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Date: Fri, 25 Jun 2021 18:36:48 +1000
From: Gavin Shan <gshan@...hat.com>
To: Andrew Jones <drjones@...hat.com>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
rdunlap@...radead.org, robh+dt@...nel.org, shan.gavin@...il.com
Subject: Re: [PATCH v4] Documentation, dt, numa: Add note to empty NUMA node
On 6/25/21 5:06 PM, Andrew Jones wrote:
> On Fri, Jun 25, 2021 at 09:02:17AM +0200, Andrew Jones wrote:
>> On Fri, Jun 25, 2021 at 01:23:38PM +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 can be
>>> added to them through hotplug afterwards. I finds difficulty to
>>> get where it's properly documented.
>>>
>>> So lets add note to empty memory 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..0fc882e44270 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 empty memory nodes, which no memory resides in, are allowed.
>>> +The NUMA node IDs in these empty memory nodes are still valid, but
>>> +memory can be added into them through hotplug afterwards.
>>
>> Please change the second sentence to:
>>
>> The NUMA node IDs in these empty memory nodes are still valid and
>> memory may be added into them through hotplug afterwards.
>>
>> But, this doesn't look like the right place for this paragraph. You're
>> adding the paragraph to the example section, but the example doesn't have
>> any empty memory nodes.
>>
>> I think the paragraph should be added to section "2 - numa-node-id" and an
>
> Or maybe even create a new section for it.
>
>> example empty memory node should be provided. Also, the commit message
>> talks about the length of 'reg' being zero, which is an important
>> distinction which should also be documented.
>>
Drew, thanks for your comments. Yeah, it sounds sensible to create
a new section for it and an example would be more helpful. Please
check if below changes are fine to you. I probably need Randy's review
again.
I'm trying to avoid too many revisions for this sort of trivial patch,
even though I already had. However, it's time frame for v5.14 and I'm
pushing this to be merged during the cycle.
--- a/Documentation/devicetree/bindings/numa.txt
+++ b/Documentation/devicetree/bindings/numa.txt
@@ -103,7 +103,65 @@ Example:
};
==============================================================================
-4 - Example dts
+4 - Empty memory node
+==============================================================================
+
+Empty memory nodes, which no memory resides in, are allowed. The 'length'
+field of 'reg' property is zero, but 'base-address' is dummy and invalid
+for these empty memory nodes. However, the NUMA node IDs and distance maps
+for them are still valid, but 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@...0000000 {
+ device_type = "memory";
+ reg = <0x0 0x80000000 0x0 0x80000000>;
+ numa-node-id = <1>;
+ };
+
+ /* Empty memory node */
+ memory@...00000000 {
+ device_type = "memory";
+ reg = <0x1 0x0 0x0 0x0>;
+ numa-node-id = <2>;
+ };
+
+ /* Empty memory node */
+ memory@...80000000 {
+ device_type = "memory";
+ reg = <0x1 0x80000000 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
Thanks,
Gavin
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