From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756068Ab0ERHi7 (ORCPT ); Tue, 18 May 2010 03:38:59 -0400 Received: from www.tglx.de ([62.245.132.106]:50553 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753296Ab0ERHi5 (ORCPT ); Tue, 18 May 2010 03:38:57 -0400 Date: Tue, 18 May 2010 09:38:32 +0200 (CEST) From: Thomas Gleixner To: Feng Tang cc: Jacob Pan , "H. Peter Anvin" , Ingo Molnar , "Du, Alek" , Arjan van de Ven , LKML , John Stultz Subject: Re: [PATCH 7/8] x86/mrst: add vrtc driver which serves as a wall clock device In-Reply-To: <20100518142719.50ff74fa@feng-i7> Message-ID: References: <1273254108-3234-1-git-send-email-jacob.jun.pan@linux.intel.com> <1273254108-3234-8-git-send-email-jacob.jun.pan@linux.intel.com> <20100512103422.1d59cc85@feng-i7> <20100518142719.50ff74fa@feng-i7> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 18 May 2010, Feng Tang wrote: > Hi Thomas, > > > On Mon, 17 May 2010 17:15:55 +0800 > Thomas Gleixner wrote: > > > > > > > > Actually when to init the vrtc register is a big problem for me, > > > vrtc need be inited before timekeeping_init(), and I thought better > > > to put it somewhere in setup_arch(), as it is architecture > > > specific, and ioremap is not working at that time. Also that's the > > > reason I created a new wallclock_init func for x86_platforms, I > > > could not find a better way to do the vrtc init. > > > > There is no particular reason why we need to read it in > > timekeeping_init(). Nothing in the kernel needs the correct wall time > > at that point. So we can safely move the setting of xtime to rtc wall > > clock time to a separate timekeeping_late_init() function. > > > > John ??? > > > Yeah, good suggestion, if xtime init is moved to a later time in kernel > init flow, then vrtc's init function can be set a arch_initcall() John was away yesterday, so we have to wait for his answer, but I don't expect a nono from him. > > > > > + lock_cmos_prefix(reg); > > > > > > > > This lock_cmos magic should just die. I have no idea why > > > > something wants or wanted to access the RTC from an NMI. > > > > > > I will try to reuse the rtc_lock defined in rtc.c whose get/set_time > > > service won't be called with vrtc's at the same time. > > > > Please don't create artifical dependencies. Use a separate vrtc_lock > > to serialize the access to vrtc. > I just checked the code, when wall clock's get/set_time service is called, > it is always protected by rtc_lock(code in arch/x86/kernel/rtc.c), then > no need to add the lock for each individual register read/write operation. Grr. Yes, missed that the code is called under rtc_lock already. So you can drop the locking in your code completely. Thanks, tglx