linux-kernel - Re: [PATCH v2 02/15] cxl: Introduce callback to translate an HPA range from a port to its parent

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Message-ID: <fc5ab516-3b73-4c6f-8c21-4ad643ff3320@intel.com>
Date: Thu, 20 Feb 2025 14:19:26 -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>
Subject: Re: [PATCH v2 02/15] cxl: Introduce callback to translate an HPA
 range from a port to its parent



On 2/18/25 6:23 AM, Robert Richter wrote:
> To enable address translation, the endpoint's HPA range must be
> translated to each of the parent port's address ranges up to the root
> decoder. Traverse the decoder and port hierarchy from the endpoint up
> to the root port and apply platform specific translation functions to
> determine the next HPA range of the parent port where needed:
> 
>   if (cxl_port->to_hpa)
>     hpa = cxl_port->to_hpa(cxl_decoder, hpa)
> 
> The root port's HPA range is equivalent to the system's SPA range.
> 
> Introduce a callback to translate an HPA range from a port to its
> parent.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Reviewed-by: Gregory Price <gourry@...rry.net>
> ---
>  drivers/cxl/cxl.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)

With such a small change, I would fold this into the patch where you are using it. 

> 
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index b19ba47242c6..17496784f021 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -418,6 +418,15 @@ struct cxl_switch_decoder {
>  	struct cxl_dport *target[];
>  };
>  
> +/**
> + * cxl_to_hpa_fn - type of a callback function to translate an HPA
> + * @cxld: cxl_decoder to translate from
> + * @hpa: HPA of the @cxld decoder's address range
> + *
> + * The callback translates a decoder's HPA to the next upper domain
> + * which is the address range of the decoder's parent port. The return
> + * value is the translated HPA on success or ULLONG_MAX otherwise.
> + */
>  typedef u64 (*cxl_to_hpa_fn)(struct cxl_decoder *cxld, u64 hpa);
>  
>  /**
> @@ -581,6 +590,7 @@ struct cxl_dax_region {
>   * @parent_dport: dport that points to this port in the parent
>   * @decoder_ida: allocator for decoder ids
>   * @reg_map: component and ras register mapping parameters
> + * @to_hpa: Callback to translate a child port's decoder address to the port's HPA address range
>   * @nr_dports: number of entries in @dports
>   * @hdm_end: track last allocated HDM decoder instance for allocation ordering
>   * @commit_end: cursor to track highest committed decoder for commit ordering
> @@ -602,6 +612,7 @@ struct cxl_port {
>  	struct cxl_dport *parent_dport;
>  	struct ida decoder_ida;
>  	struct cxl_register_map reg_map;
> +	cxl_to_hpa_fn to_hpa;
>  	int nr_dports;
>  	int hdm_end;
>  	int commit_end;