From patchwork Fri Jan 7 15:34:54 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Mateusz_Jo=C5=84czyk?= X-Patchwork-Id: 1576672 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: bilbo.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=o2.pl header.i=@o2.pl header.a=rsa-sha256 header.s=1024a header.b=xcfr3KVn; dkim-atps=neutral Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=linux-rtc-owner@vger.kernel.org; receiver=) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by bilbo.ozlabs.org (Postfix) with ESMTP id 4JVnNQ23XGz9tjx for ; Sat, 8 Jan 2022 02:35:18 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239655AbiAGPfQ (ORCPT ); Fri, 7 Jan 2022 10:35:16 -0500 Received: from mx-out.tlen.pl ([193.222.135.175]:44149 "EHLO mx-out.tlen.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239606AbiAGPfP (ORCPT ); Fri, 7 Jan 2022 10:35:15 -0500 Received: (wp-smtpd smtp.tlen.pl 5873 invoked from network); 7 Jan 2022 16:35:13 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=o2.pl; s=1024a; t=1641569713; bh=twRNu/a9b9RNQJ2jdkhVBvobmGSZZg0vR5jFe0bYAAw=; h=From:To:Cc:Subject; b=xcfr3KVn915DT0ov1MQokXBEF0mRuhAvp4zIOIvBNAwZuYn0yrR/nYBOHELoM0mhS rAUDGS/K2gJ5d/vt0KtZI0vCLXK5r97jKZAKjQjYLFkLHq9ZbBVIDnq8KO3gsPD1Gn zm/nqgatRwikkYgklB90/rTBS5DUr/ralQSDVsDw= Received: from aafo3.neoplus.adsl.tpnet.pl (HELO localhost.localdomain) (mat.jonczyk@o2.pl@[83.4.144.3]) (envelope-sender ) by smtp.tlen.pl (WP-SMTPD) with SMTP for ; 7 Jan 2022 16:35:13 +0100 From: =?utf-8?q?Mateusz_Jo=C5=84czyk?= To: linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org Cc: =?utf-8?q?Mateusz_Jo=C5=84czyk?= , Alessandro Zummo , Alexandre Belloni Subject: [PATCH] RFC: rtc-mc146818-lib: wait longer for UIP to clear Date: Fri, 7 Jan 2022 16:34:54 +0100 Message-Id: <20220107153454.391708-1-mat.jonczyk@o2.pl> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 X-WP-MailID: 3439be24a1bcffc31e6316b4f92dcfc7 X-WP-AV: skaner antywirusowy Poczty o2 X-WP-SPAM: NO 0000000 [gVMU] Precedence: bulk List-ID: X-Mailing-List: linux-rtc@vger.kernel.org Before reading date / time from the CMOS RTC, we wait for the UIP (Update in progress) bit to clear --- so that the values are correct and consistent. To avoid a hang, there is a time limit after which we give up waiting. Increase the time limit from 10 to 20ms in case there are RTCs out there that are much slower than expected. This is to be applied on top of rtc-next. Note: This may cause problems with hpet_rtc_interrupt() if the CMOS RTC breaks down while the system is running and RTC update interrupt / RTC alarm interrupt happens to be enabled (which should be rare). hpet_rtc_interrupt() is executed usually 64 times per second and after this patch it may take up to 20ms to complete - which may constantly occupy one CPU. This looks very unlikely, though. So, I don't know whether implementing this change is worth it and even if 20ms is enough. So I'm asking for opinions. This comment from Mr Alexandre Belloni got me thinking and is why I consider this patch: > We'll probably get some breakage later on because many RTCs using this > driver are not adhering to the spec. (See: https://lore.kernel.org/linux-rtc/277177e7-46a0-522c-297c-ad3ee0c15793@o2.pl/T/ ) Signed-off-by: Mateusz Jończyk Cc: Alessandro Zummo Cc: Alexandre Belloni Fixes: ec5895c0f2d8 ("rtc: mc146818-lib: extract mc146818_avoid_UIP") --- drivers/rtc/rtc-mc146818-lib.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c index f62e658cbe23..55e7d2a7578a 100644 --- a/drivers/rtc/rtc-mc146818-lib.c +++ b/drivers/rtc/rtc-mc146818-lib.c @@ -21,7 +21,7 @@ bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param), unsigned long flags; unsigned char seconds; - for (i = 0; i < 10; i++) { + for (i = 0; i < 20; i++) { spin_lock_irqsave(&rtc_lock, flags); /* @@ -79,8 +79,8 @@ bool mc146818_avoid_UIP(void (*callback)(unsigned char seconds, void *param), EXPORT_SYMBOL_GPL(mc146818_avoid_UIP); /* - * If the UIP (Update-in-progress) bit of the RTC is set for more then - * 10ms, the RTC is apparently broken or not present. + * If the UIP (Update-in-progress) bit of the RTC is set for more than + * 20ms, the RTC is apparently broken or not present. */ bool mc146818_does_rtc_work(void) {