Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752933AbZIOMXM (ORCPT ); Tue, 15 Sep 2009 08:23:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752178AbZIOMXL (ORCPT ); Tue, 15 Sep 2009 08:23:11 -0400 Received: from gateway-1237.mvista.com ([63.81.120.158]:3375 "EHLO gateway-1237.mvista.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750763AbZIOMXK (ORCPT ); Tue, 15 Sep 2009 08:23:10 -0400 Subject: Re: [PATCH] arm: remove unused code in delay.S From: Steve Chen To: Pavel Machek Cc: Felipe Contreras , Jamie Lokier , Russell King - ARM Linux , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Marek Vasut In-Reply-To: <20090915103739.GA19519@elf.ucw.cz> 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> <20090914081001.GB14519@n2100.arm.linux.org.uk> <94a0d4530909140558nd8d2c47lc9954563c80a574f@mail.gmail.com> <20090914140059.GC21580@n2100.arm.linux.org.uk> <94a0d4530909140738t7e4d646r134cfd884da21348@mail.gmail.com> <20090914144028.GG21580@n2100.arm.linux.org.uk> <94a0d4530909140814w36f7f5f0td2c25db07fbd4e57@mail.gmail.com> <20090915103739.GA19519@elf.ucw.cz> Content-Type: text/plain Date: Tue, 15 Sep 2009 07:29:21 -0500 Message-Id: <1253017761.3273.117.camel@linux-1lbu> Mime-Version: 1.0 X-Mailer: Evolution 2.22.1.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2397 Lines: 65 On Tue, 2009-09-15 at 12:37 +0200, Pavel Machek wrote: > > >> > Because then you get it whenever you configure for V4 as the lowest > > >> > denominator CPU, which leads to the buggy behaviour on better CPUs. > > >> > It's far better to leave it as is and just accept that the old CPUs > > >> > will have longer than necessary delays. If people really really > > >> > care (and there's likely to only be a small minority of them now) > > >> > changing the '0' to a '1' is a very simple change for them to carry > > >> > in their local tree. Unlike getting the right unrolling etc. > > >> > > >> Well, they can also 'git revert' this patch. If somebody really cares > > >> I think they should shout now and provide a better patch, otherwise > > >> this one should be merged. > > > > > > On the other hand, having the code there as it currently stands is not > > > harmful in any way, so leaving it there is just as easy. > > > > It makes the code less understandable. I'm not sure about linux's > > practices, but an #if 0 generally means somebody is being lazy. > > Not in this case, as you was explained to you. You may want to add > explaining comment above #if 0.... > Pavel Perhaps we can document with something like.. diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index aef63c8..ca8d535 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -813,6 +813,14 @@ config ARM_ERRATA_460075 ACTLR register. Note that setting specific bits in the ACTLR register may not be available in non-secure mode. +config OLD_CPU_DELAY + depends on CPU_32v3 || CPU_32v4 || CPU_32v4T + bool "Accurate delays for older CPU" + def_bool n + help + Enable if observing longer than expected delays and need more + accurate delays on older CPUs. + endmenu source "arch/arm/common/Kconfig" diff --git a/arch/arm/lib/delay.S b/arch/arm/lib/delay.S index 8d6a876..8b3fa63 100644 --- a/arch/arm/lib/delay.S +++ b/arch/arm/lib/delay.S @@ -42,7 +42,7 @@ ENTRY(__const_udelay) @ 0 <= r0 <= 0x7fffff06 @ Delay routine ENTRY(__delay) subs r0, r0, #1 -#if 0 +#if CONFIG_OLD_CPU_DELAY movls pc, lr subs r0, r0, #1 movls pc, lr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/