linux-kernel - Re: [PATCH] cpu-topology: Skip the exist but not possible cpu nodes

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Date:   Mon, 6 Jan 2020 19:42:06 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Zeng Tao <prime.zeng@...ilicon.com>, sudeep.holla@....com
Cc:     linuxarm@...wei.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpu-topology: Skip the exist but not possible cpu nodes

On 02/01/2020 04:24, Zeng Tao wrote:
> When CONFIG_NR_CPUS is smaller than the cpu nodes defined in the device
> tree, the cpu node parsing will fail. And this is not reasonable for a
> legal device tree configs.
> In this patch, skip such cpu nodes rather than return an error.

Is this extra code really necessary?

Currently you get warnings indicating that CONFIG_NR_CPUS is too small
so you could correct the setup issue easily.

Example: Arm64 Juno board

$ grep "cpu@" ./arch/arm64/boot/dts/arm/juno.dts
		A57_0: cpu@0 {
		A57_1: cpu@1 {
		A53_0: cpu@100 {
		A53_1: cpu@101 {
		A53_2: cpu@102 {
		A53_3: cpu@103 {

root@...o:~# uname -r
5.5.0-rc5

root@...o:~# zcat /proc/config.gz | grep CONFIG_NR_CPUS
CONFIG_NR_CPUS=4

root@...o:~# cat /proc/cpuinfo | grep ^proc
processor       : 0
processor       : 1
processor       : 2
processor       : 3

root@...o:~# dmesg | grep "Unable\|Can't"
[    0.085089] Unable to find CPU node for /cpus/cpu@102
[    0.090179] /cpus/cpu-map/cluster1/core2: Can't get CPU for leaf core

[...]