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

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Message-ID: <4b7aae44-8287-5a5a-7d78-0d4fcbfd2c65@quicinc.com>
Date:   Fri, 26 Nov 2021 12:13:32 +0530
From:   Sai Prakash Ranjan <quic_saipraka@...cinc.com>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>
CC:     <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] of: base: Skip CPU nodes with "fail"/"fail-..." status

On 11/22/2021 5:15 PM, 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.
>
> References:
> - https://www.lkml.org/lkml/2020/8/26/1237
> - https://www.spinics.net/lists/devicetree-spec/msg01007.html
> - 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);
>   	}
>   	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;

Thanks for the patch, we have a similar usecase coming up and this is 
very useful than fixing up phandles.

Tested-by: Sai Prakash Ranjan <quic_saipraka@...cinc.com>

-Sai