Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933771AbaJ2P0J (ORCPT ); Wed, 29 Oct 2014 11:26:09 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:36253 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932962AbaJ2P0H (ORCPT ); Wed, 29 Oct 2014 11:26:07 -0400 Date: Wed, 29 Oct 2014 08:25:02 -0700 From: Guenter Roeck To: Johan Hovold Cc: Russell King - ARM Linux , Andrew Morton , Felipe Balbi , Alessandro Zummo , Tony Lindgren , =?iso-8859-1?Q?Beno=EEt?= Cousson , Lokesh Vutla , nsekhar@ti.com, t-kristo@ti.com, j-keerthy@ti.com, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org, rtc-linux@googlegroups.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 00/20] rtc: omap: fixes and power-off feature Message-ID: <20141029152502.GA20565@roeck-us.net> References: <20141024195532.GF19377@localhost> <20141027162251.d7ff2a5f31917c638d4e47f7@linux-foundation.org> <20141028002552.GX12379@n2100.arm.linux.org.uk> <20141028081616.GL2006@localhost> <20141028084745.GY12379@n2100.arm.linux.org.uk> <20141028131257.GS2006@localhost> <20141028151610.GA12379@n2100.arm.linux.org.uk> <20141029123418.GB2265@localhost> <20141029131020.GB12379@n2100.arm.linux.org.uk> <20141029132244.GD2265@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141029132244.GD2265@localhost> User-Agent: Mutt/1.5.21 (2010-09-15) X-Authenticated_sender: guenter@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-CTCH-PVer: 0000001 X-CTCH-Spam: Unknown X-CTCH-VOD: Unknown X-CTCH-Flags: 0 X-CTCH-RefID: str=0001.0A02020A.5451070E.020B,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0 X-CTCH-Score: 0.000 X-CTCH-ScoreCust: 0.000 X-CTCH-Rules: C_4847, X-CTCH-SenderID: linux@roeck-us.net X-CTCH-SenderID-Flags: 0 X-CTCH-SenderID-TotalMessages: 16 X-CTCH-SenderID-TotalSpam: 0 X-CTCH-SenderID-TotalSuspected: 0 X-CTCH-SenderID-TotalConfirmed: 0 X-CTCH-SenderID-TotalBulk: 0 X-CTCH-SenderID-TotalVirus: 0 X-CTCH-SenderID-TotalRecipients: 0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: mailgid no entry from get_relayhosts_entry X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 29, 2014 at 02:22:44PM +0100, Johan Hovold wrote: > On Wed, Oct 29, 2014 at 01:10:20PM +0000, Russell King - ARM Linux wrote: > > On Wed, Oct 29, 2014 at 01:34:18PM +0100, Johan Hovold wrote: > > > On Tue, Oct 28, 2014 at 03:16:10PM +0000, Russell King - ARM Linux wrote: > > > > And how is that different from having a set of power-off handlers, and > > > > reporting when each individual one fails? Don't you want to know if > > > > your primary high priority reboot handler fails, just as much as you > > > > want to know if your final last-resort power-off handler fails? > > > > > > Good point. Failed power-off should probably be logged by the power-off > > > call chain implementation (which seems to makes notifier chains a bad > > > fit). > > > > > > And what about any power-off latencies? Should this always be dealt with > > > in the power-off handler? > > > > > > Again, if it's predictable and high, as in the OMAP RTC case, it should > > > go in the handler. But what if it's just normal bus latencies > > > (peripheral busses, i2c, or whatever people may come up with)? > > > > > > Should there always be a short delay before calling the next handler? > > > > If the handler has determined that it has failed, then why delay before > > trying the next handler? At the point it has decided it has failed, > > surely that's after it has waited sufficient time to determine that > > failure? > > The current handlers we have are not expecting any other handler to be > run after they return. My question was whether all these handlers should > get a short mdelay added to them (e.g. to compensate for bus latencies) Some of them do add a delay. > or if this could be done in the power-off handler (e.g. before printing > the error message). > That might make sense, but it would have to be configurable, since the delay is platform specific and power-off handler does not know how long to wait (the longest delay I have seen is 10 seconds). > > > > Or different from having no power-off handlers. > > > > > > That is actually quite different, as in that case we call machine_halt > > > instead (via kernel_halt). > > > > Today, ARM does exactly what x86 does. If there's no power off handler > > registered, machine_power_off() shuts down other CPUs and returns. > > No, if there are no power-off handlers registered, kernel/reboot.c will > never call machine_power_off: > > /* Instead of trying to make the power_off code look like > * halt when pm_power_off is not set do it the easy way. > */ > if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off) > cmd = LINUX_REBOOT_CMD_HALT; > > So in that case on arm, a system-halted message is printed, and we never > return to user-space. > Some architectures do that, or go into an endless loop. Others do return from machine_power_off. Having a well defined behavior would be nice (such as dumping an error mesasge and calling machine_halt if machine_power_off returns). Only question would be where to put it. kernel_power_off() might be a good place; only problem is that there are direct callers of machine_power_off(). Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/