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

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Date:   Wed, 23 Jun 2021 22:37:40 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Gavin Shan <gshan@...hat.com>, devicetree@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, robh+dt@...nel.org,
        drjones@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH] Documentation, dt, numa: Add note to empty NUMA node

On 6/23/21 9:58 PM, Gavin Shan wrote:
> 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@...hat.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.

Cute. Would it help if I replaced "period" with Missing "full stop" or '.' at the end
of the sentence?

>>> +Their NUMA node IDs are still valid so that memory can be added into these
>>> +NUMA nodes through hotplug afterwards.
>>> +
>>>       memory@...000 {
>>>           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@...t-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.

I have no idea about that.