linux-kernel - Re: [PATCH] cxl: core/region - ignore interleave granularity when ways=1

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Message-ID: <Z-27DR_D47HkuR-6@gourry-fedora-PF4VCD3F>
Date: Wed, 2 Apr 2025 18:32:45 -0400
From: Gregory Price <gourry@...rry.net>
To: Dan Williams <dan.j.williams@...el.com>
Cc: linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...a.com, vishal.l.verma@...el.com,
	dave.jiang@...el.com, dave@...olabs.net,
	jonathan.cameron@...wei.com, alison.schofield@...el.com,
	ira.weiny@...el.com
Subject: Re: [PATCH] cxl: core/region - ignore interleave granularity when
 ways=1

On Wed, Apr 02, 2025 at 02:59:17PM -0700, Dan Williams wrote:
> Gregory Price wrote:
> > When validating decoder IW/IG when setting up regions, the granularity
> > is irrelevant when iw=1 - all accesses will always route to the only
> > target anyway - so all ig values are "correct". Loosen the requirement
> > that `ig = (parent_iw * parent_ig)` when iw=1.
> 
> Can you say a bit more here about the real world impact like we chatted
> about on Discord? Something like:
> 
> ---
> The platform BIOS on "platform-X" specifies a 512-byte
> interleave-granularity CXL Window when 256-byte is expected. This leads
> to Linux erroneously rejecting the region configuration of 2 devices
> attached to an x1 host bridge.
> ---
> 
> That way distros and platform-X folks can flag the importance of this fix.

Would like this inline or just in the changelog?

~Gregory