linux-kernel - Re: [LSF/MM] CXL Boot to Bash - Section 0: ACPI and Linux Resources

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Message-ID: <67e550f39d57d_13cb2941c@dwillia2-mobl3.amr.corp.intel.com.notmuch>
Date: Thu, 27 Mar 2025 09:21:55 -0400
From: Dan Williams <dan.j.williams@...el.com>
To: Gregory Price <gourry@...rry.net>, Yuquan Wang
	<wangyuquan1236@...tium.com.cn>
CC: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	<lsf-pc@...ts.linux-foundation.org>, <linux-mm@...ck.org>,
	<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [LSF/MM] CXL Boot to Bash - Section 0: ACPI and Linux Resources

Gregory Price wrote:
> On Thu, Mar 27, 2025 at 05:34:54PM +0800, Yuquan Wang wrote:
> > 
> > In the future, srat.c would add one seperate NUMA node for each
> > Generic Port in SRAT.
> > 
> > System firmware should know the performance characteristics between
> > CPU/GI to the GP, and the static HMAT should include this coordinate.
> > 
> > Is my understanding right?
> > 
> > 
> 
> HMAT is static configuration data.  A GI/GP might not have its
> performance data known until the device is added.

The GP data is static and expected to be valid for all host bridges in
advance of any devices arriving.

> In this case, the HMAT may only contain generic (inaccurate)
> information - or more likely just nothing. 

It may contain incomplete information, but not dynamic information.
Now, technically ACPI does allow for a notification to replace the
static HMAT, i.e.  acpi_evaluate_object(..., "_HMA", ...), but Linux
does not support that. I am not aware of any platform that implements
that.

> It's up to the platform vendor.

Hopefully saying the above out loud manifests that Linux never needs to
worry about dynamic GP information in the future and all the other
dynamics remain in the physical hotplug domain.