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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,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 371D1C388F9 for ; Thu, 22 Oct 2020 14:31:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D07CF2463B for ; Thu, 22 Oct 2020 14:31:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S368176AbgJVObI (ORCPT ); Thu, 22 Oct 2020 10:31:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:48308 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S368175AbgJVObI (ORCPT ); Thu, 22 Oct 2020 10:31:08 -0400 Received: from gaia (unknown [95.145.162.19]) (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 6751524171; Thu, 22 Oct 2020 14:31:05 +0000 (UTC) Date: Thu, 22 Oct 2020 15:31:02 +0100 From: Catalin Marinas To: Greg Kroah-Hartman Cc: Qais Yousef , Will Deacon , Marc Zyngier , "Peter Zijlstra (Intel)" , Morten Rasmussen , 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: <20201022143102.GH1229@gaia> 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> <20201022134752.wtcdkbi4fjn2blh6@e107158-lin> <20201022135559.GB1788090@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201022135559.GB1788090@kroah.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Thu, Oct 22, 2020 at 03:55:59PM +0200, Greg Kroah-Hartman wrote: > On Thu, Oct 22, 2020 at 02:47:52PM +0100, Qais Yousef wrote: > > On 10/21/20 15:41, Will Deacon wrote: > > > > We already expose MIDR and REVIDR via the current sysfs interface. We > > > > can expand it to include _all_ the other ID_* regs currently available > > > > to user via the MRS emulation and we won't have to debate what a new > > > > interface would look like. The MRS emulation and the sysfs info should > > > > probably match, though that means we need to expose the > > > > ID_AA64PFR0_EL1.EL0 field which we currently don't. > > > > > > > > I do agree that an AArch32 cpumask is an easier option both from the > > > > kernel implementation perspective and from the application usability > > > > one, though not as easy as automatic task placement by the scheduler (my > > > > first preference, followed by the id_* regs and the aarch32 mask, though > > > > not a strong preference for any). > > > > > > If a cpumask is easier to implement and easier to use, then I think that's > > > what we should do. It's also then dead easy to disable if necessary by > > > just returning 0. The only alternative I would prefer is not having to > > > expose this information altogether, but I'm not sure that figuring this > > > out from MIDR/REVIDR alone is reliable. > > > > So the mask idea is about adding a new > > > > /sys/devices/system/cpu/aarch32_cpus > > > > ? > > Is this a file, a directory, or what? What's the contents? > > Without any of that, I have no idea if it's "ok" or not... I don't know what Qais thinks but a file matching the syntax of the present/online/offline/possible files (e.g. 0-3) would look more consistent. -- Catalin