linux-kernel - Re: [PATCH v3] cxl: docs/driver-api/conventions resolve conflicts btw CFMWS, LMH, ED

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Message-ID: <aGbcpac1pma1od40@gourry-fedora-PF4VCD3F>
Date: Thu, 3 Jul 2025 15:40:21 -0400
From: Gregory Price <gourry@...rry.net>
To: Dave Jiang <dave.jiang@...el.com>
Cc: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
	linux-cxl@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] cxl: docs/driver-api/conventions resolve conflicts
 btw CFMWS, LMH, ED

On Tue, Jul 01, 2025 at 08:23:57AM -0700, Dave Jiang wrote:
> 
> 
> On 6/23/25 12:19 PM, Gregory Price wrote:
> > On Mon, Jun 23, 2025 at 05:29:02PM +0200, Fabio M. De Francesco wrote:
> >> Add documentation on how to resolve conflicts between CXL Fixed Memory
> >> Windows, Platform Memory Holes, and Endpoint Decoders.
> >>
> >> Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@...ux.intel.com>
> > 
> > I won't block a doc update on a suggestion so
> > 
> > Reviewed-by: Gregory Price <gourry@...rry.net>
> > 
> >> +Platform Firmware (BIOS) might reserve part of physical addresses below
> >> +4 GB (e.g., the Low Memory Hole that describes PCIe memory space for MMIO
> >> +or a requirement for the greater than 8 way interleave CXL regions starting
> >> +at address 0). In that case the Window Size value cannot be anymore
> >> +constrained to the NIW * 256 MB above-mentioned rule.
> > 
> > It might be nice to have a diagram that explains this visually, as it's
> > difficult for me to understand the implications through words alone...
> 
> +1 on request for diagram to explain. We should try to document this issue as clearly as possible. Thank you.
>

At the very least, it would be nice to have an explicitly example that
explains the expected cfmws/decoder configurations that are valid but
"technically" violate the spec

I *think* this basically boils down to "CFMWS size is not aligned, but
all the decoders it targets are"?  If I understand this correctly?

> > 
> > which is likely why the conflict exists in the first place :]
> > 
> > ~Gregory
>