linux-kernel - Re: [PATCH 3/4 v5] cxl/core: Enable Region creation on x86 with LMH

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Message-ID: <aOQAb9H-wIxc6j31@gourry-fedora-PF4VCD3F>
Date: Mon, 6 Oct 2025 13:46:23 -0400
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, Robert Richter <rrichter@....com>,
	Cheatham Benjamin <benjamin.cheatham@....com>
Subject: Re: [PATCH 3/4 v5] cxl/core: Enable Region creation on x86 with LMH

On Mon, Oct 06, 2025 at 05:58:06PM +0200, Fabio M. De Francesco wrote:
> The CXL Fixed Memory Window Structure (CFMWS) describes zero or more
> Host Physical Address (HPA) windows that are associated with each CXL
> Host Bridge. Each window represents a contiguous HPA that may be
> interleaved with one or more targets (CXL v3.2 - 9.18.1.3).
> 
...
> 
> Cc: Alison Schofield <alison.schofield@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Dave Jiang <dave.jiang@...el.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@...ux.intel.com>

Couple inlines but just nits

Reviewed-by: Gregory Price <gourry@...rry.net>

> @@ -1770,6 +1778,7 @@ static int match_cxlsd_to_cxled_by_range(struct device *dev, const void *data)
>  {
>  	const struct cxl_endpoint_decoder *cxled = data;
>  	struct cxl_switch_decoder *cxlsd;
> +	struct cxl_root_decoder *cxlrd;
>  	const struct range *r1, *r2;
>  
>  	if (!is_switch_decoder(dev))
> @@ -1779,8 +1788,13 @@ static int match_cxlsd_to_cxled_by_range(struct device *dev, const void *data)
>  	r1 = &cxlsd->cxld.hpa_range;
>  	r2 = &cxled->cxld.hpa_range;
>  
> -	if (is_root_decoder(dev))
> -		return range_contains(r1, r2);
> +	if (is_root_decoder(dev)) {
> +		if (range_contains(r1, r2))
> +			return 1;
> +		cxlrd = to_cxl_root_decoder(dev);
> +		if (platform_cxlrd_matches_cxled(cxlrd, cxled))
> +			return 1;
> +	}

Is there any concern for longer term maintainability if addition
match_*() functions are added?  Or is this upkeep just the unfortunate
maintenance cost of supportering the quirk?

>  
>  static struct cxl_decoder *
> @@ -3406,8 +3421,12 @@ static int match_region_to_cxled_by_range(struct device *dev, const void *data)
>  	p = &cxlr->params;
>  
>  	guard(rwsem_read)(&cxl_rwsem.region);
> -	if (p->res && p->res->start == r->start && p->res->end == r->end)
> -		return 1;
> +	if (p->res) {
> +		if (p->res->start == r->start && p->res->end == r->end)
> +			return 1;
> +		if (platform_region_matches_cxld(p, &cxled->cxld))
> +			return 1;
> +	}


if (!p->res)
	return 0;
if (p->res->start == r->start && p->res->end == r->end)
	return 1;
if (platform_region_matches_cxld(p, &cxled->cxld))
	return 1;
return 0;

?

I like flat, but I also dislike not-logic.  Style choice here, unless
others have a strong feeling this is fine.

~Gregory