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

[Gavin Shan <gshan@redhat.com>]

On 6/24/21 12:14 PM, Randy Dunlap wrote:
> On 6/23/21 8:37 PM, Gavin Shan wrote:
>> The empty NUMA nodes, where no memory resides in, are allowed. For
>> these empty NUMA nodes, the 'len' of 'reg' property is zero. These
>> empty NUMA node IDs are still valid and parsed. I finds difficulty
>> to get where it's properly documented.
>>
>> So lets add note to empty NUMA nodes in the NUMA binding doc.
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>>   Documentation/devicetree/bindings/numa.txt | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/numa.txt b/Documentation/devicetree/bindings/numa.txt
>> index 21b35053ca5a..c564705c0eac 100644
>> --- a/Documentation/devicetree/bindings/numa.txt
>> +++ b/Documentation/devicetree/bindings/numa.txt
>> @@ -109,6 +109,10 @@ Example:
>>   Dual socket system consists of 2 boards connected through ccn bus and
>>   each board having one socket/soc of 8 cpus, memory and pci bus.
>>   
>> +Note that the empty NUMA nodes, which no memory resides in, are allowed
> 
> Missing period at end of the sentence above.
> 

Oh, Yes. Thanks, Randy. I will replace "resides in" with "resides in period"
in v2.

>> +Their NUMA node IDs are still valid so that memory can be added into these
>> +NUMA nodes through hotplug afterwards.
>> +
>>   	memory@c00000 {
>>   		device_type = "memory";
>>   		reg = <0x0 0xc00000 0x0 0x80000000>;

By the way, I have one more question to check with you if I can. I'm not sure
if dummy and invalid 'unit-address' is allowed in the empty memory node name,
which follows the format "memory@unit-address'.

(1) The 'unit-address' is same thing as to 'base address' for memory node,
     as specified in device-tree specification. I'm not sure if 'base address'
     can be dummy and invalid one since empty memory node doesn't have memory
     at all.

     https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#node-names

(2) I don't find the 'unit-address' is used in linux, but I'm not sure other
     software component like firmware uses it or not.

Thanks,
Gavin