linux-kernel - Re: [PATCH v2] of: base: Skip CPU nodes with "fail"/"fail-..." status

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Date:   Tue, 23 Nov 2021 00:42:02 -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 v2] of: base: Skip CPU nodes with "fail"/"fail-..." status

On 11/22/21 6:45 AM, Matthias Schiffer wrote:
> Allow fully disabling CPU nodes using status = "fail".
> 
> 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 could require
> additional fixups to avoid dangling phandle references.
> 
> Unknown status values (everything that is not "okay"/"ok", "disabled" or
> "fail"/"fail-...") will continue to be interpreted like "disabled",
> meaning that the CPU can be enabled during boot.
> 

Thank you for including all the references!  I find them helpful.

> References:
> - https://www.lkml.org/lkml/2020/8/26/1237

That reference should be:
  https://lore.kernel.org/all/CAL_Jsq+1LsTBdVaODVfmB0eme2jMpNL4VgKk-OM7rQWyyF0Jbw@mail.gmail.com/

Rob might be willing to fix that himself without a new patch version.

> - https://www.spinics.net/lists/devicetree-spec/msg01007.html

The following reference is the pull request for the devicetree specification
change that is provided in the previous reference.  I wouldn't include this
in the commit, but maybe Rob will.

> - https://github.com/devicetree-org/dt-schema/pull/61
> 
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> ---
> 
> v2: Treat unknown status values like "disabled", not like "fail"
> 
> 
>  drivers/of/base.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 61de453b885c..5b907600f5b0 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -650,6 +650,28 @@ bool of_device_is_available(const struct device_node *device)
>  }
>  EXPORT_SYMBOL(of_device_is_available);
>  
> +/**
> + *  __of_device_is_fail - check if a device has status "fail" or "fail-..."
> + *
> + *  @device: Node to check status for, with locks already held
> + *
> + *  Return: True if the status property is set to "fail" or "fail-..." (for any
> + *  error code suffix), false otherwise
> + */
> +static bool __of_device_is_fail(const struct device_node *device)
> +{
> +	const char *status;
> +
> +	if (!device)
> +		return false;
> +
> +	status = __of_get_property(device, "status", NULL);
> +	if (status == NULL)
> +		return false;
> +
> +	return !strcmp(status, "fail") || !strncmp(status, "fail-", 5);
> +}
> +
>  /**
>   *  of_device_is_big_endian - check if a device has BE registers
>   *
> @@ -796,6 +818,9 @@ EXPORT_SYMBOL(of_get_next_available_child);
>   * of_get_next_cpu_node - Iterate on cpu nodes
>   * @prev:	previous child of the /cpus node, or NULL to get first
>   *
> + * Unusable CPUs (those with the status property set to "fail" or "fail-...")
> + * will be skipped.
> + *
>   * Return: A cpu node pointer with refcount incremented, use of_node_put()
>   * on it when done. Returns NULL when prev is the last child. Decrements
>   * the refcount of prev.
> @@ -817,6 +842,8 @@ struct device_node *of_get_next_cpu_node(struct device_node *prev)
>  		of_node_put(node);
>  	}

This comment is being really picky.  I would put the check for status value
of fail after the check of node name.  If Rob is willing to accept this
version I am ok with it.

>  	for (; next; next = next->sibling) {
> +		if (__of_device_is_fail(next))
> +			continue;
>  		if (!(of_node_name_eq(next, "cpu") ||
>  		      __of_node_is_type(next, "cpu")))
>  			continue;
> 

Reviewed-by: Frank Rowand <frank.rowand@...y.com>