linux-kernel - Re: [PATCH v1 23/29] cxl/region: Use root decoders interleaving parameters to create a region

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Message-ID: <Z68_4Lm001A_aYjM@rric.localdomain>
Date: Fri, 14 Feb 2025 14:06:40 +0100
From: Robert Richter <rrichter@....com>
To: Alison Schofield <alison.schofield@...el.com>
Cc: Vishal Verma <vishal.l.verma@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org, Gregory Price <gourry@...rry.net>,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
	Terry Bowman <terry.bowman@....com>
Subject: Re: [PATCH v1 23/29] cxl/region: Use root decoders interleaving
 parameters to create a region

On 13.01.25 09:48:47, Alison Schofield wrote:
> On Tue, Jan 07, 2025 at 03:10:09PM +0100, Robert Richter wrote:
> > Endpoints requiring address translation might not be aware of the
> > system's interleaving configuration. Instead, interleaving can be
> > configured on an upper memory domain (from an endpoint view) and thus
> > is not visible to the endpoint. For region creation this might cause
> > an invalid interleaving config that does not match the CFMWS entries.
> > 
> > Use the interleaving configuration of the root decoders to create a
> > region which bases on CFMWS entries. This always matches the system's
> > interleaving configuration and is independent of the underlying memory
> > topology.
> 
> This sounds like a restriction, more restrictive than present.
> 
> Won't it block all region interleave ways greater than root decoder
> interleave ways? ie. disallows 2, 2+2, 2+2+2, 4, etc.

Yes, a combination of all decoders from the endpoint up to the root
result in the interleaving config. This will be fixed in the next
version.

Thanks for catching this,

-Robert