cxl/mem: Enumerate port targets before adding endpoints

The port scanning algorithm in devm_cxl_enumerate_ports() walks up the
topology and adds cxl_port objects starting from the root down to the
endpoint. When those ports are initially created they know all their
dports, but they do not know the downstream cxl_port instance that
represents the next descendant in the topology. Rework create_endpoint()
into devm_cxl_add_endpoint() that enumerates the downstream cxl_port
topology into each port's 'struct cxl_ep' record for each endpoint it
that the port is an ancestor.

Reviewed-by: Jonathan Cameron <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dan Williams <[e-mail]>

drivers/cxl/core/port.c

···
 	return xa_load(&port->endpoints, (unsigned long)&cxlmd->dev);
 }
 
+int devm_cxl_add_endpoint(struct cxl_memdev *cxlmd,
+			  struct cxl_dport *parent_dport)
+{
+	struct cxl_port *parent_port = parent_dport->port;
+	struct cxl_dev_state *cxlds = cxlmd->cxlds;
+	struct cxl_port *endpoint, *iter, *down;
+	int rc;
+
+	/*
+	 * Now that the path to the root is established record all the
+	 * intervening ports in the chain.
+	 */
+	for (iter = parent_port, down = NULL; !is_cxl_root(iter);
+	     down = iter, iter = to_cxl_port(iter->dev.parent)) {
+		struct cxl_ep *ep;
+
+		ep = cxl_ep_load(iter, cxlmd);
+		ep->next = down;
+	}
+
+	endpoint = devm_cxl_add_port(&parent_port->dev, &cxlmd->dev,
+				     cxlds->component_reg_phys, parent_dport);
+	if (IS_ERR(endpoint))
+		return PTR_ERR(endpoint);
+
+	dev_dbg(&cxlmd->dev, "add: %s\n", dev_name(&endpoint->dev));
+
+	rc = cxl_endpoint_autoremove(cxlmd, endpoint);
+	if (rc)
+		return rc;
+
+	if (!endpoint->dev.driver) {
+		dev_err(&cxlmd->dev, "%s failed probe\n",
+			dev_name(&endpoint->dev));
+		return -ENXIO;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(devm_cxl_add_endpoint, CXL);
+
 static void cxl_detach_ep(void *data)
 {
 	struct cxl_memdev *cxlmd = data;

drivers/cxl/cxl.h

···
  * struct cxl_ep - track an endpoint's interest in a port
  * @ep: device that hosts a generic CXL endpoint (expander or accelerator)
  * @dport: which dport routes to this endpoint on @port
+ * @next: cxl switch port across the link attached to @dport NULL if
+ *	  attached to an endpoint
  */
 struct cxl_ep {
 	struct device *ep;
 	struct cxl_dport *dport;
+	struct cxl_port *next;
 };
 
 /*
···
 struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
 				   resource_size_t component_reg_phys,
 				   struct cxl_dport *parent_dport);
+int devm_cxl_add_endpoint(struct cxl_memdev *cxlmd,
+			  struct cxl_dport *parent_dport);
 struct cxl_port *find_cxl_root(struct device *dev);
 int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd);
 int cxl_bus_rescan(void);

drivers/cxl/mem.c

···
  * in higher level operations.
  */
 
-static int create_endpoint(struct cxl_memdev *cxlmd,
-			   struct cxl_dport *parent_dport)
-{
-	struct cxl_port *parent_port = parent_dport->port;
-	struct cxl_dev_state *cxlds = cxlmd->cxlds;
-	struct cxl_port *endpoint;
-	int rc;
-
-	endpoint = devm_cxl_add_port(&parent_port->dev, &cxlmd->dev,
-				     cxlds->component_reg_phys, parent_dport);
-	if (IS_ERR(endpoint))
-		return PTR_ERR(endpoint);
-
-	dev_dbg(&cxlmd->dev, "add: %s\n", dev_name(&endpoint->dev));
-
-	rc = cxl_endpoint_autoremove(cxlmd, endpoint);
-	if (rc)
-		return rc;
-
-	if (!endpoint->dev.driver) {
-		dev_err(&cxlmd->dev, "%s failed probe\n",
-			dev_name(&endpoint->dev));
-		return -ENXIO;
-	}
-
-	return 0;
-}
-
 static void enable_suspend(void *data)
 {
 	cxl_mem_active_dec();
···
 		goto unlock;
 	}
 
-	rc = create_endpoint(cxlmd, dport);
+	rc = devm_cxl_add_endpoint(cxlmd, dport);
 unlock:
 	device_unlock(&parent_port->dev);
 	put_device(&parent_port->dev);