From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760005Ab3D3BLK (ORCPT ); Mon, 29 Apr 2013 21:11:10 -0400 Received: from mail-pa0-f45.google.com ([209.85.220.45]:62255 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758753Ab3D3BLG (ORCPT ); Mon, 29 Apr 2013 21:11:06 -0400 Message-ID: <517F1A27.3030206@linaro.org> Date: Mon, 29 Apr 2013 18:11:03 -0700 From: John Stultz User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Thomas Gleixner CC: LKML , Ingo Molnar , Magnus Damm Subject: Re: [patch 07/15] clocksource: Provide unbind interface in sysfs References: <20130425142452.908423538@linutronix.de> <20130425143435.964218245@linutronix.de> In-Reply-To: <20130425143435.964218245@linutronix.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/25/2013 01:31 PM, Thomas Gleixner wrote: > With the module refcount held for the current clocksource there is no > way to unload the module. > > Provide a sysfs interface which allows to unbind the clocksource. One > could argue that the clocksource override could be (ab)used to do so, > but the clocksource override cannot be used from the kernel itself, > while an unbind function can be used to programmatically check whether > a clocksource can be shutdown or not. > > The unbind functionality uses the new skip current feature of > clocksource_select and verifies that a fallback clocksource has been > installed. If the clocksource which should be unbound is the current > clocksource and no fallback can be found, unbind returns -EBUSY. > > This does not support the unbinding of a clocksource which is used as > the watchdog clocksource. No point in fostering crappy hardware. So.. if the clocksource you want to unbind is the highest rated continuous clocksource that doesn't need a watchdog (basically what's likely to be in-use and required to be unbinded), its likely to be selected as the watchdog already. ie: on a system that has only HPET/ACPI_PM, you can't unbind HPET, since its a watchdog. Or are you really wanting to prohibit this functionality for all CONFIG_CLOCKSOURCE_WATCHDOG hardware, which would be easier to do via build time ifdefs? thanks -john