cxl/region: Attach endpoint decoders

CXL regions (interleave sets) are made up of a set of memory devices
where each device maps a portion of the interleave with one of its
decoders (see CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure).
As endpoint decoders are identified by a provisioning tool they can be
added to a region provided the region interleave properties are set
(way, granularity, HPA) and DPA has been assigned to the decoder.

The attach event triggers several validation checks, for example:
- is the DPA sized appropriately for the region
- is the decoder reachable via the host-bridges identified by the
  region's root decoder
- is the device already active in a different region position slot
- are there already regions with a higher HPA active on a given port
  (per CXL 2.0 8.2.5.12.20 Committing Decoder Programming)

...and the attach event affords an opportunity to collect data and
resources relevant to later programming the target lists in switch
decoders, for example:
- allocate a decoder at each cxl_port in the decode chain
- for a given switch port, how many the region's endpoints are hosted
  through the port
- how many unique targets (next hops) does a port need to map to reach
  those endpoints

The act of reconciling this information and deploying it to the decoder
configuration is saved for a follow-on patch.

Co-developed-by: Ben Widawsky <bwidawsk@kernel.org>
Signed-off-by: Ben Widawsky <bwidawsk@kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/165784337277.1758207.4108508181328528703.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/core.h

@@ -41,6 +41,13 @@ resource_size_t cxl_dpa_size(struct cxl_endpoint_decoder *cxled);
 resource_size_t cxl_dpa_resource_start(struct cxl_endpoint_decoder *cxled);
 extern struct rw_semaphore cxl_dpa_rwsem;
 
+bool is_switch_decoder(struct device *dev);
+static inline struct cxl_ep *cxl_ep_load(struct cxl_port *port,
+					 struct cxl_memdev *cxlmd)
+{
+	return xa_load(&port->endpoints, (unsigned long)&cxlmd->dev);
+}
+
 int cxl_memdev_init(void);
 void cxl_memdev_exit(void);
 void cxl_mbox_init(void);

drivers/cxl/core/port.c

@@ -448,7 +448,7 @@ bool is_root_decoder(struct device *dev)
 }
 EXPORT_SYMBOL_NS_GPL(is_root_decoder, CXL);
 
-static bool is_switch_decoder(struct device *dev)
+bool is_switch_decoder(struct device *dev)
 {
 	return is_root_decoder(dev) || dev->type == &cxl_decoder_switch_type;
 }
@@ -504,6 +504,7 @@ static void cxl_port_release(struct device *dev)
 		cxl_ep_remove(port, ep);
 	xa_destroy(&port->endpoints);
 	xa_destroy(&port->dports);
+	xa_destroy(&port->regions);
 	ida_free(&cxl_port_ida, port->id);
 	kfree(port);
 }
@@ -635,6 +636,7 @@ static struct cxl_port *cxl_port_alloc(struct device *uport,
 	port->hdm_end = -1;
 	xa_init(&port->dports);
 	xa_init(&port->endpoints);
+	xa_init(&port->regions);
 
 	device_initialize(dev);
 	lockdep_set_class_and_subclass(&dev->mutex, &cxl_port_key, port->depth);
@@ -1109,12 +1111,6 @@ static void reap_dports(struct cxl_port *port)
 	}
 }
 
-static struct cxl_ep *cxl_ep_load(struct cxl_port *port,
-				  struct cxl_memdev *cxlmd)
-{
-	return xa_load(&port->endpoints, (unsigned long)&cxlmd->dev);
-}
-
 int devm_cxl_add_endpoint(struct cxl_memdev *cxlmd,
 			  struct cxl_dport *parent_dport)
 {