Re: [PATCH v5] Documentation, dt, numa: Add note to empty NUMA node

[Rob Herring <robh@kernel.org>]

On Mon, Jun 28, 2021 at 05:34:11PM +0800, Gavin Shan wrote:
> The empty memory nodes, where no memory resides in, are allowed.
> For these empty memory nodes, the 'len' of 'reg' property is zero.
> The NUMA node IDs are still valid and parsed, but memory may be
> added to them through hotplug afterwards. I finds difficulty to
> get where it's properly documented.

This is already in use? If so, what platform(s)?

> So lets add a section for empty memory nodes in NUMA binding
> document. Also, the 'unit-address', equivalent to 'base-address'
> in the 'reg' property of these empty memory nodes is suggested to
> be the summation of highest memory address plus the NUMA node ID.

What purpose does this serve? The kernel won't do anything with it other 
than validate the numa-node-id range.

> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
> v5: Separate section for empty memory node
> ---
>  Documentation/devicetree/bindings/numa.txt | 61 +++++++++++++++++++++-
>  1 file changed, 60 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/numa.txt b/Documentation/devicetree/bindings/numa.txt
> index 21b35053ca5a..230c734af948 100644
> --- a/Documentation/devicetree/bindings/numa.txt
> +++ b/Documentation/devicetree/bindings/numa.txt
> @@ -103,7 +103,66 @@ Example:
>  		};
>  
>  ==============================================================================
> -4 - Example dts
> +4 - Empty memory nodes
> +==============================================================================
> +
> +Empty memory nodes, which no memory resides in, are allowed. The 'length'
> +field of the 'reg' property is zero, but the 'base-address' is a dummy
> +address and invalid. The 'base-address' could be the summation of highest
> +memory address plus the NUMA node ID. However, the NUMA node IDs and
> +distance maps are still valid and memory may be added into them through
> +hotplug afterwards.
> +
> +Example:
> +
> +	memory@0 {
> +		device_type = "memory";
> +		reg = <0x0 0x0 0x0 0x80000000>;
> +		numa-node-id = <0>;
> +	};
> +
> +	memory@0x80000000 {

unit-address should not have '0x'.

> +		device_type = "memory";
> +		reg = <0x0 0x80000000 0x0 0x80000000>;
> +		numa-node-id = <1>;
> +	};
> +
> +	/* Empty memory node */
> +	memory@0x100000002 {
> +		device_type = "memory";
> +		reg = <0x1 0x2 0x0 0x0>;
> +		numa-node-id = <2>;
> +	};
> +
> +	/* Empty memory node */
> +	memory@0x100000003 {
> +		device_type = "memory";
> +		reg = <0x1 0x3 0x0 0x0>;
> +		numa-node-id = <3>;
> +	};
> +
> +	distance-map {
> +		compatible = "numa-distance-map-v1";
> +		distance-matrix = <0 0  10>,
> +				  <0 1  20>,
> +				  <0 2  40>,
> +				  <0 3  20>,
> +				  <1 0  20>,
> +				  <1 1  10>,
> +				  <1 2  20>,
> +				  <1 3  40>,
> +				  <2 0  40>,
> +				  <2 1  20>,
> +				  <2 2  10>,
> +				  <2 3  20>,
> +				  <3 0  20>,
> +				  <3 1  40>,
> +				  <3 2  20>,
> +				  <3 3  10>;
> +	};
> +
> +==============================================================================
> +5 - Example dts
>  ==============================================================================
>  
>  Dual socket system consists of 2 boards connected through ccn bus and
> -- 
> 2.23.0
> 
>