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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C912C433EF for ; Sat, 30 Oct 2021 21:47:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E516260E54 for ; Sat, 30 Oct 2021 21:47:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232025AbhJ3VuD (ORCPT ); Sat, 30 Oct 2021 17:50:03 -0400 Received: from mx-out.tlen.pl ([193.222.135.142]:28752 "EHLO mx-out.tlen.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231993AbhJ3VuC (ORCPT ); Sat, 30 Oct 2021 17:50:02 -0400 Received: (wp-smtpd smtp.tlen.pl 21608 invoked from network); 30 Oct 2021 23:47:28 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=o2.pl; s=1024a; t=1635630449; bh=5TaYnfCf1/DpvlsF3hi5y8tCZweGamTMxI3hlk6QjzY=; h=From:To:Cc:Subject; b=fHOfGPpvrN6aZJqasa+hh+NZ/8Uhr6A4avXfCiw/Akyr76VJwzvagSMC3UGowv8Qt PPh4EiLd55OOY7z5r7bGVPMwgrlc0gyoWBD9FVArdqnnFm9Tfji+Y0jC80G4XU8gl7 NZQ+fzsipjuqTuN8OOP41poUh1QckWKyaqsfqUPA= Received: from ablz112.neoplus.adsl.tpnet.pl (HELO localhost.localdomain) (mat.jonczyk@o2.pl@[83.7.219.112]) (envelope-sender ) by smtp.tlen.pl (WP-SMTPD) with SMTP for ; 30 Oct 2021 23:47:28 +0200 From: =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= To: linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Mateusz=20Jo=C5=84czyk?= , Thomas Gleixner , Alessandro Zummo , Alexandre Belloni Subject: [PATCH v3 2/7] rtc-mc146818-lib: fix RTC presence check Date: Sat, 30 Oct 2021 23:46:30 +0200 Message-Id: <20211030214636.49602-3-mat.jonczyk@o2.pl> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211030214636.49602-1-mat.jonczyk@o2.pl> References: <20211030214636.49602-1-mat.jonczyk@o2.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-WP-MailID: 7a1b4dbbb9051338445264f4abca4134 X-WP-AV: skaner antywirusowy Poczty o2 X-WP-SPAM: NO 0000000 [gaO0] Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org To prevent an infinite loop in mc146818_get_time(), commit 211e5db19d15 ("rtc: mc146818: Detect and handle broken RTCs") added a check for RTC availability. Together with a later fix, it checked if bit 6 in register 0x0d is cleared. This, however, caused a false negative on a motherboard with an AMD SB710 southbridge; according to the specification [1], bit 6 of register 0x0d of this chipset is a scratchbit. This caused a regression in Linux 5.11 - the RTC was determined broken by the kernel and not used by rtc-cmos.c [3]. As a better alternative, check whether the UIP ("Update-in-progress") bit is set for longer then 10ms. If that is the case, then apparently the RTC is either absent (and all register reads return 0xff) or broken. Also limit the number of loop iterations in mc146818_get_time() to 10 to prevent an infinite loop there. In a previous approach to this problem, I implemented a check whether the RTC_HOURS register contains a value <= 24. This, however, sometimes did not work correctly on my Intel Kaby Lake laptop. According to Intel's documentation [2], "the time and date RAM locations (0-9) are disconnected from the external bus" during the update cycle so reading this register without checking the UIP bit is incorrect. [1] AMD SB700/710/750 Register Reference Guide, page 308, https://developer.amd.com/wordpress/media/2012/10/43009_sb7xx_rrg_pub_1.00.pdf [2] 7th Generation Intel ® Processor Family I/O for U/Y Platforms [...] Datasheet Volume 1 of 2, page 209 Intel's Document Number: 334658-006, 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 [3] Functions in arch/x86/kernel/rtc.c apparently were using it. Fixes: 211e5db19d15 ("rtc: mc146818: Detect and handle broken RTCs") Fixes: ebb22a059436 ("rtc: mc146818: Dont test for bit 0-5 in Register D") Signed-off-by: Mateusz Jończyk Cc: Thomas Gleixner Cc: Alessandro Zummo Cc: Alexandre Belloni v2: Tweak commit description, remove "Cc: stable" (I'll send it manually after more regression testing). v3: - add "EXPORT_SYMBOL_GPL(mc146818_does_rtc_work)", - change return type from mc146818_does_rtc_work to bool --- drivers/rtc/rtc-cmos.c | 10 ++++------ drivers/rtc/rtc-mc146818-lib.c | 35 ++++++++++++++++++++++++++++++---- include/linux/mc146818rtc.h | 1 + 3 files changed, 36 insertions(+), 10 deletions(-) diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c index dc3f8b0dde98..9404f58ee01d 100644 --- a/drivers/rtc/rtc-cmos.c +++ b/drivers/rtc/rtc-cmos.c @@ -793,16 +793,14 @@ cmos_do_probe(struct device *dev, struct resource *ports, int rtc_irq) rename_region(ports, dev_name(&cmos_rtc.rtc->dev)); - spin_lock_irq(&rtc_lock); - - /* Ensure that the RTC is accessible. Bit 6 must be 0! */ - if ((CMOS_READ(RTC_VALID) & 0x40) != 0) { - spin_unlock_irq(&rtc_lock); - dev_warn(dev, "not accessible\n"); + if (!mc146818_does_rtc_work()) { + dev_warn(dev, "broken or not accessible\n"); retval = -ENXIO; goto cleanup1; } + spin_lock_irq(&rtc_lock); + if (!(flags & CMOS_RTC_FLAGS_NOFREQ)) { /* force periodic irq to CMOS reset default of 1024Hz; * diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c index dcfaf09946ee..b50612ce1a6d 100644 --- a/drivers/rtc/rtc-mc146818-lib.c +++ b/drivers/rtc/rtc-mc146818-lib.c @@ -8,10 +8,36 @@ #include #endif +/* + * If the UIP (Update-in-progress) bit of the RTC is set for more then + * 10ms, the RTC is apparently broken or not present. + */ +bool mc146818_does_rtc_work(void) +{ + int i; + unsigned char val; + unsigned long flags; + + for (i = 0; i < 10; i++) { + spin_lock_irqsave(&rtc_lock, flags); + val = CMOS_READ(RTC_FREQ_SELECT); + spin_unlock_irqrestore(&rtc_lock, flags); + + if ((val & RTC_UIP) == 0) + return true; + + mdelay(1); + } + + return false; +} +EXPORT_SYMBOL_GPL(mc146818_does_rtc_work); + unsigned int mc146818_get_time(struct rtc_time *time) { unsigned char ctrl; unsigned long flags; + unsigned int iter_count = 0; unsigned char century = 0; bool retry; @@ -20,13 +46,14 @@ unsigned int mc146818_get_time(struct rtc_time *time) #endif again: - spin_lock_irqsave(&rtc_lock, flags); - /* Ensure that the RTC is accessible. Bit 6 must be 0! */ - if (WARN_ON_ONCE((CMOS_READ(RTC_VALID) & 0x40) != 0)) { - spin_unlock_irqrestore(&rtc_lock, flags); + if (iter_count > 10) { + pr_err_ratelimited("Unable to read current time from RTC\n"); memset(time, 0xff, sizeof(*time)); return 0; } + iter_count++; + + spin_lock_irqsave(&rtc_lock, flags); /* * Check whether there is an update in progress during which the diff --git a/include/linux/mc146818rtc.h b/include/linux/mc146818rtc.h index 0661af17a758..69c80c4325bf 100644 --- a/include/linux/mc146818rtc.h +++ b/include/linux/mc146818rtc.h @@ -123,6 +123,7 @@ struct cmos_rtc_board_info { #define RTC_IO_EXTENT_USED RTC_IO_EXTENT #endif /* ARCH_RTC_LOCATION */ +bool mc146818_does_rtc_work(void); unsigned int mc146818_get_time(struct rtc_time *time); int mc146818_set_time(struct rtc_time *time); -- 2.25.1