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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 2D857C4332F for ; Sun, 12 Sep 2021 12:43:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 13AD261050 for ; Sun, 12 Sep 2021 12:43:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235086AbhILMob (ORCPT ); Sun, 12 Sep 2021 08:44:31 -0400 Received: from mx-out.tlen.pl ([193.222.135.148]:46644 "EHLO mx-out.tlen.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235262AbhILMo3 (ORCPT ); Sun, 12 Sep 2021 08:44:29 -0400 Received: (wp-smtpd smtp.tlen.pl 9149 invoked from network); 12 Sep 2021 14:43:12 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=o2.pl; s=1024a; t=1631450592; bh=7IdaZZIuiekG92mGZkWkTZhUEs0esuhAH7fpWv5Xq/0=; h=From:To:Cc:Subject; b=us/VXs6EY9xS8I4zkWtPNckJ5Hl3j5eSv3sMfgKlSt7XYl0SLnffMTc0VYoyAkEvS bMho4I9dawtbg1T5KS6rml20C36UeZAaeiFpT5dxuq3yzfVwxD+VLgNzyQGejvVuaz ry1xUJheSZvXmd2ld5AAyNsyHiV7k/VCn19TtDM8= Received: from aafh223.neoplus.adsl.tpnet.pl (HELO localhost.localdomain) (mat.jonczyk@o2.pl@[83.4.137.223]) (envelope-sender ) by smtp.tlen.pl (WP-SMTPD) with SMTP for ; 12 Sep 2021 14:43:12 +0200 From: =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= To: linux-rtc@vger.kernel.org Cc: =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= , Alessandro Zummo , Alexandre Belloni , stable@vger.kernel.org Subject: [PATCH 2/7] rtc-cmos: dont touch alarm registers during update Date: Sun, 12 Sep 2021 14:42:09 +0200 Message-Id: <20210912124214.81853-3-mat.jonczyk@o2.pl> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210912124214.81853-1-mat.jonczyk@o2.pl> References: <20210912124214.81853-1-mat.jonczyk@o2.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-WP-MailID: b94cd8216409147ba8bac3b1c3fed031 X-WP-AV: skaner antywirusowy Poczty o2 X-WP-SPAM: NO 0000000 [wfOE] Precedence: bulk List-ID: X-Mailing-List: linux-rtc@vger.kernel.org Some Intel chipsets disconnect the time and date RTC registers when the clock update is in progress: during this time reads may return bogus values and writes fail silently. This includes the RTC alarm registers. [1] cmos_read_alarm() and cmos_set_alarm() did not take account for that, which caused alarm time reads to sometimes return bogus values. This can be shown with a test patch that I am attaching to this patch series. Setting the alarm clock also probably did fail sometimes. To make this patch suitable for inclusion in stable kernels, I'm using a simple method for avoiding the RTC update cycle. This method is used in mach_set_rtc_mmss() in arch/x86/kernel/rtc.c. A more elaborate algorithm - as in mc146818_get_time() in drivers/rtc/rtc-mc146818-lib.c - would be too complcated for stable. [2] cmos_wait_for_uip_clear() has the rtc_lock taken while waiting for the UIP bit to become clear. This should be harmless as during the UIP the RTC cannot be read from anyway. mach_get_cmos_time() in arch/x86/kernel/rtc.c does things the same way. [1] 7th Generation Intel ® Processor Family I/O for U/Y Platforms [...] Datasheet, Volume 1 of 2 (Intel's Document Number: 334658-006) Page 208 https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/7th-and-8th-gen-core-family-mobile-u-y-processor-lines-i-o-datasheet-vol-1.pdf "If a RAM read from the ten time and date bytes is attempted during an update cycle, the value read do not necessarily represent the true contents of those locations. Any RAM writes under the same conditions are ignored.' [2] I'm going to submit a unification patch for a later kernel release - prefer to see this in stable. Signed-off-by: Mateusz Jończyk Cc: Alessandro Zummo Cc: Alexandre Belloni Cc: stable@vger.kernel.org --- drivers/rtc/rtc-cmos.c | 38 ++++++++++++++++++++++++++++++++++++-- 1 file changed, 36 insertions(+), 2 deletions(-) diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c index 2cd0fe728ab2..643433d984ab 100644 --- a/drivers/rtc/rtc-cmos.c +++ b/drivers/rtc/rtc-cmos.c @@ -248,6 +248,31 @@ static int cmos_set_time(struct device *dev, struct rtc_time *t) return mc146818_set_time(t); } +/* Some Intel chipsets disconnect the alarm registers when the clock update is + * in progress - during this time reads return bogus values and writes may fail + * silently. See for example "7th Generation Intel® Processor Family I/O for + * U/Y Platforms [...] Datasheet", section 27.7.1 + * + * Check the UIP bit to prevent this, waiting for max 10ms for it to become + * clear. + * + * This function has to be called with rtc_lock taken. + */ +static int cmos_wait_for_uip_clear(struct device *dev) +{ + int i; + + for (i = 0; i < 100; i++) { + if ((CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) == 0) + return 0; + udelay(100); + } + + dev_warn_ratelimited(dev, "UIP bit is stuck, cannot access RTC registers\n"); + + return 1; +} + static int cmos_read_alarm(struct device *dev, struct rtc_wkalrm *t) { struct cmos_rtc *cmos = dev_get_drvdata(dev); @@ -257,12 +282,17 @@ static int cmos_read_alarm(struct device *dev, struct rtc_wkalrm *t) if (!is_valid_irq(cmos->irq)) return -EIO; + spin_lock_irq(&rtc_lock); + + if (cmos_wait_for_uip_clear(dev)) { + spin_unlock_irq(&rtc_lock); + return -EIO; + } + /* Basic alarms only support hour, minute, and seconds fields. * Some also support day and month, for alarms up to a year in * the future. */ - - spin_lock_irq(&rtc_lock); t->time.tm_sec = CMOS_READ(RTC_SECONDS_ALARM); t->time.tm_min = CMOS_READ(RTC_MINUTES_ALARM); t->time.tm_hour = CMOS_READ(RTC_HOURS_ALARM); @@ -477,6 +507,10 @@ static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t) } spin_lock_irq(&rtc_lock); + if (cmos_wait_for_uip_clear(dev)) { + spin_unlock_irq(&rtc_lock); + return -EIO; + } /* next rtc irq must not be from previous alarm setting */ cmos_irq_disable(cmos, RTC_AIE); -- 2.25.1