From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0E3E6C32792 for ; Thu, 3 Oct 2019 14:11:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E3F2A215EA for ; Thu, 3 Oct 2019 14:11:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730054AbfJCOLG (ORCPT ); Thu, 3 Oct 2019 10:11:06 -0400 Received: from mail-out.m-online.net ([212.18.0.9]:54451 "EHLO mail-out.m-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728405AbfJCOLF (ORCPT ); Thu, 3 Oct 2019 10:11:05 -0400 Received: from frontend01.mail.m-online.net (unknown [192.168.8.182]) by mail-out.m-online.net (Postfix) with ESMTP id 46kZft3hGJz1rLFn; Thu, 3 Oct 2019 16:11:02 +0200 (CEST) Received: from localhost (dynscan1.mnet-online.de [192.168.6.70]) by mail.m-online.net (Postfix) with ESMTP id 46kZft3G0yz1qqkM; Thu, 3 Oct 2019 16:11:02 +0200 (CEST) X-Virus-Scanned: amavisd-new at mnet-online.de Received: from mail.mnet-online.de ([192.168.8.182]) by localhost (dynscan1.mail.m-online.net [192.168.6.70]) (amavisd-new, port 10024) with ESMTP id 8_DMiCrKeOt7; Thu, 3 Oct 2019 16:11:01 +0200 (CEST) X-Auth-Info: DWv8BxMh/iTf0m4AnKrtt6dC4KfTKDUDo8wYmzBiBN4= Received: from jawa (85-222-111-42.dynamic.chello.pl [85.222.111.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.mnet-online.de (Postfix) with ESMTPSA; Thu, 3 Oct 2019 16:11:01 +0200 (CEST) Date: Thu, 3 Oct 2019 16:10:53 +0200 From: Lukasz Majewski To: Alexandre Belloni Cc: Alessandro Zummo , linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] rtc: Add support for century bits to m41t62 (rv4162) RTC devices Message-ID: <20191003161054.1eeae401@jawa> In-Reply-To: <20191003134329.GB575@piout.net> References: <20190911154803.15969-1-lukma@denx.de> <20191003114831.GR4106@piout.net> <20191003142150.3d73a9d7@jawa> <20191003123538.GS4106@piout.net> <20191003151434.49762715@jawa> <20191003134329.GB575@piout.net> Organization: denx.de X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; boundary="Sig_/hLnbrGCehw8PWPNow57OW+W"; protocol="application/pgp-signature" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Sig_/hLnbrGCehw8PWPNow57OW+W Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Hi Alexandre, > On 03/10/2019 15:14:34+0200, Lukasz Majewski wrote: > > Hi Alexandre, > > =20 > > > On 03/10/2019 14:21:50+0200, Lukasz Majewski wrote: =20 > > > > >=20 > > > > > See the datasheet: > > > > >=20 > > > > > "During any year which is a multiple of 4, the RV-4162 RTC > > > > > will automatically insert leap day, February 29. Therefore, > > > > > the application software must correct for this during the > > > > > exception years (2100, 2200, etc.) as noted above." =20 > > > >=20 > > > > I'm wondering what the phrase "application software" means here? > > > >=20 > > > > If it is the userland SW, then we shall at least be able to set > > > > 2099 in this device and then count on software correction. > > > >=20 > > > > If the "application software" is the kernel driver - the date > > > > correction shall be done there (maybe some lookup table?). > > > >=20 > > > > Personally, I do prefer the first option - this means that with > > > > this patch we can set the time to e.g. 2234 year and then rely > > > > on userland software (or libc) to do the correction. > > > > =20 > > >=20 > > > It is not possible to ensure this correction is properly done in > > > software, there is no point in letting the user set those bits. Sorry, but I do see some inconsistency here. The application note [1] says that the correction shall be done in application SW. The rtc-range.c program [2] sets and reads the time via ioctl (e.g. RTC_SET_TIME, RTC_RD_TIME). To pass your tests one needs to do the correction in linux kernel driver for drivers/rtc/rtc-m41t80.c.=20 Please correct me if I'm wrong, but IMHO it shall be enough to adjust 2100, 2200, 2300, years in this driver (the submitted patch shall be adjusted to support it - I can prepare proper v2). > > >=20 > > > =20 > >=20 > > I see your point. > >=20 > > However, could you share your idea on testing setting RTC time to > > year 2100 on this particular IC (by using hctosys and friends)? > > =20 >=20 > You can use rtc from > https://git.kernel.org/pub/scm/linux/kernel/git/abelloni/rtc-tools.git/ >=20 > You can also use rtc-range with your patch to observe that it fails in > 2100. Thanks for sharing useful links. >=20 Note: [1] - https://www.microcrystal.com/fileadmin/Media/Products/RTC/App.Manual/RV-416= 2-C7_App-Manual.pdf (point 4.5 and 4.6). [2] - https://git.kernel.org/pub/scm/linux/kernel/git/abelloni/rtc-tools.git/tree= /rtc-range.c Best regards, Lukasz Majewski -- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de --Sig_/hLnbrGCehw8PWPNow57OW+W Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEgAyFJ+N6uu6+XupJAR8vZIA0zr0FAl2WAW4ACgkQAR8vZIA0 zr08Kwf/YpzxMFrU14J1/zeQIdS2HX0KnJxnEjRfICLoEhuetfa4cjxXlSww7O3x 6ErhNA2wvBwZKwABeufpN8aSUdAsRiwCTQojyzd2RBvuCokZz38SbEP3KgKc8XhU Z1sU/ASmBUd1KpSkH/A6FysimfnU7qxJN+HdxXJyX/SDEsQFAKq0WAcV72Oylr9q b+SgFhoy1QxKspTZcblhw4th1hiDSiYvz358l+HuDu66mTyxEEDASID3Gmyd9TV4 8HYNwpvyaJPgyRiDwqqYbrZ7LVqSt8wBnPHoNaLEZXqVWXJBDRgVmMvlTZjYqOWS bm2oxVT/vNcORJc0DF9T4Ds4BTKy9w== =HmuE -----END PGP SIGNATURE----- --Sig_/hLnbrGCehw8PWPNow57OW+W--