From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754274Ab2LRCoZ (ORCPT ); Mon, 17 Dec 2012 21:44:25 -0500 Received: from mga02.intel.com ([134.134.136.20]:44021 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753989Ab2LRCoY (ORCPT ); Mon, 17 Dec 2012 21:44:24 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.84,305,1355126400"; d="scan'208";a="235397195" Date: Tue, 18 Dec 2012 10:44:48 +0800 From: Feng Tang To: Jason Gunthorpe Cc: John Stultz , Thomas Gleixner , Alessandro Zummo , linux-kernel@vger.kernel.org, alek.du@intel.com Subject: Re: [PATCH 1/3] timekeeping: Add persistent_clock_exist flag Message-ID: <20121218024448.GB6196@feng-snb> References: <50CA7EE4.3000306@linaro.org> <20121214013725.GA11276@feng-snb> <50CA8837.5010800@linaro.org> <20121214023826.GA31613@obsidianresearch.com> <20121214031330.GC11276@feng-snb> <20121214041024.GA1040@obsidianresearch.com> <50CB98AA.5090600@linaro.org> <20121214215651.GA31384@obsidianresearch.com> <20121217161433.GB4762@feng-snb> <20121217182202.GA10368@obsidianresearch.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121217182202.GA10368@obsidianresearch.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 17, 2012 at 11:22:02AM -0700, Jason Gunthorpe wrote: > On Tue, Dec 18, 2012 at 12:14:33AM +0800, Feng Tang wrote: > > > > Sure, but my view on this is that it has nothing to do with > > > read_persistent_clock. If the RTC driver can run with IRQs off is a > > > property of the RTC driver and RTC hardware - it has nothing to do > > > with the platform. ARM platforms will vary on a machine by machine > > > basis. The rtc-mv driver used on my ARM system is perfectly > > > re-entrant, lots of rtc on SOC drivers will be the same. > > > > > > If this is the only thing keeping you on read_persistent_clock, for > > > real RTCs, then how about a RTC_DEV_SAFE_READ flag (or whatever) in > > > rtc_device.flags? > > > > > > Reserve read_persistent_clock for things like that very specialized > > > non-RTC ARM counter. > > > > Yes, these non-RTC device is one reason for keeping read_persistent_clock, > > one other reason I can think of is the CONFIG_RTC_LIB is not always on by > > default for all Archs, and some platforms may chose to disable it on purpose. > > When CONFIG_RTC_LIB is not set, we need the read_persistent_clock for > > time init/suspend/resume. > > I thought your concern was the case where the RTC was turned on and > read_persistent_clock was also turned on. Having a flag in the RTC and > disabling read_persistent_clock for that situation would help you > avoid the double code path to the same hardware. No, it's not about my concern (actually I don't have concerns :), my 3 patches are just some optimization). My point is the "driver/rtc" or "drivers/rtc/class.c" can't be ganrateeded to be built for all kernels, myself saw several cases, under which the read_persistent_clock is still needed. If you want drivers/rtc code to take the priority, first thing you have to do is to make those codes always "obj-y=xxx.o" Thanks, Feng