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

[Gavin Shan]

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@xxxxxxxxxx>
> > ---
> >   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