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 1DFC9C433EF for ; Tue, 2 Nov 2021 15:45:55 +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 DECD460F5A for ; Tue, 2 Nov 2021 15:45:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org DECD460F5A 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=sj0GlZGukk8NQWikIgLE3wHtASAkqS9GlH2Q+FnY2UA=; b=N9PxixMXaJ9dyL Ql75JuGIJ8JQGJiSv9m9SwHJhMrum0ghjIp1dO4QWPfVc4SsLm2EV/DJEkOIKDvYsTQJI0xcseCKZ wAsLck0pFCqqy31n99YQsZW0y3k8++qXGokRQ5fhGBpRYTu41s67UlAjwe51W642G61zHTEElM7R4 ad7r6auE8GAY/km4LFtLf9RCXknmydAGWVYeDXjXrah+l3f74NaK+6hu+hhczWn76vWQmDQijt5bB Pjrb9uNGZ00oDbqO3ep+306ACVy5ReGWUIt8UqbOfDT05AkOuXadPcV0hSjuXi271NuyVzbFKngYj yRGn4S7gtTFd80e9APyw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mhvxf-002Ak3-Rk; Tue, 02 Nov 2021 15:44:31 +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 1mhvxc-002AjN-03 for linux-arm-kernel@lists.infradead.org; Tue, 02 Nov 2021 15:44:29 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4DA3F604AC; Tue, 2 Nov 2021 15:44:26 +0000 (UTC) Date: Tue, 2 Nov 2021 15:44:22 +0000 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> <033841d23095689c82a8c58d1d1f84f555e37a01.camel@infinera.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211102_084428_080365_A8A47EDD X-CRM114-Status: GOOD ( 22.58 ) 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 Tue, Nov 02, 2021 at 01:20:22PM +0000, Joakim Tjernlund wrote: > On Fri, 2021-10-29 at 10:32 +0000, Joakim Tjernlund wrote: > > On Fri, 2021-10-29 at 11:09 +0100, Catalin Marinas wrote: > > > 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? > > > > 32MB + 4MB SRAM > > > > > > > > > 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. > > Anything else you can think of why 32 bits kernel is a bad idea? 32-bit kernels on arm64 hardware are not "officially" supported by the maintainers (though there are some commercial deployments). Given the amount of RAM, you might as well give 32-bit uClinux a try ;) (even less tested). > I do wonder why 64 bits A53 enforces SMP? I only have one core in my > HW(custom ASIC) We removed it because we were not aware of any such UP system. Note that even with CONFIG_SMP enabled, the kernel still runs fine on a UP system. I guess you want to get rid of extra code in the final image. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel