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 X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 03D85C4363A for ; Wed, 21 Oct 2020 20:26:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 93F1F24182 for ; Wed, 21 Oct 2020 20:26:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603311994; bh=knWpq9ayYtvYaJd6mEQADTiLp39WF7GfDQ1m3dk+0SE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=rF1DkCu2HvFYAzBrqRF193sum8OD4swnJT77DYK+Y17sdlpyGDWg3CFOH9jxnQEkT ODvwIq+GtnJ3V05Fssav2C1kW2B5cpebhS9gn3T+LvS3z+9U6gSZwi5HnxwqHhJXom 7j5UXG0O06Zu8ocZSW2tMHmwKhgjajNWn04UDdHg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2505295AbgJUU0e (ORCPT ); Wed, 21 Oct 2020 16:26:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:53072 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2505284AbgJUU0d (ORCPT ); Wed, 21 Oct 2020 16:26:33 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BD5F121D6C; Wed, 21 Oct 2020 20:26:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603311992; bh=knWpq9ayYtvYaJd6mEQADTiLp39WF7GfDQ1m3dk+0SE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=n/8uO/z30xFF1JPBo6UdIS+C5kgfgLhrdSDJeTwUqero71OOgSwlnALCTzNy3TNWH 5FeTPhwZdgcj/oI6eXgGXQiWwUFEz8BTWdDIVfQZ4OyRoRe685eFvvhtYkcK2GdEBn Z6yPeWKH/FYj+JIvBXV3YjjXH0/1rwNG/LRxGzKE= Date: Wed, 21 Oct 2020 21:26:27 +0100 From: Will Deacon To: Qais Yousef Cc: Catalin Marinas , Marc Zyngier , "Peter Zijlstra (Intel)" , Morten Rasmussen , Greg Kroah-Hartman , Linus Torvalds , James Morse , linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org Subject: Re: [RFC PATCH v2 4/4] arm64: Export id_aar64fpr0 via sysfs Message-ID: <20201021202626.GA18494@willie-the-truck> References: <20201021104611.2744565-1-qais.yousef@arm.com> <20201021104611.2744565-5-qais.yousef@arm.com> <63fead90e91e08a1b173792b06995765@kernel.org> <20201021121559.GB3976@gaia> <20201021144112.GA17912@willie-the-truck> <20201021150313.ecxawwxsowweye43@e107158-lin> <20201021152310.GA18071@willie-the-truck> <20201021160730.komcgrp7q2tly55w@e107158-lin> <20201021172345.GF18071@willie-the-truck> <20201021195736.mj4njbi6pxkbpbyf@e107158-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201021195736.mj4njbi6pxkbpbyf@e107158-lin> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Wed, Oct 21, 2020 at 08:57:36PM +0100, Qais Yousef wrote: > On 10/21/20 18:23, Will Deacon wrote: > > On Wed, Oct 21, 2020 at 05:07:30PM +0100, Qais Yousef wrote: > > > > > For example, the new sysctl_enable_asym_32bit could be a cpumask instead of > > > > > a bool as it currently is. Or we can make it a cmdline parameter too. > > > > > In both cases some admin (bootloader or init process) has to ensure to fill it > > > > > correctly for the target platform. The bootloader should be able to read the > > > > > registers to figure out the mask. So more weight to make it a cmdline param. > > > > > > > > I think this is adding complexity for the sake of it. I'm much more in > > > > > > I actually think it reduces complexity. No special ABI to generate the mask > > > from the kernel. The same opt-in flag is the cpumask too. > > > > Maybe I'm misunderstanding your proposal but having a cpumask instead of > > What I meant is that if we change the requirement to opt-in from a boolean > switch > > sysctl.enable_32bit_asym=1 > > to require the bootloader/init scripts provide the mask of aarch32 capable cpus > > sysctl.asym_32bit_cpus=0xf0 > > This will achieve multiple things at the same time: > > * Defer cpus specification to platform designers who want to > enable this feature on their platform. What do you mean by this? The kernel will obviously have to check that the mask is correct (i.e. it doesn't contain 64-bit only CPUs), at which point it's a boolean in disguise. > * We don't need a separate API to export which cpus are 32bit capable. > They can read it directly from /proc/sys/kernel/asym_32bit_cpus. > When it's 0 it means the system is not asymmetric. I don't see how this is better than a separate cpumask for this purpose. It feels like you're trying to overload the control and the identification, but that just makes things confusing and hard to use as I now need to know which logical CPUs correspond to which physical CPUs in order to set the command-line. > * If/when we want to disable this support in the future. The sysctl > handler will just have to return 0 all the time and ignore all > writes. It can do that as a boolean too, right? Will