linux-kernel - Re: [PATCH v5 06/14] cxl/region: Avoid duplicate call of cxl_port_pick_region

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Message-ID: <86b998af-a496-41fd-a4c7-2d7b622f1d15@intel.com>
Date: Mon, 28 Apr 2025 15:28:44 -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 v5 06/14] cxl/region: Avoid duplicate call of
 cxl_port_pick_region_decoder()



On 4/28/25 2:43 PM, Robert Richter wrote:
> Function cxl_port_pick_region_decoder() is called twice, in
> alloc_region_ref() and cxl_rr_alloc_decoder(). Both functions are
> subsequently called from cxl_port_attach_region(). Make the decoder a
> function argument to both which avoids a duplicate call of
> cxl_port_pick_region_decoder().
> 
> Now, cxl_rr_alloc_decoder() no longer allocates the decoder. Instead,
> the previously picked decoder is assigned to the region reference.
> Hence, rename the function to cxl_rr_assign_decoder().
> 
> Moving the call out of alloc_region_ref() also moves it out of the
> xa_for_each() loop in there. Now, cxld is determined no longer only
> for each auto-generated region, but now once for all regions
> regardless of auto-generated or not. This is fine as the cxld argument
> is needed for all regions in cxl_rr_assign_decoder() and an error would
> be returned otherwise anyway. So it is better to determine the decoder
> in front of all this and fail early if missing instead of running
> through all that code with multiple calls of
> cxl_port_pick_region_decoder().
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Reviewed-by: Gregory Price <gourry@...rry.net>
> Tested-by: Gregory Price <gourry@...rry.net>

Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> ---
>  drivers/cxl/core/region.c | 35 +++++++++++++++++------------------
>  1 file changed, 17 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index e104035e0855..fa3d50982d04 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -931,7 +931,8 @@ static bool auto_order_ok(struct cxl_port *port, struct cxl_region *cxlr_iter,
>  
>  static struct cxl_region_ref *
>  alloc_region_ref(struct cxl_port *port, struct cxl_region *cxlr,
> -		 struct cxl_endpoint_decoder *cxled)
> +		 struct cxl_endpoint_decoder *cxled,
> +		 struct cxl_decoder *cxld)
>  {
>  	struct cxl_region_params *p = &cxlr->params;
>  	struct cxl_region_ref *cxl_rr, *iter;
> @@ -945,9 +946,6 @@ alloc_region_ref(struct cxl_port *port, struct cxl_region *cxlr,
>  			continue;
>  
>  		if (test_bit(CXL_REGION_F_AUTO, &cxlr->flags)) {
> -			struct cxl_decoder *cxld;
> -
> -			cxld = cxl_port_pick_region_decoder(port, cxled, cxlr);
>  			if (auto_order_ok(port, iter->region, cxld))
>  				continue;
>  		}
> @@ -1029,19 +1027,11 @@ static int cxl_rr_ep_add(struct cxl_region_ref *cxl_rr,
>  	return 0;
>  }
>  
> -static int cxl_rr_alloc_decoder(struct cxl_port *port, struct cxl_region *cxlr,
> -				struct cxl_endpoint_decoder *cxled,
> -				struct cxl_region_ref *cxl_rr)
> +static int cxl_rr_assign_decoder(struct cxl_port *port, struct cxl_region *cxlr,
> +				 struct cxl_endpoint_decoder *cxled,
> +				 struct cxl_region_ref *cxl_rr,
> +				 struct cxl_decoder *cxld)
>  {
> -	struct cxl_decoder *cxld;
> -
> -	cxld = cxl_port_pick_region_decoder(port, cxled, cxlr);
> -	if (!cxld) {
> -		dev_dbg(&cxlr->dev, "%s: no decoder available\n",
> -			dev_name(&port->dev));
> -		return -EBUSY;
> -	}
> -
>  	if (cxld->region) {
>  		dev_dbg(&cxlr->dev, "%s: %s already attached to %s\n",
>  			dev_name(&port->dev), dev_name(&cxld->dev),
> @@ -1132,7 +1122,16 @@ static int cxl_port_attach_region(struct cxl_port *port,
>  			nr_targets_inc = true;
>  		}
>  	} else {
> -		cxl_rr = alloc_region_ref(port, cxlr, cxled);
> +		struct cxl_decoder *cxld;
> +
> +		cxld = cxl_port_pick_region_decoder(port, cxled, cxlr);
> +		if (!cxld) {
> +			dev_dbg(&cxlr->dev, "%s: no decoder available\n",
> +				dev_name(&port->dev));
> +			return -EBUSY;
> +		}
> +
> +		cxl_rr = alloc_region_ref(port, cxlr, cxled, cxld);
>  		if (IS_ERR(cxl_rr)) {
>  			dev_dbg(&cxlr->dev,
>  				"%s: failed to allocate region reference\n",
> @@ -1141,7 +1140,7 @@ static int cxl_port_attach_region(struct cxl_port *port,
>  		}
>  		nr_targets_inc = true;
>  
> -		rc = cxl_rr_alloc_decoder(port, cxlr, cxled, cxl_rr);
> +		rc = cxl_rr_assign_decoder(port, cxlr, cxled, cxl_rr, cxld);
>  		if (rc)
>  			goto out_erase;
>  	}