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

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Message-ID: <67edbba5e09df_1a6d92949@dwillia2-xfh.jf.intel.com.notmuch>
Date: Wed, 2 Apr 2025 15:35:17 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Gregory Price <gourry@...rry.net>, 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

Gregory Price wrote:
> 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?

Changelog is fine, because this more about routing the fix than
explaining the code.