From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756540Ab3AOIs2 (ORCPT ); Tue, 15 Jan 2013 03:48:28 -0500 Received: from mail-bk0-f48.google.com ([209.85.214.48]:62276 "EHLO mail-bk0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753565Ab3AOIs0 (ORCPT ); Tue, 15 Jan 2013 03:48:26 -0500 Date: Tue, 15 Jan 2013 08:48:21 +0000 From: Lee Jones To: Joe Perches Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, arnd@arndb.de, linus.walleij@stericsson.com, cbouatmailru@gmail.com, Jonas Aaberg Subject: Re: [PATCH 04/18] power: ab8500_fg: Replace msleep() with usleep_range() for greater accuracy Message-ID: <20130115084821.GT12385@gmail.com> References: <1357909986-9262-1-git-send-email-lee.jones@linaro.org> <1357909986-9262-5-git-send-email-lee.jones@linaro.org> <1358183857.19400.13.camel@joe-AO722> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1358183857.19400.13.camel@joe-AO722> 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, 14 Jan 2013, Joe Perches wrote: > On Fri, 2013-01-11 at 13:12 +0000, Lee Jones wrote: > > Doing so provides a greater degree of accuracy when dealing with > > time-frames between 1us and 20ms. msleep() is only accurate for > > wake-ups greater than 20ms. > [] > > diff --git a/drivers/power/ab8500_fg.c b/drivers/power/ab8500_fg.c > [] > > @@ -956,7 +956,7 @@ static int ab8500_fg_load_comp_volt_to_capacity(struct ab8500_fg *di) > > do { > > vbat += ab8500_fg_bat_voltage(di); > > i++; > > - msleep(5); > > + usleep_range(5000, 5001); > > If you're going to give a range that small > you might as well use usleep instead. > > Otherwise, add some tolerance to allow any > other coalesced wakeup to occur. I can't increase the tolerance, as I don't know how that would effect the running of the system, and the person who would know is off on parental leave. What I can tell you is we're only using usleep_range() because there is no usleep in the kernel. At least that's what we've been led to believe: Documentation/timers/timers-howto.txt: - Why is there no "usleep" / What is a good range? Since usleep_range is built on top of hrtimers, the wakeup will be very precise (ish), thus a simple usleep function would likely introduce a large number of undesired interrupts. -- Lee Jones Linaro ST-Ericsson Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog