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[209.132.180.67]) by mx.google.com with ESMTP id j84-v6si6956970pfj.79.2018.06.22.02.25.27; Fri, 22 Jun 2018 02:26:11 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=fail header.i=@armlinux.org.uk header.s=pandora-2014 header.b=STdbxpQ6; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=armlinux.org.uk Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751624AbeFVJXi (ORCPT + 99 others); Fri, 22 Jun 2018 05:23:38 -0400 Received: from pandora.armlinux.org.uk ([78.32.30.218]:39186 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751235AbeFVJXg (ORCPT ); Fri, 22 Jun 2018 05:23:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2014; h=Sender:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=aHbubk1ywRvwkjiwlVwgUCWNTRXNHPTNOmD4iCImC2U=; b=STdbxpQ6PYInAvtfDnI6oqG+C lvT80hq6U9R3J+3q7E8HRqUYMDAzbhS+FAQpEMfEi5Jwv+XTqY10x6gvw/2t0SCvu6q4TsUUGRM+j wuzAgy2dMwWMF/G3Jnan1lHPCUuqkgoeDnlNzAK/jqzBdBP0roIwnvaO73x0rM5F2mSEU=; Received: from n2100.armlinux.org.uk ([2002:4e20:1eda:1:214:fdff:fe10:4f86]:37945) by pandora.armlinux.org.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.90_1) (envelope-from ) id 1fWIHk-0000hH-EH; Fri, 22 Jun 2018 10:23:16 +0100 Received: from linux by n2100.armlinux.org.uk with local (Exim 4.90_1) (envelope-from ) id 1fWIHd-0000qw-Tg; Fri, 22 Jun 2018 10:23:11 +0100 Date: Fri, 22 Jun 2018 10:23:05 +0100 From: Russell King - ARM Linux To: Geert Uytterhoeven Cc: Greg Ungerer , Chris Brandt , Nicolas Pitre , Arnd Bergmann , Vladimir Murzin , Simon Horman , Magnus Damm , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] [RFC] arm: Replace "multiple platforms" by "common platform" Message-ID: <20180622092305.GS17671@n2100.armlinux.org.uk> References: <20180621155906.12821-1-geert+renesas@glider.be> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180621155906.12821-1-geert+renesas@glider.be> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 21, 2018 at 05:59:06PM +0200, Geert Uytterhoeven wrote: > "ARM multiplatform" has actually two meanings: > ? 1. It groups platforms that follow the "ARM multiplatform" software > framework, > ? 2. It allows to build a single kernel that can be booted on multiple > ? ? ?platforms. > > Currently support for XIP and/or NOMMU cannot be enabled on platforms > that follow the "ARM multiplatform" framework, without duplicating their > machine selection logic under a new Kconfig symbol. As (in theory) all > platforms can be used with XIP and/or NOMMU, this is not sustainable. The reason for that has nothing to do with the way this option is named, and even after reading your commit message, I can't come up with any reason for this change other than "personally don't like the existing wording" which IMHO is not a good enough reason to randomly go around rewording stuff in the kernel. The reason that XIP and NOMMU can't be enabled with a multi-platform kernel is that there are often issues with different layouts of the physical memory space which can not be taken into account. Multi-platform works around that by (a) using the MMU to abstract away the differences on RAM, and (b) modifying the kernel text to adjust the virtual to physical translations. The latter is not possible with XIP, and the former should not be used with NOMMU. That means the kernel must be built to accomodate the physical layout on the target platform, and so building a kernel supporting multiple platforms with differing memory layouts makes no sense. This is exactly why I really don't like the idea of ARCH_MULTIPLATFORM being hijacked for NOMMU/XIP support. We've worked around the issues with "multi-platform" XIP/NOMMU by using things such as "ARM_SINGLE_V7M" to cover all V7M platforms (which must, by definition) have compatible physical layouts. Exactly the same approach should be adopted for other XIP/NOMMU platforms, and _not_ reusing ARCH_MULTIPLATFORM, which will lead to lots of non-bootable kernels. Another problems for NOMMU is that the kernel has to be linked for a specific _physical_ address. When you have ARCH_MULTIPLATFORM enabled, there is no facility to select that address. Sorry, but reusing ARCH_MULTIPLATFORM is really a non-starter and is confusing. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up According to speedtest.net: 8.21Mbps down 510kbps up