Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753540Ab2E2KT0 (ORCPT ); Tue, 29 May 2012 06:19:26 -0400 Received: from casper.infradead.org ([85.118.1.10]:52991 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753170Ab2E2KTZ (ORCPT ); Tue, 29 May 2012 06:19:25 -0400 Message-ID: <1338286760.11518.162.camel@shinybook.infradead.org> Subject: Re: [PATCH] mtd: dc21285.c: remove double check of CONFIG_ARCH_NETWINDER From: David Woodhouse To: Christian Dietrich Cc: Artem Bityutskiy , Dmitry Eremin-Solenikov , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org, vamos-dev@lists.cs.fau.de Date: Tue, 29 May 2012 11:19:20 +0100 In-Reply-To: <20120529100646.GA23383@faui49q.informatik.uni-erlangen.de> References: <1338040464.2525.38.camel@koala> <20120525082812.GA12238@faui49q.informatik.uni-erlangen.de> <20120529100646.GA23383@faui49q.informatik.uni-erlangen.de> Content-Type: multipart/signed; micalg="sha1"; protocol="application/x-pkcs7-signature"; boundary="=-x9/6MZ9QqEVn4VVOe1Vt" X-Mailer: Evolution 3.2.3 (3.2.3-3.fc16) Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9898 Lines: 155 --=-x9/6MZ9QqEVn4VVOe1Vt Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2012-05-29 at 12:06 +0200, Christian Dietrich wrote: > When CONFIG_ARCH_NETWINDER is unset nw_en_write is a NOP. But > machine_is_netwinder() also checks for > CONFIG_ARCH_NETWINDER. Therefore in the !netwinder case the > preprocessed code is: >=20 > if (0) > do {} while(0);=20 It's not a double check. It's a compile time check for "do we even need to build this code at all?", and a separate run time check for "do we need to run this code now?". Think about the case where CONFIG_ARCH_NETWINDER is set, but you aren't actually running this kernel binary on a netwinder *today*. Yes, we might not support multi-platform kernels on ARM yet, but we are slowly getting there. This kind of change just makes that harder. And even if the machine_is_netwinder() "function" is *currently* a macro which is hard-coded to return one or zero, that just means that your change achieves nothing in the compiler output. It'll be silently optimised away, or not, as appropriate. --=20 dwmw2 --=-x9/6MZ9QqEVn4VVOe1Vt Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIUbjCCBjQw ggQcoAMCAQICAR4wDQYJKoZIhvcNAQEFBQAwfTELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0YXJ0 Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcxKTAn BgNVBAMTIFN0YXJ0Q29tIENlcnRpZmljYXRpb24gQXV0aG9yaXR5MB4XDTA3MTAyNDIxMDE1NVoX DTE3MTAyNDIxMDE1NVowgYwxCzAJBgNVBAYTAklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQuMSsw KQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0aWZpY2F0ZSBTaWduaW5nMTgwNgYDVQQDEy9TdGFy dENvbSBDbGFzcyAxIFByaW1hcnkgSW50ZXJtZWRpYXRlIENsaWVudCBDQTCCASIwDQYJKoZIhvcN AQEBBQADggEPADCCAQoCggEBAMcJg8zOLdgasSmkLhOrlr6KMoOMpohBllVHrdRvEg/q6r8jR+EK 75xCGhR8ToREoqe7zM9/UnC6TS2y9UKTpT1v7RSMzR0t6ndl0TWBuUr/UXBhPk+Kmy7bI4yW4urC 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