From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755112AbZINIKR (ORCPT ); Mon, 14 Sep 2009 04:10:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753603AbZINIKQ (ORCPT ); Mon, 14 Sep 2009 04:10:16 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:56022 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753429AbZINIKP (ORCPT ); Mon, 14 Sep 2009 04:10:15 -0400 Date: Mon, 14 Sep 2009 09:10:01 +0100 From: Russell King - ARM Linux To: Jamie Lokier Cc: Marek Vasut , Felipe Contreras , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] arm: remove unused code in delay.S Message-ID: <20090914081001.GB14519@n2100.arm.linux.org.uk> References: <1252875960-21512-1-git-send-email-felipe.contreras@gmail.com> <200909132328.47079.marek.vasut@gmail.com> <20090913230008.GC30169@n2100.arm.linux.org.uk> <20090914002100.GD30621@shareable.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090914002100.GD30621@shareable.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 14, 2009 at 01:21:00AM +0100, Jamie Lokier wrote: > Russell King - ARM Linux wrote: > > On Sun, Sep 13, 2009 at 11:28:47PM +0200, Marek Vasut wrote: > > > > bhi __delay > > > > mov pc, lr > > > > ENDPROC(__udelay) > > > > > > > Hi > > > > > > why was this code there in the first place ? > > > > To make the delay loop more stable and predictable on older CPUs. > > So why has it been commented out, if it's needed for that? We moved on and it penalises later CPUs, leading to udelay providing shorter delays than requested. So the choice was either stable and predictable on older CPUs but buggy on newer CPUs, or correct on all CPUs but gives unnecessarily longer delays on older CPUs.