linux-kernel - Re: [PATCH v3 11/11] cxl: Enable AMD Zen5 address translation using ACPI PRMT

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Message-ID: <aNQl2ogOPKid7yyp@gourry-fedora-PF4VCD3F>
Date: Wed, 24 Sep 2025 13:09:46 -0400
From: Gregory Price <gourry@...rry.net>
To: Robert Richter <rrichter@....com>
Cc: 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 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,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
	Terry Bowman <terry.bowman@....com>,
	Joshua Hahn <joshua.hahnjy@...il.com>
Subject: Re: [PATCH v3 11/11] cxl: Enable AMD Zen5 address translation using
 ACPI PRMT

On Fri, Sep 12, 2025 at 04:45:13PM +0200, Robert Richter wrote:
> +static void cxl_prm_init(struct cxl_port *port)
> +{
> +	u64 spa;
> +	struct prm_cxl_dpa_spa_data data = { .out = &spa, };
> +	int rc;
> +
> +	if (!check_prm_address_translation(port))
> +		return;
> +
> +	/* Check kernel (-EOPNOTSUPP) and firmware support (-ENODEV) */
> +	rc = acpi_call_prm_handler(prm_cxl_dpa_spa_guid, &data);
> +	if (rc == -EOPNOTSUPP || rc == -ENODEV)
> +		return;
> +
> +	port->to_hpa = cxl_prm_to_hpa;
> +
> +	dev_dbg(port->host_bridge, "PRM address translation enabled for %s.\n",
> +		dev_name(&port->dev));
> +}

Is it possible that the PRMT function is present but uninitialize?
For example if expanders are not in a normalized address mode.

This code would likely still add the to_hpa() function reference even
if the underlying PRMT function hasn't been set up for translation.

~Gregory