cxl/region: Program target lists

Once the region's interleave geometry (ways, granularity, size) is
established and all the endpoint decoder targets are assigned, the next
phase is to program all the intermediate decoders. Specifically, each
CXL switch in the path between the endpoint and its CXL host-bridge
(including the logical switch internal to the host-bridge) needs to have
its decoders programmed and the target list order assigned.

The difficulty in this implementation lies in determining which endpoint
decoder ordering combinations are valid. Consider the cxl_test case of 2
host bridges, each of those host-bridges attached to 2 switches, and
each of those switches attached to 2 endpoints for a potential 8-way
interleave. The x2 interleave at the host-bridge level requires that all
even numbered endpoint decoder positions be located on the "left" hand
side of the topology tree, and the odd numbered positions on the other.
The endpoints that are peers on the same switch need to have a position
that can be routed with a dedicated address bit per-endpoint. See
check_last_peer() for the details.

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

drivers/cxl/core/core.h

···
 extern struct rw_semaphore cxl_dpa_rwsem;
 
 bool is_switch_decoder(struct device *dev);
+struct cxl_switch_decoder *to_cxl_switch_decoder(struct device *dev);
 static inline struct cxl_ep *cxl_ep_load(struct cxl_port *port,
 					 struct cxl_memdev *cxlmd)
 {
+	if (!port)
+		return NULL;
+
 	return xa_load(&port->endpoints, (unsigned long)&cxlmd->dev);
 }
 

drivers/cxl/core/port.c

···
 	return offset;
 }
 
-static struct cxl_switch_decoder *to_cxl_switch_decoder(struct device *dev);
-
 static ssize_t target_list_show(struct device *dev,
 				struct device_attribute *attr, char *buf)
 {
···
 }
 EXPORT_SYMBOL_NS_GPL(to_cxl_endpoint_decoder, CXL);
 
-static struct cxl_switch_decoder *to_cxl_switch_decoder(struct device *dev)
+struct cxl_switch_decoder *to_cxl_switch_decoder(struct device *dev)
 {
 	if (dev_WARN_ONCE(dev, !is_switch_decoder(dev),
 			  "not a cxl_switch_decoder device\n"))

drivers/cxl/core/region.c

···
 		return NULL;
 	cxl_rr->port = port;
 	cxl_rr->region = cxlr;
+	cxl_rr->nr_targets = 1;
 	xa_init(&cxl_rr->endpoints);
 
 	rc = xa_insert(&port->regions, (unsigned long)cxlr, cxl_rr, GFP_KERNEL);
···
 	struct cxl_decoder *cxld = cxl_rr->decoder;
 	struct cxl_ep *ep = cxl_ep_load(port, cxled_to_memdev(cxled));
 
-	rc = xa_insert(&cxl_rr->endpoints, (unsigned long)cxled, ep,
-			 GFP_KERNEL);
-	if (rc)
-		return rc;
+	if (ep) {
+		rc = xa_insert(&cxl_rr->endpoints, (unsigned long)cxled, ep,
+			       GFP_KERNEL);
+		if (rc)
+			return rc;
+	}
 	cxl_rr->nr_eps++;
 
 	if (!cxld->region) {
···
 		goto out_erase;
 	}
 
+	dev_dbg(&cxlr->dev,
+		"%s:%s %s add: %s:%s @ %d next: %s nr_eps: %d nr_targets: %d\n",
+		dev_name(port->uport), dev_name(&port->dev),
+		dev_name(&cxld->dev), dev_name(&cxlmd->dev),
+		dev_name(&cxled->cxld.dev), pos,
+		ep ? ep->next ? dev_name(ep->next->uport) :
+				      dev_name(&cxlmd->dev) :
+			   "none",
+		cxl_rr->nr_eps, cxl_rr->nr_targets);
+
 	return 0;
 out_erase:
 	if (cxl_rr->nr_eps == 0)
···
 				   struct cxl_endpoint_decoder *cxled)
 {
 	struct cxl_region_ref *cxl_rr;
-	struct cxl_ep *ep;
+	struct cxl_ep *ep = NULL;
 
 	lockdep_assert_held_write(&cxl_region_rwsem);
 
···
 	if (!cxl_rr)
 		return;
 
-	ep = xa_erase(&cxl_rr->endpoints, (unsigned long)cxled);
+	/*
+	 * Endpoint ports do not carry cxl_ep references, and they
+	 * never target more than one endpoint by definition
+	 */
+	if (cxl_rr->decoder == &cxled->cxld)
+		cxl_rr->nr_eps--;
+	else
+		ep = xa_erase(&cxl_rr->endpoints, (unsigned long)cxled);
 	if (ep) {
 		struct cxl_ep *ep_iter;
 		unsigned long index;
···
 
 	if (cxl_rr->nr_eps == 0)
 		free_region_ref(cxl_rr);
+}
+
+static int check_last_peer(struct cxl_endpoint_decoder *cxled,
+			   struct cxl_ep *ep, struct cxl_region_ref *cxl_rr,
+			   int distance)
+{
+	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
+	struct cxl_region *cxlr = cxl_rr->region;
+	struct cxl_region_params *p = &cxlr->params;
+	struct cxl_endpoint_decoder *cxled_peer;
+	struct cxl_port *port = cxl_rr->port;
+	struct cxl_memdev *cxlmd_peer;
+	struct cxl_ep *ep_peer;
+	int pos = cxled->pos;
+
+	/*
+	 * If this position wants to share a dport with the last endpoint mapped
+	 * then that endpoint, at index 'position - distance', must also be
+	 * mapped by this dport.
+	 */
+	if (pos < distance) {
+		dev_dbg(&cxlr->dev, "%s:%s: cannot host %s:%s at %d\n",
+			dev_name(port->uport), dev_name(&port->dev),
+			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev), pos);
+		return -ENXIO;
+	}
+	cxled_peer = p->targets[pos - distance];
+	cxlmd_peer = cxled_to_memdev(cxled_peer);
+	ep_peer = cxl_ep_load(port, cxlmd_peer);
+	if (ep->dport != ep_peer->dport) {
+		dev_dbg(&cxlr->dev,
+			"%s:%s: %s:%s pos %d mismatched peer %s:%s\n",
+			dev_name(port->uport), dev_name(&port->dev),
+			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev), pos,
+			dev_name(&cxlmd_peer->dev),
+			dev_name(&cxled_peer->cxld.dev));
+		return -ENXIO;
+	}
+
+	return 0;
+}
+
+static int cxl_port_setup_targets(struct cxl_port *port,
+				  struct cxl_region *cxlr,
+				  struct cxl_endpoint_decoder *cxled)
+{
+	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
+	int parent_iw, parent_ig, ig, iw, rc, inc = 0, pos = cxled->pos;
+	struct cxl_port *parent_port = to_cxl_port(port->dev.parent);
+	struct cxl_region_ref *cxl_rr = cxl_rr_load(port, cxlr);
+	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
+	struct cxl_ep *ep = cxl_ep_load(port, cxlmd);
+	struct cxl_region_params *p = &cxlr->params;
+	struct cxl_decoder *cxld = cxl_rr->decoder;
+	struct cxl_switch_decoder *cxlsd;
+	u16 eig, peig;
+	u8 eiw, peiw;
+
+	/*
+	 * While root level decoders support x3, x6, x12, switch level
+	 * decoders only support powers of 2 up to x16.
+	 */
+	if (!is_power_of_2(cxl_rr->nr_targets)) {
+		dev_dbg(&cxlr->dev, "%s:%s: invalid target count %d\n",
+			dev_name(port->uport), dev_name(&port->dev),
+			cxl_rr->nr_targets);
+		return -EINVAL;
+	}
+
+	cxlsd = to_cxl_switch_decoder(&cxld->dev);
+	if (cxl_rr->nr_targets_set) {
+		int i, distance;
+
+		distance = p->nr_targets / cxl_rr->nr_targets;
+		for (i = 0; i < cxl_rr->nr_targets_set; i++)
+			if (ep->dport == cxlsd->target[i]) {
+				rc = check_last_peer(cxled, ep, cxl_rr,
+						     distance);
+				if (rc)
+					return rc;
+				goto out_target_set;
+			}
+		goto add_target;
+	}
+
+	if (is_cxl_root(parent_port)) {
+		parent_ig = cxlrd->cxlsd.cxld.interleave_granularity;
+		parent_iw = cxlrd->cxlsd.cxld.interleave_ways;
+		/*
+		 * For purposes of address bit routing, use power-of-2 math for
+		 * switch ports.
+		 */
+		if (!is_power_of_2(parent_iw))
+			parent_iw /= 3;
+	} else {
+		struct cxl_region_ref *parent_rr;
+		struct cxl_decoder *parent_cxld;
+
+		parent_rr = cxl_rr_load(parent_port, cxlr);
+		parent_cxld = parent_rr->decoder;
+		parent_ig = parent_cxld->interleave_granularity;
+		parent_iw = parent_cxld->interleave_ways;
+	}
+
+	granularity_to_cxl(parent_ig, &peig);
+	ways_to_cxl(parent_iw, &peiw);
+
+	iw = cxl_rr->nr_targets;
+	ways_to_cxl(iw, &eiw);
+	if (cxl_rr->nr_targets > 1) {
+		u32 address_bit = max(peig + peiw, eiw + peig);
+
+		eig = address_bit - eiw + 1;
+	} else {
+		eiw = peiw;
+		eig = peig;
+	}
+
+	rc = cxl_to_granularity(eig, &ig);
+	if (rc) {
+		dev_dbg(&cxlr->dev, "%s:%s: invalid interleave: %d\n",
+			dev_name(port->uport), dev_name(&port->dev),
+			256 << eig);
+		return rc;
+	}
+
+	cxld->interleave_ways = iw;
+	cxld->interleave_granularity = ig;
+	dev_dbg(&cxlr->dev, "%s:%s iw: %d ig: %d\n", dev_name(port->uport),
+		dev_name(&port->dev), iw, ig);
+add_target:
+	if (cxl_rr->nr_targets_set == cxl_rr->nr_targets) {
+		dev_dbg(&cxlr->dev,
+			"%s:%s: targets full trying to add %s:%s at %d\n",
+			dev_name(port->uport), dev_name(&port->dev),
+			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev), pos);
+		return -ENXIO;
+	}
+	cxlsd->target[cxl_rr->nr_targets_set] = ep->dport;
+	inc = 1;
+out_target_set:
+	cxl_rr->nr_targets_set += inc;
+	dev_dbg(&cxlr->dev, "%s:%s target[%d] = %s for %s:%s @ %d\n",
+		dev_name(port->uport), dev_name(&port->dev),
+		cxl_rr->nr_targets_set - 1, dev_name(ep->dport->dport),
+		dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev), pos);
+
+	return 0;
+}
+
+static void cxl_port_reset_targets(struct cxl_port *port,
+				   struct cxl_region *cxlr)
+{
+	struct cxl_region_ref *cxl_rr = cxl_rr_load(port, cxlr);
+
+	/*
+	 * After the last endpoint has been detached the entire cxl_rr may now
+	 * be gone.
+	 */
+	if (cxl_rr)
+		cxl_rr->nr_targets_set = 0;
+}
+
+static void cxl_region_teardown_targets(struct cxl_region *cxlr)
+{
+	struct cxl_region_params *p = &cxlr->params;
+	struct cxl_endpoint_decoder *cxled;
+	struct cxl_memdev *cxlmd;
+	struct cxl_port *iter;
+	struct cxl_ep *ep;
+	int i;
+
+	for (i = 0; i < p->nr_targets; i++) {
+		cxled = p->targets[i];
+		cxlmd = cxled_to_memdev(cxled);
+
+		iter = cxled_to_port(cxled);
+		while (!is_cxl_root(to_cxl_port(iter->dev.parent)))
+			iter = to_cxl_port(iter->dev.parent);
+
+		for (ep = cxl_ep_load(iter, cxlmd); iter;
+		     iter = ep->next, ep = cxl_ep_load(iter, cxlmd))
+			cxl_port_reset_targets(iter, cxlr);
+	}
+}
+
+static int cxl_region_setup_targets(struct cxl_region *cxlr)
+{
+	struct cxl_region_params *p = &cxlr->params;
+	struct cxl_endpoint_decoder *cxled;
+	struct cxl_memdev *cxlmd;
+	struct cxl_port *iter;
+	struct cxl_ep *ep;
+	int i, rc;
+
+	for (i = 0; i < p->nr_targets; i++) {
+		cxled = p->targets[i];
+		cxlmd = cxled_to_memdev(cxled);
+
+		iter = cxled_to_port(cxled);
+		while (!is_cxl_root(to_cxl_port(iter->dev.parent)))
+			iter = to_cxl_port(iter->dev.parent);
+
+		/*
+		 * Descend the topology tree programming targets while
+		 * looking for conflicts.
+		 */
+		for (ep = cxl_ep_load(iter, cxlmd); iter;
+		     iter = ep->next, ep = cxl_ep_load(iter, cxlmd)) {
+			rc = cxl_port_setup_targets(iter, cxlr, cxled);
+			if (rc) {
+				cxl_region_teardown_targets(cxlr);
+				return rc;
+			}
+		}
+	}
+
+	return 0;
 }
 
 static int cxl_region_attach(struct cxl_region *cxlr,
···
 	cxled->pos = pos;
 	p->nr_targets++;
 
-	if (p->nr_targets == p->interleave_ways)
+	if (p->nr_targets == p->interleave_ways) {
+		rc = cxl_region_setup_targets(cxlr);
+		if (rc)
+			goto err;
 		p->state = CXL_CONFIG_ACTIVE;
+	}
 
 	return 0;
 
···
 		goto out;
 	}
 
-	if (p->state == CXL_CONFIG_ACTIVE)
+	if (p->state == CXL_CONFIG_ACTIVE) {
 		p->state = CXL_CONFIG_INTERLEAVE_ACTIVE;
+		cxl_region_teardown_targets(cxlr);
+	}
 	p->targets[cxled->pos] = NULL;
 	p->nr_targets--;
 

drivers/cxl/cxl.h

···
  * @decoder: decoder assigned for @region in @port
  * @region: region for this reference
  * @endpoints: cxl_ep references for region members beneath @port
+ * @nr_targets_set: track how many targets have been programmed during setup
  * @nr_eps: number of endpoints beneath @port
  * @nr_targets: number of distinct targets needed to reach @nr_eps
  */
···
 	struct cxl_decoder *decoder;
 	struct cxl_region *region;
 	struct xarray endpoints;
+	int nr_targets_set;
 	int nr_eps;
 	int nr_targets;
 };