From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754349Ab2GQJPm (ORCPT ); Tue, 17 Jul 2012 05:15:42 -0400 Received: from moutng.kundenserver.de ([212.227.17.10]:64448 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753767Ab2GQJPh (ORCPT ); Tue, 17 Jul 2012 05:15:37 -0400 From: Arnd Bergmann To: Christoph Hellwig Subject: Re: [PATCH 00/36] AArch64 Linux kernel port Date: Tue, 17 Jul 2012 08:07:24 +0000 User-Agent: KMail/1.12.2 (Linux/3.5.0-rc1+; KDE/4.3.2; x86_64; ; ) Cc: Catalin Marinas , Pavel Machek , Ingo Molnar , Olof Johansson , "linux-kernel@vger.kernel.org" , Linus Torvalds , Russell King , Andrew Morton , Alan Cox References: <1341608777-12982-1-git-send-email-catalin.marinas@arm.com> <201207151943.08183.arnd@arndb.de> <20120717065338.GA24699@infradead.org> In-Reply-To: <20120717065338.GA24699@infradead.org> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201207170807.25139.arnd@arndb.de> X-Provags-ID: V02:K0:X9YaJuy9JkRNO26DFdCDwW3dnyDzYyDSW8ZUl6jSDOH ZpFuBcqT4Am/nWvq7YmbmsJ7j4eiIHBC9Jkj6GX4olnZRhtBm8 SJq5S/jZblVYNOAPCmoRK1EP7S3/n5PSQGL91u8mXh7m44hzdT WsdfaL9jOsaunL2LNcMC6vPRhmoN8BfWanGzz5s2gGS2YEsEo5 EQ8RMjYtELN5hDXoz82t0Ea1J5qEkzLRvf7H5RgPwzeFOonopl A75gI69lUYarm82TndJQG+8EOuyVmWebI7bzLRXLaIdEtHiM0v xlSapAbonpvl9hcoapjd2nrtXCQLQEi75rlTrfmWJBYDcRYeqC 3xmnlY4Fw2U/AUs+6xqY= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday 17 July 2012, Christoph Hellwig wrote: > On Sun, Jul 15, 2012 at 07:43:07PM +0000, Arnd Bergmann wrote: > > Yes, I agree that's the best way to handle this. Compared to other > > architectures, I think x86 is the only that allows booting either a > > 32 or 64 bit kernel on the same system. We used to support 32 bit > > kernels on 64 bit PowerMac, but nobody used it and we discontinued > > it long ago. Tile 64 bit is actually incompatible with 32 bit kernels > > at the architecture level and would require a third mode. On sparc, > > parisc and mips, AFAIK we could support 32 bit kernels on 64 bit > > machines, but never did. > > On mips it works just fine. On Sparc I don't think Linux ever did it, > but Solaris did for a long time, as did (IIRC) NetBSD/OpenBSD. Ah, I didn't know about mips doing that. I also just remembered that s390 supports running 31 bit kernels on all 64 bit machines, but there is no longer official support for that from IBM's side AFAIK. I certainly expect ARM to be similar to powperpc and sparc here, and anyone trying to submit a 32 bit kernel port for a 64 bit platform will have a hard time arguing why that should be accepted into mainline. Arnd