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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 143EBEEAA4F for ; Thu, 14 Sep 2023 14:56:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240480AbjINO4k (ORCPT ); Thu, 14 Sep 2023 10:56:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234000AbjINO4j (ORCPT ); Thu, 14 Sep 2023 10:56:39 -0400 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A81E11FC4; Thu, 14 Sep 2023 07:56:35 -0700 (PDT) Received: from lhrpeml500005.china.huawei.com (unknown [172.18.147.201]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4RmgP90gY1z67Q1Y; Thu, 14 Sep 2023 22:55:57 +0800 (CST) Received: from localhost (10.202.227.76) by lhrpeml500005.china.huawei.com (7.191.163.240) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.31; Thu, 14 Sep 2023 15:56:33 +0100 Date: Thu, 14 Sep 2023 15:56:32 +0100 From: Jonathan Cameron To: "Russell King (Oracle)" CC: James Morse , , , , , , , , , , Salil Mehta , Jean-Philippe Brucker , , Subject: Re: [RFC PATCH v2 06/35] arm64: setup: Switch over to GENERIC_CPU_DEVICES using arch_register_cpu() Message-ID: <20230914155632.00003ca9@Huawei.com> In-Reply-To: References: <20230913163823.7880-1-james.morse@arm.com> <20230913163823.7880-7-james.morse@arm.com> <20230914122715.000076be@Huawei.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.227.76] X-ClientProxiedBy: lhrpeml100005.china.huawei.com (7.191.160.25) To lhrpeml500005.china.huawei.com (7.191.163.240) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Thu, 14 Sep 2023 15:07:22 +0100 "Russell King (Oracle)" wrote: > On Thu, Sep 14, 2023 at 12:27:15PM +0100, Jonathan Cameron wrote: > > On Wed, 13 Sep 2023 16:37:54 +0000 > > James Morse wrote: > > > > > To allow ACPI's _STA value to hide CPUs that are present, but not > > > available to online right now due to VMM or firmware policy, the > > > register_cpu() call needs to be made by the ACPI machinery when ACPI > > > is in use. This allows it to hide CPUs that are unavailable from sysfs. > > > > > > Switching to GENERIC_CPU_DEVICES is an intermediate step to allow all > > > five ACPI architectures to be modified at once. > > > > > > Switch over to GENERIC_CPU_DEVICES, and provide an arch_register_cpu() > > > that populates the hotpluggable flag. arch_register_cpu() is also the > > > interface the ACPI machinery expects. > > > > > > The struct cpu in struct cpuinfo_arm64 is never used directly, remove > > > it to use the one GENERIC_CPU_DEVICES provides. > > > > > > This changes the CPUs visible in sysfs from possible to present, but > > > on arm64 smp_prepare_cpus() ensures these are the same. > > > > > > Signed-off-by: James Morse > > > > After this the earlier question about ordering of cpu_dev_init() > > and node_dev_init() is relevant. > > > > Why won't node_dev_init() call > > get_cpu_devce() which queries per_cpu(cpu_sys_devices) > > and get NULL as we haven't yet filled that in? > > > > Or does it do so but that doesn't matter as well create the > > relevant links later? > > node_dev_init() will walk through the nodes calling register_one_node() > on each. This will trickle down to __register_one_node() which walks > all present CPUs, calling register_cpu_under_node() on each. > > register_cpu_under_node() will call get_cpu_device(cpu) for each and > will return NULL until the CPU is registered using register_cpu(), > which will now happen _after_ node_dev_init(). > > So, at this point, CPUs won't get registered, and initially one might > think that's a problem. > > However, register_cpu() will itself call register_cpu_under_node(), > where get_cpu_device() will return the now populated entry, and the > sysfs links will be created. > > So, I think what you've spotted is a potential chunk of code that > isn't necessary when using GENERIC_CPU_DEVICES after this change! > Makes sense thanks. I was just being too lazy to check and bouncing it back at James! *looks guilty* Jonathan