cxl/core/port: Add switch port enumeration

So far the platorm level CXL resources have been enumerated by the
cxl_acpi driver, and cxl_pci has gathered all the pre-requisite
information it needs to fire up a cxl_mem driver. However, the first
thing the cxl_mem driver will be tasked to do is validate that all the
PCIe Switches in its ancestry also have CXL capabilities and an CXL.mem
link established.

Provide a common mechanism for a CXL.mem endpoint driver to enumerate
all the ancestor CXL ports in the topology and validate CXL.mem
connectivity.

Multiple endpoints may end up racing to establish a shared port in the
topology. This race is resolved via taking the device-lock on a parent
CXL Port before establishing a new child. The winner of the race
establishes the port, the loser simply registers its interest in the
port via 'struct cxl_ep' place-holder reference.

At endpoint teardown the same parent port lock is taken as 'struct
cxl_ep' references are deleted. Last endpoint to drop its reference
unregisters the port.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/164398731146.902644.1029761300481366248.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/acpi.c

@@ -130,21 +130,6 @@ static int cxl_parse_cfmws(union acpi_subtable_headers *header, void *arg,
 	return 0;
 }
 
-static struct cxl_dport *find_dport_by_dev(struct cxl_port *port, struct device *dev)
-{
-	struct cxl_dport *dport;
-
-	cxl_device_lock(&port->dev);
-	list_for_each_entry(dport, &port->dports, list)
-		if (dport->dport == dev) {
-			cxl_device_unlock(&port->dev);
-			return dport;
-		}
-
-	cxl_device_unlock(&port->dev);
-	return NULL;
-}
-
 __mock struct acpi_device *to_cxl_host_bridge(struct device *host,
 					      struct device *dev)
 {
@@ -175,7 +160,7 @@ static int add_host_bridge_uport(struct device *match, void *arg)
 	if (!bridge)
 		return 0;
 
-	dport = find_dport_by_dev(root_port, match);
+	dport = cxl_find_dport_by_dev(root_port, match);
 	if (!dport) {
 		dev_dbg(host, "host bridge expected and not found\n");
 		return 0;

drivers/cxl/cxl.h

@@ -262,8 +262,10 @@ struct cxl_nvdimm {
  * @uport: PCI or platform device implementing the upstream port capability
  * @id: id for port device-name
  * @dports: cxl_dport instances referenced by decoders
+ * @endpoints: cxl_ep instances, endpoints that are a descendant of this port
  * @decoder_ida: allocator for decoder ids
  * @component_reg_phys: component register capability base address (optional)
+ * @dead: last ep has been removed, force port re-creation
  * @depth: How deep this port is relative to the root. depth 0 is the root.
  */
 struct cxl_port {
@@ -271,8 +273,10 @@ struct cxl_port {
 	struct device *uport;
 	int id;
 	struct list_head dports;
+	struct list_head endpoints;
 	struct ida decoder_ida;
 	resource_size_t component_reg_phys;
+	bool dead;
 	unsigned int depth;
 };
 
@@ -292,6 +296,16 @@ struct cxl_dport {
 	struct list_head list;
 };
 
+/**
+ * struct cxl_ep - track an endpoint's interest in a port
+ * @ep: device that hosts a generic CXL endpoint (expander or accelerator)
+ * @list: node on port->endpoints list
+ */
+struct cxl_ep {
+	struct device *ep;
+	struct list_head list;
+};
+
 /*
  * The platform firmware device hosting the root is also the top of the
  * CXL port topology. All other CXL ports have another CXL port as their
@@ -313,9 +327,14 @@ struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
 				   resource_size_t component_reg_phys,
 				   struct cxl_port *parent_port);
 struct cxl_port *find_cxl_root(struct device *dev);
+int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd);
+
 struct cxl_dport *devm_cxl_add_dport(struct cxl_port *port,
 				     struct device *dport, int port_id,
 				     resource_size_t component_reg_phys);
+struct cxl_dport *cxl_find_dport_by_dev(struct cxl_port *port,
+					const struct device *dev);
+
 struct cxl_decoder *to_cxl_decoder(struct device *dev);
 bool is_root_decoder(struct device *dev);
 bool is_cxl_decoder(struct device *dev);