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 780F5EEAA40 for ; Thu, 14 Sep 2023 14:07:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239455AbjINOHc (ORCPT ); Thu, 14 Sep 2023 10:07:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59422 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234873AbjINOHc (ORCPT ); Thu, 14 Sep 2023 10:07:32 -0400 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 44DDD1BF8; Thu, 14 Sep 2023 07:07:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=GIdT/cJmFA2qx50pgPlJRNzy/bheI4vUqGYQu+a7PMI=; b=raixHrVeNVHHMS+SmMW0fsVxI+ rZLO2b1FApnkXyJLVlkjBZUzsfFxmDi2JMVVu/R8wleWSzTAHzOFKzQL/zWb/JJhTJQkeyGGl2H3d 1EsUw8fAPKHCZzu4CyyEqx+rG9yuFwm7T+vos+z7VLqGttytZaDieHznwmb3696A6aPLvSAslWr7a thmdyxIrHQUHf4/fW3Cr1tTqOrfips0KHORhG+5wXWbJd9QGypzhjjzPeg+uOfhgIbBdTkF3z9ckY NUhze25dfC5TxiZv0q43BsedV3/l/zOQC9B/nOQb7gFNThJ/nZ0J8fzai0g8EC7sBDROC7wVMPZBJ p/hgjtbQ==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:37510) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1qgn08-0004Jo-2O; Thu, 14 Sep 2023 15:07:24 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1qgn06-0004ol-Vs; Thu, 14 Sep 2023 15:07:22 +0100 Date: Thu, 14 Sep 2023 15:07:22 +0100 From: "Russell King (Oracle)" To: Jonathan Cameron Cc: James Morse , linux-pm@vger.kernel.org, loongarch@lists.linux.dev, linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, kvmarm@lists.linux.dev, x86@kernel.org, Salil Mehta , Jean-Philippe Brucker , jianyong.wu@arm.com, justin.he@arm.com Subject: Re: [RFC PATCH v2 06/35] arm64: setup: Switch over to GENERIC_CPU_DEVICES using arch_register_cpu() Message-ID: References: <20230913163823.7880-1-james.morse@arm.com> <20230913163823.7880-7-james.morse@arm.com> <20230914122715.000076be@Huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230914122715.000076be@Huawei.com> Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org 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! -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!