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

Dave Jiang
2025-02-20T16:48:26Z

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@amd.com>
> Reviewed-by: Gregory Price <gourry@gourry.net>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Tested-by: Gregory Price <gourry@gourry.net>

Reviewed-by: Dave Jiang <dave.jiang@intel.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");