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

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Message-ID: <67edb335dea8c_1a6d929437@dwillia2-xfh.jf.intel.com.notmuch>
Date: Wed, 2 Apr 2025 14:59:17 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Gregory Price <gourry@...rry.net>, <linux-cxl@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, <kernel-team@...a.com>,
	<dan.j.williams@...el.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:
> 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.