linux-kernel - Re: [PATCH v4 08/14] cxl: Introduce callback for HPA address ranges translation

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Message-ID: <1e3dffee-ffa9-452f-ae9c-83093460103f@intel.com>
Date: Mon, 3 Nov 2025 16:09:08 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Robert Richter <rrichter@....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 Cameron <Jonathan.Cameron@...wei.com>,
 Davidlohr Bueso <dave@...olabs.net>
Cc: linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
 Gregory Price <gourry@...rry.net>,
 "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 v4 08/14] cxl: Introduce callback for HPA address ranges
 translation



On 11/3/25 11:47 AM, Robert Richter wrote:
> Introduce a callback to translate an endpoint's HPA range to the
> address range of the root port which is the System Physical Address
> (SPA) range used by a region. The callback can be set if a platform
> needs to handle address translation.
> 
> The callback is attached to the root port. An endpoint's root port can
> easily be determined in the PCI hierarchy without any CXL specific
> knowledge. This allows the early use of address translation for CXL
> enumeration. Address translation is esp. needed for the detection of
> the root decoders. Thus, the callback is embedded in struct
> cxl_root_ops instead of struct cxl_rd_ops.
> 
> Signed-off-by: Robert Richter <rrichter@....com>

Reviewed-by: Dave Jiang <dave.jiang@...el.com>> ---
>  drivers/cxl/core/region.c | 19 +++++++++++++++++++
>  drivers/cxl/cxl.h         |  1 +
>  2 files changed, 20 insertions(+)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 2dd9e9be4889..379a67cc8e31 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3364,6 +3364,15 @@ static int match_root_decoder(struct device *dev, const void *data)
>  	return range_contains(r1, r2);
>  }
>  
> +static int translate_hpa_range(struct cxl_root *cxl_root,
> +			       struct cxl_region_context *ctx)
> +{
> +	if (!cxl_root->ops.translate_hpa_range)
> +		return 0;
> +
> +	return cxl_root->ops.translate_hpa_range(cxl_root, ctx);
> +}
> +
>  static struct cxl_root_decoder *
>  get_cxl_root_decoder(struct cxl_endpoint_decoder *cxled,
>  		     struct cxl_region_context *ctx)
> @@ -3371,6 +3380,16 @@ get_cxl_root_decoder(struct cxl_endpoint_decoder *cxled,
>  	struct cxl_port *port = cxled_to_port(cxled);
>  	struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
>  	struct device *cxlrd_dev;
> +	int rc;
> +
> +	rc = translate_hpa_range(cxl_root, ctx);
> +	if (rc) {
> +		dev_err(port->uport_dev,
> +			"%s:%s Failed to translate address range %#llx:%#llx\n",
> +			dev_name(&ctx->cxlmd->dev), dev_name(&cxled->cxld.dev),
> +			ctx->hpa_range.start, ctx->hpa_range.end);
> +		return ERR_PTR(rc);
> +	}
>  
>  	cxlrd_dev = device_find_child(&cxl_root->port.dev, &ctx->hpa_range,
>  				      match_root_decoder);
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 9a381c827416..94b9fcc07469 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -644,6 +644,7 @@ struct cxl_root_ops {
>  	int (*qos_class)(struct cxl_root *cxl_root,
>  			 struct access_coordinate *coord, int entries,
>  			 int *qos_class);
> +	int (*translate_hpa_range)(struct cxl_root *cxl_root, void *data);
>  };
>  
>  /**