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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hLSSQ-0001Lf-1W; Tue, 30 Apr 2019 13:06:02 +0000 Received: from relay3-d.mail.gandi.net ([217.70.183.195]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1hLSSI-0001KX-Vr for linux-arm-kernel@lists.infradead.org; Tue, 30 Apr 2019 13:06:01 +0000 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 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-Disposition: inline In-Reply-To: <875zqvu1l3.fsf@tarshish> User-Agent: Mutt/1.11.3 (2019-02-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190430_060557_110277_AA0BC471 X-CRM114-Status: GOOD ( 24.46 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel