linux-kernel - Re: [PATCH] of: skip disabled CPU nodes

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Date:   Wed, 26 Aug 2020 08:01:49 -0500
From:   Frank Rowand <frowand.list@...il.com>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of: skip disabled CPU nodes

On 2020-08-26 07:02, Matthias Schiffer wrote:
> Allow disabling CPU nodes using status = "disabled".
> 
> This allows a bootloader to change the number of available CPUs (for
> example when a common DTS is used for SoC variants with different numbers
> of cores) without deleting the nodes altogether (which may require
> additional fixups where the CPU nodes are referenced, e.g. a cooling
> map).
> 
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> ---
>  drivers/of/base.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index ea44fea99813..d547e9deced1 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -796,6 +796,8 @@ struct device_node *of_get_next_cpu_node(struct device_node *prev)
>  		of_node_put(node);
>  	}
>  	for (; next; next = next->sibling) {
> +		if (!__of_device_is_available(next))
> +			continue;
>  		if (!(of_node_name_eq(next, "cpu") ||
>  		      __of_node_is_type(next, "cpu")))
>  			continue;
> 

The original implementation of of_get_next_cpu_node() had
that check, but status disabled for cpu nodes has different
semantics than other nodes, and the check broke some systems.
The check was removed by c961cb3be906 "of: Fix cpu node
iterator to not ignore disabled cpu nodes".

It would be useful to document that difference in the
header comment of of_get_next_cpu_node().

-Frank