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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 12AD3C04FDF for ; Wed, 16 Aug 2023 15:05:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343955AbjHPPEa (ORCPT ); Wed, 16 Aug 2023 11:04:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52436 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343957AbjHPPD5 (ORCPT ); Wed, 16 Aug 2023 11:03:57 -0400 Received: from relay7-d.mail.gandi.net (relay7-d.mail.gandi.net [217.70.183.200]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B70532684; Wed, 16 Aug 2023 08:03:55 -0700 (PDT) Received: by mail.gandi.net (Postfix) with ESMTPSA id A64BE20003; Wed, 16 Aug 2023 15:03:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1692198234; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qH2B3kaqc6zMAtbHFvaHpCR6NMBsAraFbuMNrJUPJig=; b=RpxshUiAvUr9lcEJ4n9fSwHREhh9jijfqHo8BkUP8VoYSysXR6U6yalV06QG+HpbhzH5eS QG5dovTZorv2NrfyjgNhA6iXA5ciKgXlAhiWKn4zjtqoYPM3nEvEh+LjtGWEnlhjJSCkCY VKtNgcaQ+JnKRXN9B94AkHLdpb8fn81PVNUSXDXvsxC82JpZogaytFjUuON7H+FGz0pyJL cf5dcfb05sFkKjcXaLzqqCvJZe2ppffPKmD3Im4kCJv0FsYzcTAlOmFALU/NvEcvSNmkGG +f5fJClzPkGJk6F22H77Mx4+IQli8/QeQV3SNvSCIQ9TiE9Dp1mjAcn98sWNTg== Date: Wed, 16 Aug 2023 17:03:53 +0200 From: Alexandre Belloni To: Guenter Roeck Cc: Alessandro Zummo , Benson Leung , Miquel Raynal , Thomas Gleixner , John Stultz , Stephen Boyd , linux-rtc@vger.kernel.org, linux-kernel@vger.kernel.org, Brian Norris Subject: Re: [PATCH 0/7] rtc: Add support for limited alarm timer offsets Message-ID: <20230816150353137debc5@mail.local> References: <20230816133936.2150294-1-linux@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230816133936.2150294-1-linux@roeck-us.net> X-GND-Sasl: alexandre.belloni@bootlin.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On 16/08/2023 06:39:29-0700, Guenter Roeck wrote: > Some alarm timers are based on time offsets, not on absolute times. > In some situations, the amount of time that can be scheduled in the > future is limited. This may result in a refusal to suspend the system, > causing substantial battery drain. > > This problem was previously observed on a Chromebook using the cros_ec > rtc driver. EC variants on some older Chromebooks only support 24 hours > of alarm time in the future. To work around the problem on affected > Chromebooks, code to limit the maximum alarm time was added to the cros_ec > rtc driver with commit f27efee66370 ("rtc: cros-ec: Limit RTC alarm range > if needed"). The problem is now seen again on a system using the cmos > RTC driver on hardware limited to 24 hours of alarm time, so a more > generic solution is needed. > > Some RTC drivers remedy the situation by setting the alarm time to the > maximum supported time if a request for an out-of-range timeout is made. > This is not really desirable since it may result in unexpected early > wakeups. It would be even more undesirable to change the behavior > of existing widely used drivers such as the cmos RTC driver. > > The existing range_max variable in struct rtc_device can not be used > to determine the maximum time offset supported by an rtc chip since > it describes the maximum absolute time supported by the chip, not the > maximum time offset that can be set for alarms. > > To reduce the impact of this problem, introduce a new variable > rtc_time_offset in struct rtc_device to let RTC drivers report the maximum > supported alarm time offset. The code setting alarm timers can then > decide if it wants to reject setting alarm timers to a larger value, if it > wants to implement recurring alarms until the actually requested alarm > time is met, or if it wants to accept the limited alarm time. Use the new > variable to limit the alarm timer range. > > The series is intended to solve the problem with minimal changes in the > rtc core and in affected drivers. > > An alternative I had considered was to have the alarmtimer code guess the > maximum timeout supported by the rtc hardware. I discarded it as less > desirable since it had to retry repeatedly depending on rtc limitations. > This often resulted in error messages by the rtc driver. On top of that, > it was all but impossible to support rtc chips such as tps6586x which > can only support wake alarms up to 16,383 seconds in the future. > > The first patch of the series adds support for providing the maximum > supported time offset to the rtc core. The second patch uses that value > in the alarmtimer code to set the maximum wake-up time from system suspend. > Subsequent patches add support for reporting the maximum alarm timer offset > to a subset of affected drivers. > > Previous discussion: > https://lore.kernel.org/lkml/Y19AdIntJZGnBh%2Fy@google.com/T/#mc06d206d5bdb77c613712148818934b4f5640de5 > I'm fine with the series, however, this doesn't solve the issue for RTCs that have an absolute limit on the alarm (as opposed to an offset to the current time/date). > ---------------------------------------------------------------- > Guenter Roeck (7): > rtc: Add support for limited alarm timer offsets > rtc: alarmtimer: Use maximum alarm time offset > rtc: cros-ec: Detect and report supported alarm window size > rtc: cmos: Report supported alarm limit to rtc infrastructure > rtc: tps6586x: Report maximum alarm limit to rtc core > rtc: ds1305: Report maximum alarm limit to rtc core > rtc: rzn1: Report maximum alarm limit to rtc core > > drivers/rtc/rtc-cmos.c | 11 +++++++++++ > drivers/rtc/rtc-cros-ec.c | 38 +++++++++++++++++++++++--------------- > drivers/rtc/rtc-ds1305.c | 3 ++- > drivers/rtc/rtc-rzn1.c | 1 + > drivers/rtc/rtc-tps6586x.c | 1 + > include/linux/rtc.h | 1 + > kernel/time/alarmtimer.c | 13 +++++++++++++ > 7 files changed, 52 insertions(+), 16 deletions(-) -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com