linux-kernel - Re: [PATCH v4 16/20] arch_topology: Drop unnecessary check for uninitialised package

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Date:   Mon, 27 Jun 2022 14:12:52 +0100
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-kernel@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
        Atish Patra <atishp@...shpatra.org>,
        Atish Patra <atishp@...osinc.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Qing Wang <wangqing@...o.com>,
        Rob Herring <robh+dt@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Pierre Gondois <pierre.gondois@....com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 16/20] arch_topology: Drop unnecessary check for
 uninitialised package_id

On Tuesday 21 Jun 2022 at 20:20:30 (+0100), Sudeep Holla wrote:
> With the support of socket node parsing from the device tree and
> assigning 0 as package_id in absence of socket nodes, there is no need
> to check for invalid package_id. It is always initialised to 0 or values
> from the device tree socket nodes.
> 
> Just drop that now redundant check for uninitialised package_id.
> 
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  drivers/base/arch_topology.c | 11 -----------
>  1 file changed, 11 deletions(-)
> 
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 46fa1b70b02b..42448a5a9412 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -611,7 +611,6 @@ static int __init parse_dt_topology(void)
>  {
>  	struct device_node *cn, *map;
>  	int ret = 0;
> -	int cpu;
>  
>  	cn = of_find_node_by_path("/cpus");
>  	if (!cn) {
> @@ -633,16 +632,6 @@ static int __init parse_dt_topology(void)
>  
>  	topology_normalize_cpu_scale();
>  
> -	/*
> -	 * Check that all cores are in the topology; the SMP code will
> -	 * only mark cores described in the DT as possible.
> -	 */
> -	for_each_possible_cpu(cpu)
> -		if (cpu_topology[cpu].package_id < 0) {
> -			ret = -EINVAL;
> -			break;
> -		}
> -

Maybe it would still be good to keep this for systems with potential
errors in DT, where one forgets to add a core in cpu-map.

For example, if I modify juno.dts as follows:

--- a/arch/arm64/boot/dts/arm/juno.dts
+++ b/arch/arm64/boot/dts/arm/juno.dts
@@ -51,12 +51,9 @@ core0 {
                                        cpu = <&A53_0>;
                                };
                                core1 {
-                                       cpu = <&A53_1>;
-                               };
-                               core2 {
                                        cpu = <&A53_2>;
                                };
-                               core3 {
+                               core2 {
                                        cpu = <&A53_3>;
                                };
                        };

and miss a little core in cluster1, I would end up with an incomplete
topology: core3 would have cluster_id as -1, while all other CPUs would
have a valid value; also, core3 would have package_id = -1.

Thanks,
Ionela.

>  out_map:
>  	of_node_put(map);
>  out:
> -- 
> 2.36.1
>