Re: [PATCH] ACPI: NUMA: Only parse CFMWS at boot when CXL_ACPI is on

[Gregory Price]

On Thu, Mar 05, 2026 at 12:45:39AM +0000, Huang, Kai wrote:
> > 
> > You are taking something away by nature of compiling something out by
> > default that was previously not compiled out by default.
> 
> Yeah, and it is due to "there's a cost" if we don't compile out by default.
> 
> Hope that justifies?

Sorry, i don't mean to come off rough - I don't even necessarily
disagree with the change here, but it is worth taking a moment to
understand whether this is actually a Linux issue or an platform issue.

Up until now there's been some assumption that if a device is attached
there will be CEDT windows - but this would be the first time i've seen
a platform throw up CEDT windows for devices that don't exist.

Anyway, this is good information for Linux to know and worth a comment.
We don't know what other people have built that depend on the current
behavior.

> > 
> > Well, I'm mostly confused why there are CEDT entries for hardware that
> > presumably isn't even there - unless this platform is reserving space
> > for future hotplug.  
> > 
> 
> I think this should be the case.
>

If that's the case then cool :]

May be worth a comment in acpi_numa_init_cxl - something like:

/*
 * Some platforms report CEDT CFMWS for hotplug device support. These
 * windows are unusable without CXL drivers, so don't reserve fake nodes
 * if they're compiled out - it wastes memory on per-node structures.
 */

Reviewed-by: Gregory Price <gourry@xxxxxxxxxx>

~Gregory