From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27022C433EF for ; Fri, 29 Oct 2021 10:10:56 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D761B610E5 for ; Fri, 29 Oct 2021 10:10:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org D761B610E5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To: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-Owner; bh=Ixpg5t0DOUXtN19njPEmjR549cKhKV+znqJXNBhwD7s=; b=isQpgGYJP5GAcH 1JB6rlZilggSTCagSpNoSR2oCnHqtUhCZHSoH1bg9fQZVJwcmwUz5z6ylLeJ5U9CRbgy1afrWHSpM WmhEyVQToh7MwEL5H3I9PYe8bdQyakECNhkxXxmL0y7I0sT2fPW1GJfbcsgtejfwJ37Ch+bL9XU+S 9oLKyT9WtJLo1hJZV1aiIUWUr4iwnIPHgzkjrVwvhGJBN5U/lAQHdU1NwzjehpRgaXsLVlJR13dj7 8rgmHxvb2ALLJsu7xeTZbZ7cpLSlxQSWf0mwp2azB3Zj7It6WKB3AKPTF3YZAfOCcbqUi9OfWIQkO Ntq62W1TRON7I8ffNQMg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mgOpI-00AYx0-4Y; Fri, 29 Oct 2021 10:09:32 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mgOpD-00AYwN-JS for linux-arm-kernel@lists.infradead.org; Fri, 29 Oct 2021 10:09:29 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id BFF2361186; Fri, 29 Oct 2021 10:09:26 +0000 (UTC) Date: Fri, 29 Oct 2021 11:09:23 +0100 From: Catalin Marinas To: Joakim Tjernlund Cc: "linux-arm-kernel@lists.infradead.org" Subject: Re: Running/building an 32 bits kernel on A53 CPU? Message-ID: References: <2eca38941fefa6cc57cb2d8a547cf42c25af197f.camel@infinera.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <2eca38941fefa6cc57cb2d8a547cf42c25af197f.camel@infinera.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211029_030927_685926_80C482B2 X-CRM114-Status: GOOD ( 12.00 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Oct 29, 2021 at 08:27:35AM +0000, Joakim Tjernlund wrote: > In order to reduce RAM usage we are wondering if running an 32 bits > kernel on ARM A53 CPU is a good idea? No. Really. What's the RAM size on your SoC? > Is it possible to build such a kernel? If so, how to go about it? > Should one use ARCH=arm and a 32 bits toolchain or > ARCH=arm64 and 64 bits toolchain and adding 32 bits compile options? If you want a 32-bit kernel, you'd have to use ARCH=arm and a 32-bit toolchain. This would give you an ARMv7 kernel that can run on ARMv8 hardware. But you'd miss errata workarounds for example and any other features that come with ARMv8. I don't recommend this at all. If you have some specific embedded system, you can disable kernel features you don't need to make it smaller. Also note that you can still run 32-bit applications with a 64-bit kernel. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel