Re: [PATCH v3 13/18] cxl/region: Add function to find a port's switch decoder by range

Dave Jiang
2025-02-20T17:23:53Z

On 2/11/25 2:53 AM, Robert Richter wrote:
> Factor out code to find the switch decoder of a port for a specific
> address range. Reuse the code to search a root decoder, create the
> function cxl_port_find_switch_decoder() and rework
> match_root_decoder_by_range() to be usable for switch decoders too.
>
> Signed-off-by: Robert Richter <rrichter@amd.com>
> Reviewed-by: Gregory Price <gourry@gourry.net>
> Tested-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
> drivers/cxl/core/region.c | 48 +++++++++++++++++++++++----------------
> 1 file changed, 28 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index cfcd235f311e..72e991e7d9ab 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3189,28 +3189,44 @@ static int devm_cxl_add_dax_region(struct cxl_region *cxlr)
> return rc;
> }
>
> -static int match_root_decoder_by_range(struct device *dev,
> - const void *data)
> +static int match_decoder_by_range(struct device *dev, const void *data)
> {
> const struct range *r1, *r2 = data;
> - struct cxl_root_decoder *cxlrd;
> + struct cxl_decoder *cxld;
>
> - if (!is_root_decoder(dev))
> + if (!is_switch_decoder(dev))
> return 0;
>
> - cxlrd = to_cxl_root_decoder(dev);
> - r1 = &cxlrd->cxlsd.cxld.hpa_range;
> + cxld = to_cxl_decoder(dev);
> + r1 = &cxld->hpa_range;
> return range_contains(r1, r2);
> }
>
> +static struct cxl_decoder *
> +cxl_port_find_switch_decoder(struct cxl_port *port, struct range *hpa)
> +{
> + /*
> + * device_find_child() increments the reference count of the
> + * the switch decoder's parent port to protect the reference
> + * to its child. The port is already a parent of the endpoint
> + * decoder's port, at least indirectly in the port hierarchy.
> + * Thus, the endpoint already holds a reference for the parent
> + * port of the switch decoder. Free the unnecessary reference
> + * here.
> + */
> + struct device *cxld_dev __free(put_device) =
> + device_find_child(&port->dev, hpa, match_decoder_by_range);
> +
> + return cxld_dev ? to_cxl_decoder(cxld_dev) : NULL;
> +}
> +
> 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 *iter = cxled_to_port(cxled);
> - struct cxl_decoder *cxld = &cxled->cxld;
> + struct cxl_decoder *root, *cxld = &cxled->cxld;
> struct range *hpa = &cxld->hpa_range;
> - struct device *cxlrd_dev;
>
> while (iter && !is_cxl_root(iter))
> iter = to_cxl_port(iter->dev.parent);
> @@ -3218,9 +3234,8 @@ cxl_find_root_decoder(struct cxl_endpoint_decoder *cxled)
> if (!iter)
> return NULL;
>
> - cxlrd_dev = device_find_child(&iter->dev, hpa,
> - match_root_decoder_by_range);
> - if (!cxlrd_dev) {
> + root = cxl_port_find_switch_decoder(iter, hpa);
> + if (!root) {
> dev_err(cxlmd->dev.parent,
> "%s:%s no CXL window for range %#llx:%#llx\n",
> dev_name(&cxlmd->dev), dev_name(&cxld->dev),
> @@ -3228,16 +3243,9 @@ cxl_find_root_decoder(struct cxl_endpoint_decoder *cxled)
> 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);
> +
> + return to_cxl_root_decoder(&root->dev);
> }
>
> static int match_region_by_range(struct device *dev, const void *data)