: Baruch Siach Cc: linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 2/4] rtc: digicolor: set range Message-ID: <20190430130544.GF11339@piout.net> References: <20190430093212.28425-1-alexandre.belloni@bootlin.com> <20190430093212.28425-2-alexandre.belloni@bootlin.com> <877ebbu3lz.fsf@tarshish> <20190430114702.GD11339@piout.net> <875zqvu1l3.fsf@tarshish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <875zqvu1l3.fsf@tarshish> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30/04/2019 15:20:08+0300, Baruch Siach wrote: > Hi Alexandre, > > On Tue, Apr 30 2019, Alexandre Belloni wrote: > > On 30/04/2019 14:36:24+0300, Baruch Siach wrote: > >> Hi Alexandre, > >> > >> On Tue, Apr 30 2019, Alexandre Belloni wrote: > >> > >> > While the range of REFERENCE + TIME is actually 33 bits, the counter > >> > itself (TIME) is a 32-bits seconds counter. > >> > > >> > Signed-off-by: Alexandre Belloni > >> > --- > >> > drivers/rtc/rtc-digicolor.c | 1 + > >> > 1 file changed, 1 insertion(+) > >> > > >> > diff --git a/drivers/rtc/rtc-digicolor.c b/drivers/rtc/rtc-digicolor.c > >> > index 5bb14c56bc9a..e6e16aaac254 100644 > >> > --- a/drivers/rtc/rtc-digicolor.c > >> > +++ b/drivers/rtc/rtc-digicolor.c > >> > @@ -206,6 +206,7 @@ static int __init dc_rtc_probe(struct platform_device *pdev) > >> > platform_set_drvdata(pdev, rtc); > >> > > >> > rtc->rtc_dev->ops = &dc_rtc_ops; > >> > + rtc->rtc_dev->range_max = U32_MAX; > >> > >> Where can I find documentation on the meaning and usage of the range_max > >> value? I could not find anything in the kernel source. > > > > It should be set to the maximum UNIX timestamp the RTC can be set to > > while keeping range_min to range_max contiguous. > > > > In the digicolor case, you could go up to 8589934590 (Wed Mar 16 > > 12:56:30 UTC 2242) but the driver only writes DC_RTC_REFERENCE and I'm > > not sure it can also update DC_RTC_TIME safely. > > DC_RTC_TIME resets to zero whenever dc_rtc_write writes CMD_RESET to the > DC_RTC_CONTROL register. DC_RTC_REFERENCE keeps the value that > dc_rtc_write stores there. So the driver will return values larger than > U32_MAX if you happen to cross this point in time between dc_rtc_write > and dc_rtc_read. But you can't store a value larger than U32_MAX in > DC_RTC_REFERENCE. > > Will the core RTC code handle the U32_MAX cross correctly? > Yes, this is ok to return a valid value that is higher than range_max. However, at that time, you will not be able to set any alarms anymore as the core doesn't allow to set alarms after range_max. I would think that this is fine because this will happen in 2106 and we have a way to offset the time (the whole goal of setting the range) using device tree. -- Alexandre Belloni, Bootlin Embedded Linux and Kernel engineering https://bootlin.com