Re: [PATCH 3/7] cxl/region: Factor out cxl_port_peer_distance()

[Dave Jiang <dave.jiang@intel.com>]

On 10/9/26 1:24 PM, Alison Schofield wrote:
> cxl_port_setup_targets() is nearly 200 lines long and open codes each step
> of adding an endpoint to a port's decoder. One of those steps calculates
> the distance between region positions that share a downstream port.
> 
> Move that calculation to a new helper, cxl_port_peer_distance().
> 
> No functional change.
> 
> Assisted-by: LLM
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>  drivers/cxl/core/region.c | 50 +++++++++++++++++++++++----------------
>  1 file changed, 29 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 1a42753fda48..80c40716c368 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -1432,6 +1432,33 @@ static int check_interleave_cap(struct cxl_decoder *cxld, int iw, int ig)
>  	return 0;
>  }
>  
> +static int cxl_port_peer_distance(struct cxl_port *port, struct cxl_region *cxlr)
> +{
> +	struct cxl_root_decoder *cxlrd = cxlr->cxlrd;
> +	struct cxl_region_ref *cxl_rr_iter;
> +	struct cxl_port *iter = port;
> +	int distance = 1;
> +
> +	/*
> +	 * The "distance" between peer downstream ports represents which
> +	 * endpoint positions in the region interleave a given port can
> +	 * host.
> +	 *
> +	 * For example, at the root of a hierarchy the distance is
> +	 * always 1 as every index targets a different host-bridge. At
> +	 * each subsequent switch level those ports map every Nth region
> +	 * position where N is the width of the switch == distance.
> +	 */
> +	do {
> +		cxl_rr_iter = cxl_rr_load(iter, cxlr);
> +		distance *= cxl_rr_iter->nr_targets;
> +		iter = to_cxl_port(iter->dev.parent);
> +	} while (!is_cxl_root(iter));
> +	distance *= cxlrd->cxlsd.cxld.interleave_ways;
> +
> +	return distance;
> +}
> +
>  static int cxl_port_setup_targets(struct cxl_port *port,
>  				  struct cxl_region *cxlr,
>  				  struct cxl_endpoint_decoder *cxled)
> @@ -1445,7 +1472,6 @@ static int cxl_port_setup_targets(struct cxl_port *port,
>  	struct cxl_region_params *p = &cxlr->params;
>  	struct cxl_decoder *cxld = cxl_rr->decoder;
>  	struct cxl_switch_decoder *cxlsd;
> -	struct cxl_port *iter = port;
>  
>  	/*
>  	 * While root level decoders support x3, x6, x12, switch level
> @@ -1460,27 +1486,9 @@ static int cxl_port_setup_targets(struct cxl_port *port,
>  
>  	cxlsd = to_cxl_switch_decoder(&cxld->dev);
>  	if (cxl_rr->nr_targets_set) {
> -		int i, distance = 1;
> -		struct cxl_region_ref *cxl_rr_iter;
> +		int distance = cxl_port_peer_distance(port, cxlr);
>  
> -		/*
> -		 * The "distance" between peer downstream ports represents which
> -		 * endpoint positions in the region interleave a given port can
> -		 * host.
> -		 *
> -		 * For example, at the root of a hierarchy the distance is
> -		 * always 1 as every index targets a different host-bridge. At
> -		 * each subsequent switch level those ports map every Nth region
> -		 * position where N is the width of the switch == distance.
> -		 */
> -		do {
> -			cxl_rr_iter = cxl_rr_load(iter, cxlr);
> -			distance *= cxl_rr_iter->nr_targets;
> -			iter = to_cxl_port(iter->dev.parent);
> -		} while (!is_cxl_root(iter));
> -		distance *= cxlrd->cxlsd.cxld.interleave_ways;
> -
> -		for (i = 0; i < cxl_rr->nr_targets_set; i++)
> +		for (int i = 0; i < cxl_rr->nr_targets_set; i++)
>  			if (ep->dport == cxlsd->target[i]) {
>  				rc = check_last_peer(cxled, ep, cxl_rr,
>  						     distance);