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

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Message-ID: <aFmo18OEZGMA2HU8@gourry-fedora-PF4VCD3F>
Date: Mon, 23 Jun 2025 14:19:51 -0500
From: Gregory Price <gourry@...rry.net>
To: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
Cc: linux-cxl@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.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 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...

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

~Gregory