linux-kernel - Re: [PATCH v3 09/18] cxl/region: Factor out code to find the root decoder

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Message-ID: <7ea607c2-b769-4077-9df0-79f79bb0415e@intel.com>
Date: Thu, 20 Feb 2025 09:48:23 -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 v3 09/18] cxl/region: Factor out code to find the root
 decoder



On 2/11/25 2:53 AM, Robert Richter wrote:
> In function cxl_add_to_region() there is code to determine the root
> decoder associated to an endpoint decoder. Factor out that code for
> later reuse. This has the benefit of reducing cxl_add_to_region()'s
> function complexity.
> 
> The reference of cxlrd_dev can be freed earlier. Since the root
> decoder exists as long as the root port exists and the endpoint
> already holds a reference to the root port, this additional reference
> is not needed. Though it looks obvious to use __free() for the
> reference of cxlrd_dev here too, this is done in a later rework. So
> just move the code.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Reviewed-by: Gregory Price <gourry@...rry.net>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Tested-by: Gregory Price <gourry@...rry.net>

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

> ---
>  drivers/cxl/core/region.c | 55 ++++++++++++++++++++++++++-------------
>  1 file changed, 37 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index 0e38bcb43be6..c641c8922455 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3203,6 +3203,38 @@ static int match_root_decoder_by_range(struct device *dev,
>  	return range_contains(r1, r2);
>  }
>  
> +static struct cxl_root_decoder *
> +cxl_find_root_decoder(struct cxl_endpoint_decoder *cxled)
> +{
> +	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> +	struct cxl_port *port = cxled_to_port(cxled);
> +	struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
> +	struct cxl_decoder *cxld = &cxled->cxld;
> +	struct range *hpa = &cxld->hpa_range;
> +	struct device *cxlrd_dev;
> +
> +	cxlrd_dev = device_find_child(&cxl_root->port.dev, hpa,
> +				      match_root_decoder_by_range);
> +	if (!cxlrd_dev) {
> +		dev_err(cxlmd->dev.parent,
> +			"%s:%s no CXL window for range %#llx:%#llx\n",
> +			dev_name(&cxlmd->dev), dev_name(&cxld->dev),
> +			cxld->hpa_range.start, cxld->hpa_range.end);
> +		return NULL;
> +	}
> +
> +	/*
> +	 * device_find_child() created a reference to the root
> +	 * decoder. Since the root decoder exists as long as the root
> +	 * port exists and the endpoint already holds a reference to
> +	 * the root port, this additional reference is not needed.
> +	 * Free it here.
> +	 */
> +	put_device(cxlrd_dev);
> +
> +	return to_cxl_root_decoder(cxlrd_dev);
> +}
> +
>  static int match_region_by_range(struct device *dev, const void *data)
>  {
>  	struct cxl_region_params *p;
> @@ -3314,29 +3346,17 @@ static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
>  
>  int cxl_add_to_region(struct cxl_endpoint_decoder *cxled)
>  {
> -	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> -	struct cxl_port *port = cxled_to_port(cxled);
> -	struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
>  	struct range *hpa = &cxled->cxld.hpa_range;
> -	struct cxl_decoder *cxld = &cxled->cxld;
> -	struct device *cxlrd_dev, *region_dev;
> +	struct device *region_dev;
>  	struct cxl_root_decoder *cxlrd;
>  	struct cxl_region_params *p;
>  	struct cxl_region *cxlr;
>  	bool attach = false;
>  	int rc;
>  
> -	cxlrd_dev = device_find_child(&cxl_root->port.dev, &cxld->hpa_range,
> -				      match_root_decoder_by_range);
> -	if (!cxlrd_dev) {
> -		dev_err(cxlmd->dev.parent,
> -			"%s:%s no CXL window for range %#llx:%#llx\n",
> -			dev_name(&cxlmd->dev), dev_name(&cxld->dev),
> -			cxld->hpa_range.start, cxld->hpa_range.end);
> +	cxlrd = cxl_find_root_decoder(cxled);
> +	if (!cxlrd)
>  		return -ENXIO;
> -	}
> -
> -	cxlrd = to_cxl_root_decoder(cxlrd_dev);
>  
>  	/*
>  	 * Ensure that if multiple threads race to construct_region() for @hpa
> @@ -3354,7 +3374,7 @@ int cxl_add_to_region(struct cxl_endpoint_decoder *cxled)
>  
>  	rc = PTR_ERR_OR_ZERO(cxlr);
>  	if (rc)
> -		goto out;
> +		return rc;
>  
>  	attach_target(cxlr, cxled, -1, TASK_UNINTERRUPTIBLE);
>  
> @@ -3375,8 +3395,7 @@ int cxl_add_to_region(struct cxl_endpoint_decoder *cxled)
>  	}
>  
>  	put_device(region_dev);
> -out:
> -	put_device(cxlrd_dev);
> +
>  	return rc;
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_add_to_region, "CXL");