Merge branch 'for-6.3/cxl-ram-region' into cxl/next

Include the support for enumerating and provisioning ram regions for
v6.3. This also include a default policy change for ram / volatile
device-dax instances to assign them to the dax_kmem driver by default.

Documentation/ABI/testing/sysfs-bus-cxl

···
 
 What:		/sys/bus/cxl/devices/endpointX/CDAT
 Date:		July, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RO) If this sysfs entry is not present no DOE mailbox was
···
 
 What:		/sys/bus/cxl/devices/decoderX.Y/mode
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RW) When a CXL decoder is of devtype "cxl_decoder_endpoint" it
···
 
 What:		/sys/bus/cxl/devices/decoderX.Y/dpa_resource
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RO) When a CXL decoder is of devtype "cxl_decoder_endpoint",
···
 
 What:		/sys/bus/cxl/devices/decoderX.Y/dpa_size
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RW) When a CXL decoder is of devtype "cxl_decoder_endpoint" it
···
 
 What:		/sys/bus/cxl/devices/decoderX.Y/interleave_ways
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RO) The number of targets across which this decoder's host
···
 
 What:		/sys/bus/cxl/devices/decoderX.Y/interleave_granularity
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RO) The number of consecutive bytes of host physical address
···
 		interleave_granularity).
 
 
-What:		/sys/bus/cxl/devices/decoderX.Y/create_pmem_region
-Date:		May, 2022
-KernelVersion:	v5.20
+What:		/sys/bus/cxl/devices/decoderX.Y/create_{pmem,ram}_region
+Date:		May, 2022, January, 2023
+KernelVersion:	v6.0 (pmem), v6.3 (ram)
 Contact:	[e-mail]
 Description:
 		(RW) Write a string in the form 'regionZ' to start the process
-		of defining a new persistent memory region (interleave-set)
-		within the decode range bounded by root decoder 'decoderX.Y'.
-		The value written must match the current value returned from
-		reading this attribute. An atomic compare exchange operation is
-		done on write to assign the requested id to a region and
-		allocate the region-id for the next creation attempt. EBUSY is
-		returned if the region name written does not match the current
-		cached value.
+		of defining a new persistent, or volatile memory region
+		(interleave-set) within the decode range bounded by root decoder
+		'decoderX.Y'. The value written must match the current value
+		returned from reading this attribute. An atomic compare exchange
+		operation is done on write to assign the requested id to a
+		region and allocate the region-id for the next creation attempt.
+		EBUSY is returned if the region name written does not match the
+		current cached value.
 
 
 What:		/sys/bus/cxl/devices/decoderX.Y/delete_region
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(WO) Write a string in the form 'regionZ' to delete that region,
···
 
 What:		/sys/bus/cxl/devices/regionZ/uuid
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RW) Write a unique identifier for the region. This field must
 		be set for persistent regions and it must not conflict with the
-		UUID of another region.
+		UUID of another region. For volatile ram regions this
+		attribute is a read-only empty string.
 
 
 What:		/sys/bus/cxl/devices/regionZ/interleave_granularity
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RW) Set the number of consecutive bytes each device in the
···
 
 What:		/sys/bus/cxl/devices/regionZ/interleave_ways
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RW) Configures the number of devices participating in the
···
 
 What:		/sys/bus/cxl/devices/regionZ/size
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RW) System physical address space to be consumed by the region.
···
 		results in the same address being allocated.
 
 
+What:		/sys/bus/cxl/devices/regionZ/mode
+Date:		January, 2023
+KernelVersion:	v6.3
+Contact:	[e-mail]
+Description:
+		(RO) The mode of a region is established at region creation time
+		and dictates the mode of the endpoint decoder that comprise the
+		region. For more details on the possible modes see
+		/sys/bus/cxl/devices/decoderX.Y/mode
+
+
 What:		/sys/bus/cxl/devices/regionZ/resource
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RO) A region is a contiguous partition of a CXL root decoder
···
 
 What:		/sys/bus/cxl/devices/regionZ/target[0..N]
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RW) Write an endpoint decoder object name to 'targetX' where X
···
 
 What:		/sys/bus/cxl/devices/regionZ/commit
 Date:		May, 2022
-KernelVersion:	v5.20
+KernelVersion:	v6.0
 Contact:	[e-mail]
 Description:
 		(RW) Write a boolean 'true' string value to this attribute to

MAINTAINERS

···
 M:	Vishal Verma <[e-mail]>
 M:	Dave Jiang <[e-mail]>
 L:	[e-mail]
+L:	[e-mail]
 S:	Supported
 F:	drivers/dax/
 

drivers/acpi/numa/hmat.c

···
 	for (res = target->memregions.child; res; res = res->sibling) {
 		int target_nid = pxm_to_node(target->memory_pxm);
 
-		hmem_register_device(target_nid, res);
+		hmem_register_resource(target_nid, res);
 	}
 }
 
···
 	acpi_put_table(tbl);
 	return 0;
 }
-device_initcall(hmat_init);
+subsys_initcall(hmat_init);

drivers/cxl/Kconfig

···
 	depends on SUSPEND && CXL_MEM
 
 config CXL_REGION
-	bool
+	bool "CXL: Region Support"
 	default CXL_BUS
 	# For MAX_PHYSMEM_BITS
 	depends on SPARSEMEM
 	select MEMREGION
 	select GET_FREE_REGION
+	help
+	  Enable the CXL core to enumerate and provision CXL regions. A CXL
+	  region is defined by one or more CXL expanders that decode a given
+	  system-physical address range. For CXL regions established by
+	  platform-firmware this option enables memory error handling to
+	  identify the devices participating in a given interleaved memory
+	  range. Otherwise, platform-firmware managed CXL is enabled by being
+	  placed in the system address map and does not need a driver.
+
+	  If unsure say 'y'
 
 config CXL_REGION_INVALIDATION_TEST
 	bool "CXL: Region Cache Management Bypass (TEST)"

drivers/cxl/acpi.c

···
 	cxl_bus_drain();
 }
 
-module_init(cxl_acpi_init);
+/* load before dax_hmem sees 'Soft Reserved' CXL ranges */
+subsys_initcall(cxl_acpi_init);
 module_exit(cxl_acpi_exit);
 MODULE_LICENSE("GPL v2");
 MODULE_IMPORT_NS(CXL);

drivers/cxl/core/core.h

···
 
 #ifdef CONFIG_CXL_REGION
 extern struct device_attribute dev_attr_create_pmem_region;
+extern struct device_attribute dev_attr_create_ram_region;
 extern struct device_attribute dev_attr_delete_region;
 extern struct device_attribute dev_attr_region;
 extern const struct device_type cxl_pmem_region_type;
+extern const struct device_type cxl_dax_region_type;
 extern const struct device_type cxl_region_type;
 void cxl_decoder_kill_region(struct cxl_endpoint_decoder *cxled);
 #define CXL_REGION_ATTR(x) (&dev_attr_##x.attr)
 #define CXL_REGION_TYPE(x) (&cxl_region_type)
 #define SET_CXL_REGION_ATTR(x) (&dev_attr_##x.attr),
 #define CXL_PMEM_REGION_TYPE(x) (&cxl_pmem_region_type)
+#define CXL_DAX_REGION_TYPE(x) (&cxl_dax_region_type)
 int cxl_region_init(void);
 void cxl_region_exit(void);
 #else
···
 #define CXL_REGION_TYPE(x) NULL
 #define SET_CXL_REGION_ATTR(x)
 #define CXL_PMEM_REGION_TYPE(x) NULL
+#define CXL_DAX_REGION_TYPE(x) NULL
 #endif
 
 struct cxl_send_command;
···
 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);
-struct cxl_switch_decoder *to_cxl_switch_decoder(struct device *dev);
 
 int cxl_memdev_init(void);
 void cxl_memdev_exit(void);

drivers/cxl/core/hdm.c

···
 	return 0;
 }
 
-static int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
+int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 				resource_size_t base, resource_size_t len,
 				resource_size_t skipped)
 {
···
 
 	return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
 }
+EXPORT_SYMBOL_NS_GPL(devm_cxl_dpa_reserve, CXL);
 
 resource_size_t cxl_dpa_size(struct cxl_endpoint_decoder *cxled)
 {
···
 	port->commit_end--;
 	cxld->flags &= ~CXL_DECODER_F_ENABLE;
 
+	/* Userspace is now responsible for reconfiguring this decoder */
+	if (is_endpoint_decoder(&cxld->dev)) {
+		struct cxl_endpoint_decoder *cxled;
+
+		cxled = to_cxl_endpoint_decoder(&cxld->dev);
+		cxled->state = CXL_DECODER_STATE_MANUAL;
+	}
+
 	return 0;
 }
 
···
 		return rc;
 	}
 	*dpa_base += dpa_size + skip;
+
+	cxled->state = CXL_DECODER_STATE_AUTO;
+
 	return 0;
 }
 
···
 			cxled = cxl_endpoint_decoder_alloc(port);
 			if (IS_ERR(cxled)) {
 				dev_warn(&port->dev,
-					 "Failed to allocate the decoder\n");
+					 "Failed to allocate decoder%d.%d\n",
+					 port->id, i);
 				return PTR_ERR(cxled);
 			}
 			cxld = &cxled->cxld;
···
 			cxlsd = cxl_switch_decoder_alloc(port, target_count);
 			if (IS_ERR(cxlsd)) {
 				dev_warn(&port->dev,
-					 "Failed to allocate the decoder\n");
+					 "Failed to allocate decoder%d.%d\n",
+					 port->id, i);
 				return PTR_ERR(cxlsd);
 			}
 			cxld = &cxlsd->cxld;
···
 
 		rc = init_hdm_decoder(port, cxld, target_map, hdm, i, &dpa_base);
 		if (rc) {
+			dev_warn(&port->dev,
+				 "Failed to initialize decoder%d.%d\n",
+				 port->id, i);
 			put_device(&cxld->dev);
 			return rc;
 		}
 		rc = add_hdm_decoder(port, cxld, target_map);
 		if (rc) {
 			dev_warn(&port->dev,
-				 "Failed to add decoder to port\n");
+				 "Failed to add decoder%d.%d\n", port->id, i);
 			return rc;
 		}
 	}

drivers/cxl/core/memdev.c

···
 	if (rc < 0)
 		goto err;
 	cxlmd->id = rc;
+	cxlmd->depth = -1;
 
 	dev = &cxlmd->dev;
 	device_initialize(dev);

drivers/cxl/core/pci.c

···
 	return devm_add_action_or_reset(host, clear_mem_enable, cxlds);
 }
 
-static bool range_contains(struct range *r1, struct range *r2)
-{
-	return r1->start <= r2->start && r1->end >= r2->end;
-}
-
 /* require dvsec ranges to be covered by a locked platform window */
 static int dvsec_range_allowed(struct device *dev, void *arg)
 {

drivers/cxl/core/port.c

···
 		return CXL_DEVICE_NVDIMM;
 	if (dev->type == CXL_PMEM_REGION_TYPE())
 		return CXL_DEVICE_PMEM_REGION;
+	if (dev->type == CXL_DAX_REGION_TYPE())
+		return CXL_DEVICE_DAX_REGION;
 	if (is_cxl_port(dev)) {
 		if (is_cxl_root(to_cxl_port(dev)))
 			return CXL_DEVICE_ROOT;
···
 {
 	struct cxl_endpoint_decoder *cxled = to_cxl_endpoint_decoder(dev);
 
-	switch (cxled->mode) {
-	case CXL_DECODER_RAM:
-		return sysfs_emit(buf, "ram\n");
-	case CXL_DECODER_PMEM:
-		return sysfs_emit(buf, "pmem\n");
-	case CXL_DECODER_NONE:
-		return sysfs_emit(buf, "none\n");
-	case CXL_DECODER_MIXED:
-	default:
-		return sysfs_emit(buf, "mixed\n");
-	}
+	return sysfs_emit(buf, "%s\n", cxl_decoder_mode_name(cxled->mode));
 }
 
 static ssize_t mode_store(struct device *dev, struct device_attribute *attr,
···
 	&dev_attr_cap_type3.attr,
 	&dev_attr_target_list.attr,
 	SET_CXL_REGION_ATTR(create_pmem_region)
+	SET_CXL_REGION_ATTR(create_ram_region)
 	SET_CXL_REGION_ATTR(delete_region)
 	NULL,
 };
···
 static bool can_create_pmem(struct cxl_root_decoder *cxlrd)
 {
 	unsigned long flags = CXL_DECODER_F_TYPE3 | CXL_DECODER_F_PMEM;
+
+	return (cxlrd->cxlsd.cxld.flags & flags) == flags;
+}
+
+static bool can_create_ram(struct cxl_root_decoder *cxlrd)
+{
+	unsigned long flags = CXL_DECODER_F_TYPE3 | CXL_DECODER_F_RAM;
 
 	return (cxlrd->cxlsd.cxld.flags & flags) == flags;
 }
···
 	if (a == CXL_REGION_ATTR(create_pmem_region) && !can_create_pmem(cxlrd))
 		return 0;
 
-	if (a == CXL_REGION_ATTR(delete_region) && !can_create_pmem(cxlrd))
+	if (a == CXL_REGION_ATTR(create_ram_region) && !can_create_ram(cxlrd))
+		return 0;
+
+	if (a == CXL_REGION_ATTR(delete_region) &&
+	    !(can_create_pmem(cxlrd) || can_create_ram(cxlrd)))
 		return 0;
 
 	return a->mode;
···
 {
 	return dev->type == &cxl_decoder_endpoint_type;
 }
+EXPORT_SYMBOL_NS_GPL(is_endpoint_decoder, CXL);
 
 bool is_root_decoder(struct device *dev)
 {
···
 {
 	return is_root_decoder(dev) || dev->type == &cxl_decoder_switch_type;
 }
+EXPORT_SYMBOL_NS_GPL(is_switch_decoder, CXL);
 
 struct cxl_decoder *to_cxl_decoder(struct device *dev)
 {
···
 		return NULL;
 	return container_of(dev, struct cxl_switch_decoder, cxld.dev);
 }
+EXPORT_SYMBOL_NS_GPL(to_cxl_switch_decoder, CXL);
 
 static void cxl_ep_release(struct cxl_ep *ep)
 {
···
 
 	get_device(&endpoint->dev);
 	dev_set_drvdata(dev, endpoint);
+	cxlmd->depth = endpoint->depth;
 	return devm_add_action_or_reset(dev, delete_endpoint, cxlmd);
 }
 EXPORT_SYMBOL_NS_GPL(cxl_endpoint_autoremove, CXL);
···
 	}
 }
 
+struct detach_ctx {
+	struct cxl_memdev *cxlmd;
+	int depth;
+};
+
+static int port_has_memdev(struct device *dev, const void *data)
+{
+	const struct detach_ctx *ctx = data;
+	struct cxl_port *port;
+
+	if (!is_cxl_port(dev))
+		return 0;
+
+	port = to_cxl_port(dev);
+	if (port->depth != ctx->depth)
+		return 0;
+
+	return !!cxl_ep_load(port, ctx->cxlmd);
+}
+
 static void cxl_detach_ep(void *data)
 {
 	struct cxl_memdev *cxlmd = data;
-	struct device *iter;
 
-	for (iter = &cxlmd->dev; iter; iter = grandparent(iter)) {
-		struct device *dport_dev = grandparent(iter);
+	for (int i = cxlmd->depth - 1; i >= 1; i--) {
 		struct cxl_port *port, *parent_port;
+		struct detach_ctx ctx = {
+			.cxlmd = cxlmd,
+			.depth = i,
+		};
+		struct device *dev;
 		struct cxl_ep *ep;
 		bool died = false;
 
-		if (!dport_dev)
-			break;
-
-		port = find_cxl_port(dport_dev, NULL);
-		if (!port)
+		dev = bus_find_device(&cxl_bus_type, NULL, &ctx,
+				      port_has_memdev);
+		if (!dev)
 			continue;
-
-		if (is_cxl_root(port)) {
-			put_device(&port->dev);
-			continue;
-		}
+		port = to_cxl_port(dev);
 
 		parent_port = to_cxl_port(port->dev.parent);
 		device_lock(&parent_port->dev);
-		if (!parent_port->dev.driver) {
-			/*
-			 * The bottom-up race to delete the port lost to a
-			 * top-down port disable, give up here, because the
-			 * parent_port ->remove() will have cleaned up all
-			 * descendants.
-			 */
-			device_unlock(&parent_port->dev);
-			put_device(&port->dev);
-			continue;
-		}
-
 		device_lock(&port->dev);
 		ep = cxl_ep_load(port, cxlmd);
 		dev_dbg(&cxlmd->dev, "disconnect %s from %s\n",
 			ep ? dev_name(ep->ep) : "", dev_name(&port->dev));
 		cxl_ep_remove(port, ep);
 		if (ep && !port->dead && xa_empty(&port->endpoints) &&
-		    !is_cxl_root(parent_port)) {
+		    !is_cxl_root(parent_port) && parent_port->dev.driver) {
 			/*
 			 * This was the last ep attached to a dynamically
 			 * enumerated port. Block new cxl_add_ep() and garbage
···
 	}
 
 	cxlrd->calc_hb = calc_hb;
+	mutex_init(&cxlrd->range_lock);
 
 	cxld = &cxlsd->cxld;
 	cxld->dev.type = &cxl_decoder_root_type;
···
 	debugfs_remove_recursive(cxl_debugfs);
 }
 
-module_init(cxl_core_init);
+subsys_initcall(cxl_core_init);
 module_exit(cxl_core_exit);
 MODULE_LICENSE("GPL v2");

drivers/cxl/core/region.c

···
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/uuid.h>
+#include <linux/sort.h>
 #include <linux/idr.h>
 #include <cxlmem.h>
 #include <cxl.h>
···
 	rc = down_read_interruptible(&cxl_region_rwsem);
 	if (rc)
 		return rc;
-	rc = sysfs_emit(buf, "%pUb\n", &p->uuid);
+	if (cxlr->mode != CXL_DECODER_PMEM)
+		rc = sysfs_emit(buf, "\n");
+	else
+		rc = sysfs_emit(buf, "%pUb\n", &p->uuid);
 	up_read(&cxl_region_rwsem);
 
 	return rc;
···
 	struct device *dev = kobj_to_dev(kobj);
 	struct cxl_region *cxlr = to_cxl_region(dev);
 
+	/*
+	 * Support tooling that expects to find a 'uuid' attribute for all
+	 * regions regardless of mode.
+	 */
 	if (a == &dev_attr_uuid.attr && cxlr->mode != CXL_DECODER_PMEM)
-		return 0;
+		return 0444;
 	return a->mode;
 }
 
···
 }
 static DEVICE_ATTR_RO(resource);
 
+static ssize_t mode_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct cxl_region *cxlr = to_cxl_region(dev);
+
+	return sysfs_emit(buf, "%s\n", cxl_decoder_mode_name(cxlr->mode));
+}
+static DEVICE_ATTR_RO(mode);
+
 static int alloc_hpa(struct cxl_region *cxlr, resource_size_t size)
 {
 	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
···
 	if (device_is_registered(&cxlr->dev))
 		lockdep_assert_held_write(&cxl_region_rwsem);
 	if (p->res) {
-		remove_resource(p->res);
+		/*
+		 * Autodiscovered regions may not have been able to insert their
+		 * resource.
+		 */
+		if (p->res->parent)
+			remove_resource(p->res);
 		kfree(p->res);
 		p->res = NULL;
 	}
···
 	&dev_attr_interleave_granularity.attr,
 	&dev_attr_resource.attr,
 	&dev_attr_size.attr,
+	&dev_attr_mode.attr,
 	NULL,
 };
 
···
 		return rc;
 	}
 
-	cxld->interleave_ways = iw;
-	cxld->interleave_granularity = ig;
-	cxld->hpa_range = (struct range) {
-		.start = p->res->start,
-		.end = p->res->end,
-	};
+	if (test_bit(CXL_REGION_F_AUTO, &cxlr->flags)) {
+		if (cxld->interleave_ways != iw ||
+		    cxld->interleave_granularity != ig ||
+		    cxld->hpa_range.start != p->res->start ||
+		    cxld->hpa_range.end != p->res->end ||
+		    ((cxld->flags & CXL_DECODER_F_ENABLE) == 0)) {
+			dev_err(&cxlr->dev,
+				"%s:%s %s expected iw: %d ig: %d %pr\n",
+				dev_name(port->uport), dev_name(&port->dev),
+				__func__, iw, ig, p->res);
+			dev_err(&cxlr->dev,
+				"%s:%s %s got iw: %d ig: %d state: %s %#llx:%#llx\n",
+				dev_name(port->uport), dev_name(&port->dev),
+				__func__, cxld->interleave_ways,
+				cxld->interleave_granularity,
+				(cxld->flags & CXL_DECODER_F_ENABLE) ?
+					"enabled" :
+					"disabled",
+				cxld->hpa_range.start, cxld->hpa_range.end);
+			return -ENXIO;
+		}
+	} else {
+		cxld->interleave_ways = iw;
+		cxld->interleave_granularity = ig;
+		cxld->hpa_range = (struct range) {
+			.start = p->res->start,
+			.end = p->res->end,
+		};
+	}
 	dev_dbg(&cxlr->dev, "%s:%s iw: %d ig: %d\n", dev_name(port->uport),
 		dev_name(&port->dev), iw, ig);
 add_target:
···
 			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev), pos);
 		return -ENXIO;
 	}
-	cxlsd->target[cxl_rr->nr_targets_set] = ep->dport;
+	if (test_bit(CXL_REGION_F_AUTO, &cxlr->flags)) {
+		if (cxlsd->target[cxl_rr->nr_targets_set] != ep->dport) {
+			dev_dbg(&cxlr->dev, "%s:%s: %s expected %s at %d\n",
+				dev_name(port->uport), dev_name(&port->dev),
+				dev_name(&cxlsd->cxld.dev),
+				dev_name(ep->dport->dport),
+				cxl_rr->nr_targets_set);
+			return -ENXIO;
+		}
+	} else
+		cxlsd->target[cxl_rr->nr_targets_set] = ep->dport;
 	inc = 1;
 out_target_set:
 	cxl_rr->nr_targets_set += inc;
···
 	struct cxl_ep *ep;
 	int i;
 
+	/*
+	 * In the auto-discovery case skip automatic teardown since the
+	 * address space is already active
+	 */
+	if (test_bit(CXL_REGION_F_AUTO, &cxlr->flags))
+		return;
+
 	for (i = 0; i < p->nr_targets; i++) {
 		cxled = p->targets[i];
 		cxlmd = cxled_to_memdev(cxled);
···
 			iter = to_cxl_port(iter->dev.parent);
 
 		/*
-		 * Descend the topology tree programming targets while
-		 * looking for conflicts.
+		 * Descend the topology tree programming / validating
+		 * targets while looking for conflicts.
 		 */
 		for (ep = cxl_ep_load(iter, cxlmd); iter;
 		     iter = ep->next, ep = cxl_ep_load(iter, cxlmd)) {
···
 	return 0;
 }
 
-static int cxl_region_attach(struct cxl_region *cxlr,
-			     struct cxl_endpoint_decoder *cxled, int pos)
+static int cxl_region_validate_position(struct cxl_region *cxlr,
+					struct cxl_endpoint_decoder *cxled,
+					int pos)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
 	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
-	struct cxl_port *ep_port, *root_port, *iter;
 	struct cxl_region_params *p = &cxlr->params;
-	struct cxl_dport *dport;
-	int i, rc = -ENXIO;
-
-	if (cxled->mode == CXL_DECODER_DEAD) {
-		dev_dbg(&cxlr->dev, "%s dead\n", dev_name(&cxled->cxld.dev));
-		return -ENODEV;
-	}
-
-	/* all full of members, or interleave config not established? */
-	if (p->state > CXL_CONFIG_INTERLEAVE_ACTIVE) {
-		dev_dbg(&cxlr->dev, "region already active\n");
-		return -EBUSY;
-	} else if (p->state < CXL_CONFIG_INTERLEAVE_ACTIVE) {
-		dev_dbg(&cxlr->dev, "interleave config missing\n");
-		return -ENXIO;
-	}
+	int i;
 
 	if (pos < 0 || pos >= p->interleave_ways) {
 		dev_dbg(&cxlr->dev, "position %d out of range %d\n", pos,
···
 		}
 	}
 
+	return 0;
+}
+
+static int cxl_region_attach_position(struct cxl_region *cxlr,
+				      struct cxl_root_decoder *cxlrd,
+				      struct cxl_endpoint_decoder *cxled,
+				      const struct cxl_dport *dport, int pos)
+{
+	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
+	struct cxl_port *iter;
+	int rc;
+
+	if (cxlrd->calc_hb(cxlrd, pos) != dport) {
+		dev_dbg(&cxlr->dev, "%s:%s invalid target position for %s\n",
+			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
+			dev_name(&cxlrd->cxlsd.cxld.dev));
+		return -ENXIO;
+	}
+
+	for (iter = cxled_to_port(cxled); !is_cxl_root(iter);
+	     iter = to_cxl_port(iter->dev.parent)) {
+		rc = cxl_port_attach_region(iter, cxlr, cxled, pos);
+		if (rc)
+			goto err;
+	}
+
+	return 0;
+
+err:
+	for (iter = cxled_to_port(cxled); !is_cxl_root(iter);
+	     iter = to_cxl_port(iter->dev.parent))
+		cxl_port_detach_region(iter, cxlr, cxled);
+	return rc;
+}
+
+static int cxl_region_attach_auto(struct cxl_region *cxlr,
+				  struct cxl_endpoint_decoder *cxled, int pos)
+{
+	struct cxl_region_params *p = &cxlr->params;
+
+	if (cxled->state != CXL_DECODER_STATE_AUTO) {
+		dev_err(&cxlr->dev,
+			"%s: unable to add decoder to autodetected region\n",
+			dev_name(&cxled->cxld.dev));
+		return -EINVAL;
+	}
+
+	if (pos >= 0) {
+		dev_dbg(&cxlr->dev, "%s: expected auto position, not %d\n",
+			dev_name(&cxled->cxld.dev), pos);
+		return -EINVAL;
+	}
+
+	if (p->nr_targets >= p->interleave_ways) {
+		dev_err(&cxlr->dev, "%s: no more target slots available\n",
+			dev_name(&cxled->cxld.dev));
+		return -ENXIO;
+	}
+
+	/*
+	 * Temporarily record the endpoint decoder into the target array. Yes,
+	 * this means that userspace can view devices in the wrong position
+	 * before the region activates, and must be careful to understand when
+	 * it might be racing region autodiscovery.
+	 */
+	pos = p->nr_targets;
+	p->targets[pos] = cxled;
+	cxled->pos = pos;
+	p->nr_targets++;
+
+	return 0;
+}
+
+static struct cxl_port *next_port(struct cxl_port *port)
+{
+	if (!port->parent_dport)
+		return NULL;
+	return port->parent_dport->port;
+}
+
+static int decoder_match_range(struct device *dev, void *data)
+{
+	struct cxl_endpoint_decoder *cxled = data;
+	struct cxl_switch_decoder *cxlsd;
+
+	if (!is_switch_decoder(dev))
+		return 0;
+
+	cxlsd = to_cxl_switch_decoder(dev);
+	return range_contains(&cxlsd->cxld.hpa_range, &cxled->cxld.hpa_range);
+}
+
+static void find_positions(const struct cxl_switch_decoder *cxlsd,
+			   const struct cxl_port *iter_a,
+			   const struct cxl_port *iter_b, int *a_pos,
+			   int *b_pos)
+{
+	int i;
+
+	for (i = 0, *a_pos = -1, *b_pos = -1; i < cxlsd->nr_targets; i++) {
+		if (cxlsd->target[i] == iter_a->parent_dport)
+			*a_pos = i;
+		else if (cxlsd->target[i] == iter_b->parent_dport)
+			*b_pos = i;
+		if (*a_pos >= 0 && *b_pos >= 0)
+			break;
+	}
+}
+
+static int cmp_decode_pos(const void *a, const void *b)
+{
+	struct cxl_endpoint_decoder *cxled_a = *(typeof(cxled_a) *)a;
+	struct cxl_endpoint_decoder *cxled_b = *(typeof(cxled_b) *)b;
+	struct cxl_memdev *cxlmd_a = cxled_to_memdev(cxled_a);
+	struct cxl_memdev *cxlmd_b = cxled_to_memdev(cxled_b);
+	struct cxl_port *port_a = cxled_to_port(cxled_a);
+	struct cxl_port *port_b = cxled_to_port(cxled_b);
+	struct cxl_port *iter_a, *iter_b, *port = NULL;
+	struct cxl_switch_decoder *cxlsd;
+	struct device *dev;
+	int a_pos, b_pos;
+	unsigned int seq;
+
+	/* Exit early if any prior sorting failed */
+	if (cxled_a->pos < 0 || cxled_b->pos < 0)
+		return 0;
+
+	/*
+	 * Walk up the hierarchy to find a shared port, find the decoder that
+	 * maps the range, compare the relative position of those dport
+	 * mappings.
+	 */
+	for (iter_a = port_a; iter_a; iter_a = next_port(iter_a)) {
+		struct cxl_port *next_a, *next_b;
+
+		next_a = next_port(iter_a);
+		if (!next_a)
+			break;
+
+		for (iter_b = port_b; iter_b; iter_b = next_port(iter_b)) {
+			next_b = next_port(iter_b);
+			if (next_a != next_b)
+				continue;
+			port = next_a;
+			break;
+		}
+
+		if (port)
+			break;
+	}
+
+	if (!port) {
+		dev_err(cxlmd_a->dev.parent,
+			"failed to find shared port with %s\n",
+			dev_name(cxlmd_b->dev.parent));
+		goto err;
+	}
+
+	dev = device_find_child(&port->dev, cxled_a, decoder_match_range);
+	if (!dev) {
+		struct range *range = &cxled_a->cxld.hpa_range;
+
+		dev_err(port->uport,
+			"failed to find decoder that maps %#llx-%#llx\n",
+			range->start, range->end);
+		goto err;
+	}
+
+	cxlsd = to_cxl_switch_decoder(dev);
+	do {
+		seq = read_seqbegin(&cxlsd->target_lock);
+		find_positions(cxlsd, iter_a, iter_b, &a_pos, &b_pos);
+	} while (read_seqretry(&cxlsd->target_lock, seq));
+
+	put_device(dev);
+
+	if (a_pos < 0 || b_pos < 0) {
+		dev_err(port->uport,
+			"failed to find shared decoder for %s and %s\n",
+			dev_name(cxlmd_a->dev.parent),
+			dev_name(cxlmd_b->dev.parent));
+		goto err;
+	}
+
+	dev_dbg(port->uport, "%s comes %s %s\n", dev_name(cxlmd_a->dev.parent),
+		a_pos - b_pos < 0 ? "before" : "after",
+		dev_name(cxlmd_b->dev.parent));
+
+	return a_pos - b_pos;
+err:
+	cxled_a->pos = -1;
+	return 0;
+}
+
+static int cxl_region_sort_targets(struct cxl_region *cxlr)
+{
+	struct cxl_region_params *p = &cxlr->params;
+	int i, rc = 0;
+
+	sort(p->targets, p->nr_targets, sizeof(p->targets[0]), cmp_decode_pos,
+	     NULL);
+
+	for (i = 0; i < p->nr_targets; i++) {
+		struct cxl_endpoint_decoder *cxled = p->targets[i];
+
+		/*
+		 * Record that sorting failed, but still continue to restore
+		 * cxled->pos with its ->targets[] position so that follow-on
+		 * code paths can reliably do p->targets[cxled->pos] to
+		 * self-reference their entry.
+		 */
+		if (cxled->pos < 0)
+			rc = -ENXIO;
+		cxled->pos = i;
+	}
+
+	dev_dbg(&cxlr->dev, "region sort %s\n", rc ? "failed" : "successful");
+	return rc;
+}
+
+static int cxl_region_attach(struct cxl_region *cxlr,
+			     struct cxl_endpoint_decoder *cxled, int pos)
+{
+	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(cxlr->dev.parent);
+	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
+	struct cxl_region_params *p = &cxlr->params;
+	struct cxl_port *ep_port, *root_port;
+	struct cxl_dport *dport;
+	int rc = -ENXIO;
+
+	if (cxled->mode != cxlr->mode) {
+		dev_dbg(&cxlr->dev, "%s region mode: %d mismatch: %d\n",
+			dev_name(&cxled->cxld.dev), cxlr->mode, cxled->mode);
+		return -EINVAL;
+	}
+
+	if (cxled->mode == CXL_DECODER_DEAD) {
+		dev_dbg(&cxlr->dev, "%s dead\n", dev_name(&cxled->cxld.dev));
+		return -ENODEV;
+	}
+
+	/* all full of members, or interleave config not established? */
+	if (p->state > CXL_CONFIG_INTERLEAVE_ACTIVE) {
+		dev_dbg(&cxlr->dev, "region already active\n");
+		return -EBUSY;
+	} else if (p->state < CXL_CONFIG_INTERLEAVE_ACTIVE) {
+		dev_dbg(&cxlr->dev, "interleave config missing\n");
+		return -ENXIO;
+	}
+
 	ep_port = cxled_to_port(cxled);
 	root_port = cxlrd_to_port(cxlrd);
 	dport = cxl_find_dport_by_dev(root_port, ep_port->host_bridge);
···
 		dev_dbg(&cxlr->dev, "%s:%s invalid target for %s\n",
 			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
 			dev_name(cxlr->dev.parent));
-		return -ENXIO;
-	}
-
-	if (cxlrd->calc_hb(cxlrd, pos) != dport) {
-		dev_dbg(&cxlr->dev, "%s:%s invalid target position for %s\n",
-			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
-			dev_name(&cxlrd->cxlsd.cxld.dev));
 		return -ENXIO;
 	}
 
···
 		return -EINVAL;
 	}
 
-	for (iter = ep_port; !is_cxl_root(iter);
-	     iter = to_cxl_port(iter->dev.parent)) {
-		rc = cxl_port_attach_region(iter, cxlr, cxled, pos);
+	if (test_bit(CXL_REGION_F_AUTO, &cxlr->flags)) {
+		int i;
+
+		rc = cxl_region_attach_auto(cxlr, cxled, pos);
 		if (rc)
-			goto err;
+			return rc;
+
+		/* await more targets to arrive... */
+		if (p->nr_targets < p->interleave_ways)
+			return 0;
+
+		/*
+		 * All targets are here, which implies all PCI enumeration that
+		 * affects this region has been completed. Walk the topology to
+		 * sort the devices into their relative region decode position.
+		 */
+		rc = cxl_region_sort_targets(cxlr);
+		if (rc)
+			return rc;
+
+		for (i = 0; i < p->nr_targets; i++) {
+			cxled = p->targets[i];
+			ep_port = cxled_to_port(cxled);
+			dport = cxl_find_dport_by_dev(root_port,
+						      ep_port->host_bridge);
+			rc = cxl_region_attach_position(cxlr, cxlrd, cxled,
+							dport, i);
+			if (rc)
+				return rc;
+		}
+
+		rc = cxl_region_setup_targets(cxlr);
+		if (rc)
+			return rc;
+
+		/*
+		 * If target setup succeeds in the autodiscovery case
+		 * then the region is already committed.
+		 */
+		p->state = CXL_CONFIG_COMMIT;
+
+		return 0;
 	}
+
+	rc = cxl_region_validate_position(cxlr, cxled, pos);
+	if (rc)
+		return rc;
+
+	rc = cxl_region_attach_position(cxlr, cxlrd, cxled, dport, pos);
+	if (rc)
+		return rc;
 
 	p->targets[pos] = cxled;
 	cxled->pos = pos;
···
 
 err_decrement:
 	p->nr_targets--;
-err:
-	for (iter = ep_port; !is_cxl_root(iter);
-	     iter = to_cxl_port(iter->dev.parent))
-		cxl_port_detach_region(iter, cxlr, cxled);
+	cxled->pos = -1;
+	p->targets[pos] = NULL;
 	return rc;
 }
 
···
 	up_write(&cxl_region_rwsem);
 }
 
-static int attach_target(struct cxl_region *cxlr, const char *decoder, int pos)
+static int attach_target(struct cxl_region *cxlr,
+			 struct cxl_endpoint_decoder *cxled, int pos,
+			 unsigned int state)
 {
-	struct device *dev;
-	int rc;
+	int rc = 0;
 
-	dev = bus_find_device_by_name(&cxl_bus_type, NULL, decoder);
-	if (!dev)
-		return -ENODEV;
-
-	if (!is_endpoint_decoder(dev)) {
-		put_device(dev);
-		return -EINVAL;
-	}
-
-	rc = down_write_killable(&cxl_region_rwsem);
+	if (state == TASK_INTERRUPTIBLE)
+		rc = down_write_killable(&cxl_region_rwsem);
+	else
+		down_write(&cxl_region_rwsem);
 	if (rc)
-		goto out;
+		return rc;
+
 	down_read(&cxl_dpa_rwsem);
-	rc = cxl_region_attach(cxlr, to_cxl_endpoint_decoder(dev), pos);
+	rc = cxl_region_attach(cxlr, cxled, pos);
 	if (rc == 0)
 		set_bit(CXL_REGION_F_INCOHERENT, &cxlr->flags);
 	up_read(&cxl_dpa_rwsem);
 	up_write(&cxl_region_rwsem);
-out:
-	put_device(dev);
 	return rc;
 }
 
···
 
 	if (sysfs_streq(buf, "\n"))
 		rc = detach_target(cxlr, pos);
-	else
-		rc = attach_target(cxlr, buf, pos);
+	else {
+		struct device *dev;
+
+		dev = bus_find_device_by_name(&cxl_bus_type, NULL, buf);
+		if (!dev)
+			return -ENODEV;
+
+		if (!is_endpoint_decoder(dev)) {
+			rc = -EINVAL;
+			goto out;
+		}
+
+		rc = attach_target(cxlr, to_cxl_endpoint_decoder(dev), pos,
+				   TASK_INTERRUPTIBLE);
+out:
+		put_device(dev);
+	}
 
 	if (rc < 0)
 		return rc;
···
 	struct device *dev;
 	int rc;
 
+	switch (mode) {
+	case CXL_DECODER_RAM:
+	case CXL_DECODER_PMEM:
+		break;
+	default:
+		dev_err(&cxlrd->cxlsd.cxld.dev, "unsupported mode %d\n", mode);
+		return ERR_PTR(-EINVAL);
+	}
+
 	cxlr = cxl_region_alloc(cxlrd, id);
 	if (IS_ERR(cxlr))
 		return cxlr;
···
 	return ERR_PTR(rc);
 }
 
+static ssize_t __create_region_show(struct cxl_root_decoder *cxlrd, char *buf)
+{
+	return sysfs_emit(buf, "region%u\n", atomic_read(&cxlrd->region_id));
+}
+
 static ssize_t create_pmem_region_show(struct device *dev,
 				       struct device_attribute *attr, char *buf)
 {
-	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev);
+	return __create_region_show(to_cxl_root_decoder(dev), buf);
+}
 
-	return sysfs_emit(buf, "region%u\n", atomic_read(&cxlrd->region_id));
+static ssize_t create_ram_region_show(struct device *dev,
+				      struct device_attribute *attr, char *buf)
+{
+	return __create_region_show(to_cxl_root_decoder(dev), buf);
+}
+
+static struct cxl_region *__create_region(struct cxl_root_decoder *cxlrd,
+					  enum cxl_decoder_mode mode, int id)
+{
+	int rc;
+
+	rc = memregion_alloc(GFP_KERNEL);
+	if (rc < 0)
+		return ERR_PTR(rc);
+
+	if (atomic_cmpxchg(&cxlrd->region_id, id, rc) != id) {
+		memregion_free(rc);
+		return ERR_PTR(-EBUSY);
+	}
+
+	return devm_cxl_add_region(cxlrd, id, mode, CXL_DECODER_EXPANDER);
 }
 
 static ssize_t create_pmem_region_store(struct device *dev,
···
 {
 	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev);
 	struct cxl_region *cxlr;
-	int id, rc;
+	int rc, id;
 
 	rc = sscanf(buf, "region%d\n", &id);
 	if (rc != 1)
 		return -EINVAL;
 
-	rc = memregion_alloc(GFP_KERNEL);
-	if (rc < 0)
-		return rc;
-
-	if (atomic_cmpxchg(&cxlrd->region_id, id, rc) != id) {
-		memregion_free(rc);
-		return -EBUSY;
-	}
-
-	cxlr = devm_cxl_add_region(cxlrd, id, CXL_DECODER_PMEM,
-				   CXL_DECODER_EXPANDER);
+	cxlr = __create_region(cxlrd, CXL_DECODER_PMEM, id);
 	if (IS_ERR(cxlr))
 		return PTR_ERR(cxlr);
 
 	return len;
 }
 DEVICE_ATTR_RW(create_pmem_region);
+
+static ssize_t create_ram_region_store(struct device *dev,
+				       struct device_attribute *attr,
+				       const char *buf, size_t len)
+{
+	struct cxl_root_decoder *cxlrd = to_cxl_root_decoder(dev);
+	struct cxl_region *cxlr;
+	int rc, id;
+
+	rc = sscanf(buf, "region%d\n", &id);
+	if (rc != 1)
+		return -EINVAL;
+
+	cxlr = __create_region(cxlrd, CXL_DECODER_RAM, id);
+	if (IS_ERR(cxlr))
+		return PTR_ERR(cxlr);
+
+	return len;
+}
+DEVICE_ATTR_RW(create_ram_region);
 
 static ssize_t region_show(struct device *dev, struct device_attribute *attr,
 			   char *buf)
···
 	return cxlr_pmem;
 }
 
+static void cxl_dax_region_release(struct device *dev)
+{
+	struct cxl_dax_region *cxlr_dax = to_cxl_dax_region(dev);
+
+	kfree(cxlr_dax);
+}
+
+static const struct attribute_group *cxl_dax_region_attribute_groups[] = {
+	&cxl_base_attribute_group,
+	NULL,
+};
+
+const struct device_type cxl_dax_region_type = {
+	.name = "cxl_dax_region",
+	.release = cxl_dax_region_release,
+	.groups = cxl_dax_region_attribute_groups,
+};
+
+static bool is_cxl_dax_region(struct device *dev)
+{
+	return dev->type == &cxl_dax_region_type;
+}
+
+struct cxl_dax_region *to_cxl_dax_region(struct device *dev)
+{
+	if (dev_WARN_ONCE(dev, !is_cxl_dax_region(dev),
+			  "not a cxl_dax_region device\n"))
+		return NULL;
+	return container_of(dev, struct cxl_dax_region, dev);
+}
+EXPORT_SYMBOL_NS_GPL(to_cxl_dax_region, CXL);
+
+static struct lock_class_key cxl_dax_region_key;
+
+static struct cxl_dax_region *cxl_dax_region_alloc(struct cxl_region *cxlr)
+{
+	struct cxl_region_params *p = &cxlr->params;
+	struct cxl_dax_region *cxlr_dax;
+	struct device *dev;
+
+	down_read(&cxl_region_rwsem);
+	if (p->state != CXL_CONFIG_COMMIT) {
+		cxlr_dax = ERR_PTR(-ENXIO);
+		goto out;
+	}
+
+	cxlr_dax = kzalloc(sizeof(*cxlr_dax), GFP_KERNEL);
+	if (!cxlr_dax) {
+		cxlr_dax = ERR_PTR(-ENOMEM);
+		goto out;
+	}
+
+	cxlr_dax->hpa_range.start = p->res->start;
+	cxlr_dax->hpa_range.end = p->res->end;
+
+	dev = &cxlr_dax->dev;
+	cxlr_dax->cxlr = cxlr;
+	device_initialize(dev);
+	lockdep_set_class(&dev->mutex, &cxl_dax_region_key);
+	device_set_pm_not_required(dev);
+	dev->parent = &cxlr->dev;
+	dev->bus = &cxl_bus_type;
+	dev->type = &cxl_dax_region_type;
+out:
+	up_read(&cxl_region_rwsem);
+
+	return cxlr_dax;
+}
+
 static void cxlr_pmem_unregister(void *_cxlr_pmem)
 {
 	struct cxl_pmem_region *cxlr_pmem = _cxlr_pmem;
···
 	return rc;
 }
 
+static void cxlr_dax_unregister(void *_cxlr_dax)
+{
+	struct cxl_dax_region *cxlr_dax = _cxlr_dax;
+
+	device_unregister(&cxlr_dax->dev);
+}
+
+static int devm_cxl_add_dax_region(struct cxl_region *cxlr)
+{
+	struct cxl_dax_region *cxlr_dax;
+	struct device *dev;
+	int rc;
+
+	cxlr_dax = cxl_dax_region_alloc(cxlr);
+	if (IS_ERR(cxlr_dax))
+		return PTR_ERR(cxlr_dax);
+
+	dev = &cxlr_dax->dev;
+	rc = dev_set_name(dev, "dax_region%d", cxlr->id);
+	if (rc)
+		goto err;
+
+	rc = device_add(dev);
+	if (rc)
+		goto err;
+
+	dev_dbg(&cxlr->dev, "%s: register %s\n", dev_name(dev->parent),
+		dev_name(dev));
+
+	return devm_add_action_or_reset(&cxlr->dev, cxlr_dax_unregister,
+					cxlr_dax);
+err:
+	put_device(dev);
+	return rc;
+}
+
+static int match_decoder_by_range(struct device *dev, void *data)
+{
+	struct range *r1, *r2 = data;
+	struct cxl_root_decoder *cxlrd;
+
+	if (!is_root_decoder(dev))
+		return 0;
+
+	cxlrd = to_cxl_root_decoder(dev);
+	r1 = &cxlrd->cxlsd.cxld.hpa_range;
+	return range_contains(r1, r2);
+}
+
+static int match_region_by_range(struct device *dev, void *data)
+{
+	struct cxl_region_params *p;
+	struct cxl_region *cxlr;
+	struct range *r = data;
+	int rc = 0;
+
+	if (!is_cxl_region(dev))
+		return 0;
+
+	cxlr = to_cxl_region(dev);
+	p = &cxlr->params;
+
+	down_read(&cxl_region_rwsem);
+	if (p->res && p->res->start == r->start && p->res->end == r->end)
+		rc = 1;
+	up_read(&cxl_region_rwsem);
+
+	return rc;
+}
+
+/* Establish an empty region covering the given HPA range */
+static struct cxl_region *construct_region(struct cxl_root_decoder *cxlrd,
+					   struct cxl_endpoint_decoder *cxled)
+{
+	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
+	struct cxl_port *port = cxlrd_to_port(cxlrd);
+	struct range *hpa = &cxled->cxld.hpa_range;
+	struct cxl_region_params *p;
+	struct cxl_region *cxlr;
+	struct resource *res;
+	int rc;
+
+	do {
+		cxlr = __create_region(cxlrd, cxled->mode,
+				       atomic_read(&cxlrd->region_id));
+	} while (IS_ERR(cxlr) && PTR_ERR(cxlr) == -EBUSY);
+
+	if (IS_ERR(cxlr)) {
+		dev_err(cxlmd->dev.parent,
+			"%s:%s: %s failed assign region: %ld\n",
+			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
+			__func__, PTR_ERR(cxlr));
+		return cxlr;
+	}
+
+	down_write(&cxl_region_rwsem);
+	p = &cxlr->params;
+	if (p->state >= CXL_CONFIG_INTERLEAVE_ACTIVE) {
+		dev_err(cxlmd->dev.parent,
+			"%s:%s: %s autodiscovery interrupted\n",
+			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
+			__func__);
+		rc = -EBUSY;
+		goto err;
+	}
+
+	set_bit(CXL_REGION_F_AUTO, &cxlr->flags);
+
+	res = kmalloc(sizeof(*res), GFP_KERNEL);
+	if (!res) {
+		rc = -ENOMEM;
+		goto err;
+	}
+
+	*res = DEFINE_RES_MEM_NAMED(hpa->start, range_len(hpa),
+				    dev_name(&cxlr->dev));
+	rc = insert_resource(cxlrd->res, res);
+	if (rc) {
+		/*
+		 * Platform-firmware may not have split resources like "System
+		 * RAM" on CXL window boundaries see cxl_region_iomem_release()
+		 */
+		dev_warn(cxlmd->dev.parent,
+			 "%s:%s: %s %s cannot insert resource\n",
+			 dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev),
+			 __func__, dev_name(&cxlr->dev));
+	}
+
+	p->res = res;
+	p->interleave_ways = cxled->cxld.interleave_ways;
+	p->interleave_granularity = cxled->cxld.interleave_granularity;
+	p->state = CXL_CONFIG_INTERLEAVE_ACTIVE;
+
+	rc = sysfs_update_group(&cxlr->dev.kobj, get_cxl_region_target_group());
+	if (rc)
+		goto err;
+
+	dev_dbg(cxlmd->dev.parent, "%s:%s: %s %s res: %pr iw: %d ig: %d\n",
+		dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev), __func__,
+		dev_name(&cxlr->dev), p->res, p->interleave_ways,
+		p->interleave_granularity);
+
+	/* ...to match put_device() in cxl_add_to_region() */
+	get_device(&cxlr->dev);
+	up_write(&cxl_region_rwsem);
+
+	return cxlr;
+
+err:
+	up_write(&cxl_region_rwsem);
+	devm_release_action(port->uport, unregister_region, cxlr);
+	return ERR_PTR(rc);
+}
+
+int cxl_add_to_region(struct cxl_port *root, struct cxl_endpoint_decoder *cxled)
+{
+	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
+	struct range *hpa = &cxled->cxld.hpa_range;
+	struct cxl_decoder *cxld = &cxled->cxld;
+	struct device *cxlrd_dev, *region_dev;
+	struct cxl_root_decoder *cxlrd;
+	struct cxl_region_params *p;
+	struct cxl_region *cxlr;
+	bool attach = false;
+	int rc;
+
+	cxlrd_dev = device_find_child(&root->dev, &cxld->hpa_range,
+				      match_decoder_by_range);
+	if (!cxlrd_dev) {
+		dev_err(cxlmd->dev.parent,
+			"%s:%s no CXL window for range %#llx:%#llx\n",
+			dev_name(&cxlmd->dev), dev_name(&cxld->dev),
+			cxld->hpa_range.start, cxld->hpa_range.end);
+		return -ENXIO;
+	}
+
+	cxlrd = to_cxl_root_decoder(cxlrd_dev);
+
+	/*
+	 * Ensure that if multiple threads race to construct_region() for @hpa
+	 * one does the construction and the others add to that.
+	 */
+	mutex_lock(&cxlrd->range_lock);
+	region_dev = device_find_child(&cxlrd->cxlsd.cxld.dev, hpa,
+				       match_region_by_range);
+	if (!region_dev) {
+		cxlr = construct_region(cxlrd, cxled);
+		region_dev = &cxlr->dev;
+	} else
+		cxlr = to_cxl_region(region_dev);
+	mutex_unlock(&cxlrd->range_lock);
+
+	if (IS_ERR(cxlr)) {
+		rc = PTR_ERR(cxlr);
+		goto out;
+	}
+
+	attach_target(cxlr, cxled, -1, TASK_UNINTERRUPTIBLE);
+
+	down_read(&cxl_region_rwsem);
+	p = &cxlr->params;
+	attach = p->state == CXL_CONFIG_COMMIT;
+	up_read(&cxl_region_rwsem);
+
+	if (attach) {
+		/*
+		 * If device_attach() fails the range may still be active via
+		 * the platform-firmware memory map, otherwise the driver for
+		 * regions is local to this file, so driver matching can't fail.
+		 */
+		if (device_attach(&cxlr->dev) < 0)
+			dev_err(&cxlr->dev, "failed to enable, range: %pr\n",
+				p->res);
+	}
+
+	put_device(region_dev);
+out:
+	put_device(cxlrd_dev);
+	return rc;
+}
+EXPORT_SYMBOL_NS_GPL(cxl_add_to_region, CXL);
+
 static int cxl_region_invalidate_memregion(struct cxl_region *cxlr)
 {
 	if (!test_bit(CXL_REGION_F_INCOHERENT, &cxlr->flags))
···
 	cpu_cache_invalidate_memregion(IORES_DESC_CXL);
 	clear_bit(CXL_REGION_F_INCOHERENT, &cxlr->flags);
 	return 0;
+}
+
+static int is_system_ram(struct resource *res, void *arg)
+{
+	struct cxl_region *cxlr = arg;
+	struct cxl_region_params *p = &cxlr->params;
+
+	dev_dbg(&cxlr->dev, "%pr has System RAM: %pr\n", p->res, res);
+	return 1;
 }
 
 static int cxl_region_probe(struct device *dev)
···
 	switch (cxlr->mode) {
 	case CXL_DECODER_PMEM:
 		return devm_cxl_add_pmem_region(cxlr);
+	case CXL_DECODER_RAM:
+		/*
+		 * The region can not be manged by CXL if any portion of
+		 * it is already online as 'System RAM'
+		 */
+		if (walk_iomem_res_desc(IORES_DESC_NONE,
+					IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY,
+					p->res->start, p->res->end, cxlr,
+					is_system_ram) > 0)
+			return 0;
+		return devm_cxl_add_dax_region(cxlr);
 	default:
 		dev_dbg(&cxlr->dev, "unsupported region mode: %d\n",
 			cxlr->mode);

drivers/cxl/cxl.h

···
  * cxl_decoder flags that define the type of memory / devices this
  * decoder supports as well as configuration lock status See "CXL 2.0
  * 8.2.5.12.7 CXL HDM Decoder 0 Control Register" for details.
+ * Additionally indicate whether decoder settings were autodetected,
+ * user customized.
  */
 #define CXL_DECODER_F_RAM   BIT(0)
 #define CXL_DECODER_F_PMEM  BIT(1)
···
 	CXL_DECODER_DEAD,
 };
 
+static inline const char *cxl_decoder_mode_name(enum cxl_decoder_mode mode)
+{
+	static const char * const names[] = {
+		[CXL_DECODER_NONE] = "none",
+		[CXL_DECODER_RAM] = "ram",
+		[CXL_DECODER_PMEM] = "pmem",
+		[CXL_DECODER_MIXED] = "mixed",
+	};
+
+	if (mode >= CXL_DECODER_NONE && mode <= CXL_DECODER_MIXED)
+		return names[mode];
+	return "mixed";
+}
+
+/*
+ * Track whether this decoder is reserved for region autodiscovery, or
+ * free for userspace provisioning.
+ */
+enum cxl_decoder_state {
+	CXL_DECODER_STATE_MANUAL,
+	CXL_DECODER_STATE_AUTO,
+};
+
 /**
  * struct cxl_endpoint_decoder - Endpoint  / SPA to DPA decoder
  * @cxld: base cxl_decoder_object
  * @dpa_res: actively claimed DPA span of this decoder
  * @skip: offset into @dpa_res where @cxld.hpa_range maps
  * @mode: which memory type / access-mode-partition this decoder targets
+ * @state: autodiscovery state
  * @pos: interleave position in @cxld.region
  */
 struct cxl_endpoint_decoder {
···
 	struct resource *dpa_res;
 	resource_size_t skip;
 	enum cxl_decoder_mode mode;
+	enum cxl_decoder_state state;
 	int pos;
 };
 
···
  * @region_id: region id for next region provisioning event
  * @calc_hb: which host bridge covers the n'th position by granularity
  * @platform_data: platform specific configuration data
+ * @range_lock: sync region autodiscovery by address range
  * @cxlsd: base cxl switch decoder
  */
 struct cxl_root_decoder {
···
 	atomic_t region_id;
 	cxl_calc_hb_fn calc_hb;
 	void *platform_data;
+	struct mutex range_lock;
 	struct cxl_switch_decoder cxlsd;
 };
 
···
  * CPU cache state at region activation time.
  */
 #define CXL_REGION_F_INCOHERENT 0
+
+/*
+ * Indicate whether this region has been assembled by autodetection or
+ * userspace assembly. Prevent endpoint decoders outside of automatic
+ * detection from being added to the region.
+ */
+#define CXL_REGION_F_AUTO 1
 
 /**
  * struct cxl_region - CXL region
···
 	struct range hpa_range;
 	int nr_mappings;
 	struct cxl_pmem_region_mapping mapping[];
+};
+
+struct cxl_dax_region {
+	struct device dev;
+	struct cxl_region *cxlr;
+	struct range hpa_range;
 };
 
 /**
···
 
 struct cxl_decoder *to_cxl_decoder(struct device *dev);
 struct cxl_root_decoder *to_cxl_root_decoder(struct device *dev);
+struct cxl_switch_decoder *to_cxl_switch_decoder(struct device *dev);
 struct cxl_endpoint_decoder *to_cxl_endpoint_decoder(struct device *dev);
 bool is_root_decoder(struct device *dev);
+bool is_switch_decoder(struct device *dev);
 bool is_endpoint_decoder(struct device *dev);
 struct cxl_root_decoder *cxl_root_decoder_alloc(struct cxl_port *port,
 						unsigned int nr_targets,
···
 #define CXL_DEVICE_MEMORY_EXPANDER	5
 #define CXL_DEVICE_REGION		6
 #define CXL_DEVICE_PMEM_REGION		7
+#define CXL_DEVICE_DAX_REGION		8
 
 #define MODULE_ALIAS_CXL(type) MODULE_ALIAS("cxl:t" __stringify(type) "*")
 #define CXL_MODALIAS_FMT "cxl:t%d"
···
 #ifdef CONFIG_CXL_REGION
 bool is_cxl_pmem_region(struct device *dev);
 struct cxl_pmem_region *to_cxl_pmem_region(struct device *dev);
+int cxl_add_to_region(struct cxl_port *root,
+		      struct cxl_endpoint_decoder *cxled);
+struct cxl_dax_region *to_cxl_dax_region(struct device *dev);
 #else
 static inline bool is_cxl_pmem_region(struct device *dev)
 {
 	return false;
 }
 static inline struct cxl_pmem_region *to_cxl_pmem_region(struct device *dev)
+{
+	return NULL;
+}
+static inline int cxl_add_to_region(struct cxl_port *root,
+				    struct cxl_endpoint_decoder *cxled)
+{
+	return 0;
+}
+static inline struct cxl_dax_region *to_cxl_dax_region(struct device *dev)
 {
 	return NULL;
 }

drivers/cxl/cxlmem.h

···
  * @cxl_nvb: coordinate removal of @cxl_nvd if present
  * @cxl_nvd: optional bridge to an nvdimm if the device supports pmem
  * @id: id number of this memdev instance.
+ * @depth: endpoint port depth
  */
 struct cxl_memdev {
 	struct device dev;
···
 	struct cxl_nvdimm_bridge *cxl_nvb;
 	struct cxl_nvdimm *cxl_nvd;
 	int id;
+	int depth;
 };
 
 static inline struct cxl_memdev *to_cxl_memdev(struct device *dev)
···
 }
 
 struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds);
+int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
+			 resource_size_t base, resource_size_t len,
+			 resource_size_t skipped);
 
 static inline struct cxl_ep *cxl_ep_load(struct cxl_port *port,
 					 struct cxl_memdev *cxlmd)

drivers/cxl/port.c

···
 	schedule_cxl_memdev_detach(cxlmd);
 }
 
-static int cxl_port_probe(struct device *dev)
+static int discover_region(struct device *dev, void *root)
 {
-	struct cxl_port *port = to_cxl_port(dev);
+	struct cxl_endpoint_decoder *cxled;
+	int rc;
+
+	if (!is_endpoint_decoder(dev))
+		return 0;
+
+	cxled = to_cxl_endpoint_decoder(dev);
+	if ((cxled->cxld.flags & CXL_DECODER_F_ENABLE) == 0)
+		return 0;
+
+	if (cxled->state != CXL_DECODER_STATE_AUTO)
+		return 0;
+
+	/*
+	 * Region enumeration is opportunistic, if this add-event fails,
+	 * continue to the next endpoint decoder.
+	 */
+	rc = cxl_add_to_region(root, cxled);
+	if (rc)
+		dev_dbg(dev, "failed to add to region: %#llx-%#llx\n",
+			cxled->cxld.hpa_range.start, cxled->cxld.hpa_range.end);
+
+	return 0;
+}
+
+static int cxl_switch_port_probe(struct cxl_port *port)
+{
 	struct cxl_hdm *cxlhdm;
 	int rc;
 
+	rc = devm_cxl_port_enumerate_dports(port);
+	if (rc < 0)
+		return rc;
 
-	if (!is_cxl_endpoint(port)) {
-		rc = devm_cxl_port_enumerate_dports(port);
-		if (rc < 0)
-			return rc;
-		if (rc == 1)
-			return devm_cxl_add_passthrough_decoder(port);
-	}
+	if (rc == 1)
+		return devm_cxl_add_passthrough_decoder(port);
 
 	cxlhdm = devm_cxl_setup_hdm(port);
 	if (IS_ERR(cxlhdm))
 		return PTR_ERR(cxlhdm);
 
-	if (is_cxl_endpoint(port)) {
-		struct cxl_memdev *cxlmd = to_cxl_memdev(port->uport);
-		struct cxl_dev_state *cxlds = cxlmd->cxlds;
+	return devm_cxl_enumerate_decoders(cxlhdm);
+}
 
-		/* Cache the data early to ensure is_visible() works */
-		read_cdat_data(port);
+static int cxl_endpoint_port_probe(struct cxl_port *port)
+{
+	struct cxl_memdev *cxlmd = to_cxl_memdev(port->uport);
+	struct cxl_dev_state *cxlds = cxlmd->cxlds;
+	struct cxl_hdm *cxlhdm;
+	struct cxl_port *root;
+	int rc;
 
-		get_device(&cxlmd->dev);
-		rc = devm_add_action_or_reset(dev, schedule_detach, cxlmd);
-		if (rc)
-			return rc;
+	cxlhdm = devm_cxl_setup_hdm(port);
+	if (IS_ERR(cxlhdm))
+		return PTR_ERR(cxlhdm);
 
-		rc = cxl_hdm_decode_init(cxlds, cxlhdm);
-		if (rc)
-			return rc;
+	/* Cache the data early to ensure is_visible() works */
+	read_cdat_data(port);
 
-		rc = cxl_await_media_ready(cxlds);
-		if (rc) {
-			dev_err(dev, "Media not active (%d)\n", rc);
-			return rc;
-		}
-	}
+	get_device(&cxlmd->dev);
+	rc = devm_add_action_or_reset(&port->dev, schedule_detach, cxlmd);
+	if (rc)
+		return rc;
 
-	rc = devm_cxl_enumerate_decoders(cxlhdm);
+	rc = cxl_hdm_decode_init(cxlds, cxlhdm);
+	if (rc)
+		return rc;
+
+	rc = cxl_await_media_ready(cxlds);
 	if (rc) {
-		dev_err(dev, "Couldn't enumerate decoders (%d)\n", rc);
+		dev_err(&port->dev, "Media not active (%d)\n", rc);
 		return rc;
 	}
 
+	rc = devm_cxl_enumerate_decoders(cxlhdm);
+	if (rc)
+		return rc;
+
+	/*
+	 * This can't fail in practice as CXL root exit unregisters all
+	 * descendant ports and that in turn synchronizes with cxl_port_probe()
+	 */
+	root = find_cxl_root(&cxlmd->dev);
+
+	/*
+	 * Now that all endpoint decoders are successfully enumerated, try to
+	 * assemble regions from committed decoders
+	 */
+	device_for_each_child(&port->dev, root, discover_region);
+	put_device(&root->dev);
+
 	return 0;
+}
+
+static int cxl_port_probe(struct device *dev)
+{
+	struct cxl_port *port = to_cxl_port(dev);
+
+	if (is_cxl_endpoint(port))
+		return cxl_endpoint_port_probe(port);
+	return cxl_switch_port_probe(port);
 }
 
 static ssize_t CDAT_read(struct file *filp, struct kobject *kobj,

drivers/dax/Kconfig

···
 
 	  Say M if unsure.
 
+config DEV_DAX_CXL
+	tristate "CXL DAX: direct access to CXL RAM regions"
+	depends on CXL_REGION && DEV_DAX
+	default CXL_REGION && DEV_DAX
+	help
+	  CXL RAM regions are either mapped by platform-firmware
+	  and published in the initial system-memory map as "System RAM", mapped
+	  by platform-firmware as "Soft Reserved", or dynamically provisioned
+	  after boot by the CXL driver. In the latter two cases a device-dax
+	  instance is created to access that unmapped-by-default address range.
+	  Per usual it can remain as dedicated access via a device interface, or
+	  converted to "System RAM" via the dax_kmem facility.
+
 config DEV_DAX_HMEM_DEVICES
-	depends on DEV_DAX_HMEM && DAX=y
+	depends on DEV_DAX_HMEM && DAX
 	def_bool y
 
 config DEV_DAX_KMEM
-	tristate "KMEM DAX: volatile-use of persistent memory"
+	tristate "KMEM DAX: map dax-devices as System-RAM"
 	default DEV_DAX
 	depends on DEV_DAX
 	depends on MEMORY_HOTPLUG # for add_memory() and friends

drivers/dax/Makefile

···
 obj-$(CONFIG_DEV_DAX) += device_dax.o
 obj-$(CONFIG_DEV_DAX_KMEM) += kmem.o
 obj-$(CONFIG_DEV_DAX_PMEM) += dax_pmem.o
+obj-$(CONFIG_DEV_DAX_CXL) += dax_cxl.o
 
 dax-y := super.o
 dax-y += bus.o
 device_dax-y := device.o
 dax_pmem-y := pmem.o
+dax_cxl-y := cxl.o
 
 obj-y += hmem/

drivers/dax/bus.c

···
 	return match;
 }
 
+static int dax_match_type(struct dax_device_driver *dax_drv, struct device *dev)
+{
+	enum dax_driver_type type = DAXDRV_DEVICE_TYPE;
+	struct dev_dax *dev_dax = to_dev_dax(dev);
+
+	if (dev_dax->region->res.flags & IORESOURCE_DAX_KMEM)
+		type = DAXDRV_KMEM_TYPE;
+
+	if (dax_drv->type == type)
+		return 1;
+
+	/* default to device mode if dax_kmem is disabled */
+	if (dax_drv->type == DAXDRV_DEVICE_TYPE &&
+	    !IS_ENABLED(CONFIG_DEV_DAX_KMEM))
+		return 1;
+
+	return 0;
+}
+
 enum id_action {
 	ID_REMOVE,
 	ID_ADD,
···
 {
 	struct dax_device_driver *dax_drv = to_dax_drv(drv);
 
-	/*
-	 * All but the 'device-dax' driver, which has 'match_always'
-	 * set, requires an exact id match.
-	 */
-	if (dax_drv->match_always)
+	if (dax_match_id(dax_drv, dev))
 		return 1;
-
-	return dax_match_id(dax_drv, dev);
+	return dax_match_type(dax_drv, dev);
 }
 
 /*
···
 }
 EXPORT_SYMBOL_GPL(devm_create_dev_dax);
 
-static int match_always_count;
-
 int __dax_driver_register(struct dax_device_driver *dax_drv,
 		struct module *module, const char *mod_name)
 {
 	struct device_driver *drv = &dax_drv->drv;
-	int rc = 0;
 
 	/*
 	 * dax_bus_probe() calls dax_drv->probe() unconditionally.
···
 	drv->mod_name = mod_name;
 	drv->bus = &dax_bus_type;
 
-	/* there can only be one default driver */
-	mutex_lock(&dax_bus_lock);
-	match_always_count += dax_drv->match_always;
-	if (match_always_count > 1) {
-		match_always_count--;
-		WARN_ON(1);
-		rc = -EINVAL;
-	}
-	mutex_unlock(&dax_bus_lock);
-	if (rc)
-		return rc;
-
-	rc = driver_register(drv);
-	if (rc && dax_drv->match_always) {
-		mutex_lock(&dax_bus_lock);
-		match_always_count -= dax_drv->match_always;
-		mutex_unlock(&dax_bus_lock);
-	}
-
-	return rc;
+	return driver_register(drv);
 }
 EXPORT_SYMBOL_GPL(__dax_driver_register);
 
···
 	struct dax_id *dax_id, *_id;
 
 	mutex_lock(&dax_bus_lock);
-	match_always_count -= dax_drv->match_always;
 	list_for_each_entry_safe(dax_id, _id, &dax_drv->ids, list) {
 		list_del(&dax_id->list);
 		kfree(dax_id);

drivers/dax/bus.h

···
 struct dax_region;
 void dax_region_put(struct dax_region *dax_region);
 
-#define IORESOURCE_DAX_STATIC (1UL << 0)
+/* dax bus specific ioresource flags */
+#define IORESOURCE_DAX_STATIC BIT(0)
+#define IORESOURCE_DAX_KMEM BIT(1)
+
 struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 		struct range *range, int target_node, unsigned int align,
 		unsigned long flags);
···
 
 struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data);
 
+enum dax_driver_type {
+	DAXDRV_KMEM_TYPE,
+	DAXDRV_DEVICE_TYPE,
+};
+
 struct dax_device_driver {
 	struct device_driver drv;
 	struct list_head ids;
-	int match_always;
+	enum dax_driver_type type;
 	int (*probe)(struct dev_dax *dev);
 	void (*remove)(struct dev_dax *dev);
 };

drivers/dax/cxl.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright(c) 2023 Intel Corporation. All rights reserved. */
+#include <linux/module.h>
+#include <linux/dax.h>
+
+#include "../cxl/cxl.h"
+#include "bus.h"
+
+static int cxl_dax_region_probe(struct device *dev)
+{
+	struct cxl_dax_region *cxlr_dax = to_cxl_dax_region(dev);
+	int nid = phys_to_target_node(cxlr_dax->hpa_range.start);
+	struct cxl_region *cxlr = cxlr_dax->cxlr;
+	struct dax_region *dax_region;
+	struct dev_dax_data data;
+	struct dev_dax *dev_dax;
+
+	if (nid == NUMA_NO_NODE)
+		nid = memory_add_physaddr_to_nid(cxlr_dax->hpa_range.start);
+
+	dax_region = alloc_dax_region(dev, cxlr->id, &cxlr_dax->hpa_range, nid,
+				      PMD_SIZE, IORESOURCE_DAX_KMEM);
+	if (!dax_region)
+		return -ENOMEM;
+
+	data = (struct dev_dax_data) {
+		.dax_region = dax_region,
+		.id = -1,
+		.size = range_len(&cxlr_dax->hpa_range),
+	};
+	dev_dax = devm_create_dev_dax(&data);
+	if (IS_ERR(dev_dax))
+		return PTR_ERR(dev_dax);
+
+	/* child dev_dax instances now own the lifetime of the dax_region */
+	dax_region_put(dax_region);
+	return 0;
+}
+
+static struct cxl_driver cxl_dax_region_driver = {
+	.name = "cxl_dax_region",
+	.probe = cxl_dax_region_probe,
+	.id = CXL_DEVICE_DAX_REGION,
+	.drv = {
+		.suppress_bind_attrs = true,
+	},
+};
+
+module_cxl_driver(cxl_dax_region_driver);
+MODULE_ALIAS_CXL(CXL_DEVICE_DAX_REGION);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Intel Corporation");
+MODULE_IMPORT_NS(CXL);

drivers/dax/device.c

···
 
 static struct dax_device_driver device_dax_driver = {
 	.probe = dev_dax_probe,
-	/* all probe actions are unwound by devm, so .remove isn't necessary */
-	.match_always = 1,
+	.type = DAXDRV_DEVICE_TYPE,
 };
 
 static int __init dax_init(void)

drivers/dax/hmem/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-obj-$(CONFIG_DEV_DAX_HMEM) += dax_hmem.o
+# device_hmem.o deliberately precedes dax_hmem.o for initcall ordering
 obj-$(CONFIG_DEV_DAX_HMEM_DEVICES) += device_hmem.o
+obj-$(CONFIG_DEV_DAX_HMEM) += dax_hmem.o
 
 device_hmem-y := device.o
 dax_hmem-y := hmem.o

drivers/dax/hmem/device.c

···
 static bool nohmem;
 module_param_named(disable, nohmem, bool, 0444);
 
+static bool platform_initialized;
+static DEFINE_MUTEX(hmem_resource_lock);
 static struct resource hmem_active = {
 	.name = "HMEM devices",
 	.start = 0,
···
 	.flags = IORESOURCE_MEM,
 };
 
-void hmem_register_device(int target_nid, struct resource *r)
+int walk_hmem_resources(struct device *host, walk_hmem_fn fn)
 {
-	/* define a clean / non-busy resource for the platform device */
-	struct resource res = {
-		.start = r->start,
-		.end = r->end,
-		.flags = IORESOURCE_MEM,
-		.desc = IORES_DESC_SOFT_RESERVED,
-	};
+	struct resource *res;
+	int rc = 0;
+
+	mutex_lock(&hmem_resource_lock);
+	for (res = hmem_active.child; res; res = res->sibling) {
+		rc = fn(host, (int) res->desc, res);
+		if (rc)
+			break;
+	}
+	mutex_unlock(&hmem_resource_lock);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(walk_hmem_resources);
+
+static void __hmem_register_resource(int target_nid, struct resource *res)
+{
 	struct platform_device *pdev;
-	struct memregion_info info;
-	int rc, id;
+	struct resource *new;
+	int rc;
 
-	if (nohmem)
-		return;
-
-	rc = region_intersects(res.start, resource_size(&res), IORESOURCE_MEM,
-			IORES_DESC_SOFT_RESERVED);
-	if (rc != REGION_INTERSECTS)
-		return;
-
-	id = memregion_alloc(GFP_KERNEL);
-	if (id < 0) {
-		pr_err("memregion allocation failure for %pr\n", &res);
+	new = __request_region(&hmem_active, res->start, resource_size(res), "",
+			       0);
+	if (!new) {
+		pr_debug("hmem range %pr already active\n", res);
 		return;
 	}
 
-	pdev = platform_device_alloc("hmem", id);
+	new->desc = target_nid;
+
+	if (platform_initialized)
+		return;
+
+	pdev = platform_device_alloc("hmem_platform", 0);
 	if (!pdev) {
-		pr_err("hmem device allocation failure for %pr\n", &res);
-		goto out_pdev;
-	}
-
-	if (!__request_region(&hmem_active, res.start, resource_size(&res),
-			      dev_name(&pdev->dev), 0)) {
-		dev_dbg(&pdev->dev, "hmem range %pr already active\n", &res);
-		goto out_active;
-	}
-
-	pdev->dev.numa_node = numa_map_to_online_node(target_nid);
-	info = (struct memregion_info) {
-		.target_node = target_nid,
-	};
-	rc = platform_device_add_data(pdev, &info, sizeof(info));
-	if (rc < 0) {
-		pr_err("hmem memregion_info allocation failure for %pr\n", &res);
-		goto out_resource;
-	}
-
-	rc = platform_device_add_resources(pdev, &res, 1);
-	if (rc < 0) {
-		pr_err("hmem resource allocation failure for %pr\n", &res);
-		goto out_resource;
+		pr_err_once("failed to register device-dax hmem_platform device\n");
+		return;
 	}
 
 	rc = platform_device_add(pdev);
-	if (rc < 0) {
-		dev_err(&pdev->dev, "device add failed for %pr\n", &res);
-		goto out_resource;
-	}
+	if (rc)
+		platform_device_put(pdev);
+	else
+		platform_initialized = true;
+}
 
-	return;
+void hmem_register_resource(int target_nid, struct resource *res)
+{
+	if (nohmem)
+		return;
 
-out_resource:
-	__release_region(&hmem_active, res.start, resource_size(&res));
-out_active:
-	platform_device_put(pdev);
-out_pdev:
-	memregion_free(id);
+	mutex_lock(&hmem_resource_lock);
+	__hmem_register_resource(target_nid, res);
+	mutex_unlock(&hmem_resource_lock);
 }
 
 static __init int hmem_register_one(struct resource *res, void *data)
 {
-	hmem_register_device(phys_to_target_node(res->start), res);
+	hmem_register_resource(phys_to_target_node(res->start), res);
 
 	return 0;
 }
···
  * As this is a fallback for address ranges unclaimed by the ACPI HMAT
  * parsing it must be at an initcall level greater than hmat_init().
  */
-late_initcall(hmem_init);
+device_initcall(hmem_init);

drivers/dax/hmem/hmem.c

···
 #include <linux/memregion.h>
 #include <linux/module.h>
 #include <linux/pfn_t.h>
+#include <linux/dax.h>
 #include "../bus.h"
 
 static bool region_idle;
···
 
 static int dax_hmem_probe(struct platform_device *pdev)
 {
+	unsigned long flags = IORESOURCE_DAX_KMEM;
 	struct device *dev = &pdev->dev;
 	struct dax_region *dax_region;
 	struct memregion_info *mri;
 	struct dev_dax_data data;
 	struct dev_dax *dev_dax;
-	struct resource *res;
-	struct range range;
 
-	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-	if (!res)
-		return -ENOMEM;
+	/*
+	 * @region_idle == true indicates that an administrative agent
+	 * wants to manipulate the range partitioning before the devices
+	 * are created, so do not send them to the dax_kmem driver by
+	 * default.
+	 */
+	if (region_idle)
+		flags = 0;
 
 	mri = dev->platform_data;
-	range.start = res->start;
-	range.end = res->end;
-	dax_region = alloc_dax_region(dev, pdev->id, &range, mri->target_node,
-			PMD_SIZE, 0);
+	dax_region = alloc_dax_region(dev, pdev->id, &mri->range,
+				      mri->target_node, PMD_SIZE, flags);
 	if (!dax_region)
 		return -ENOMEM;
 
 	data = (struct dev_dax_data) {
 		.dax_region = dax_region,
 		.id = -1,
-		.size = region_idle ? 0 : resource_size(res),
+		.size = region_idle ? 0 : range_len(&mri->range),
 	};
 	dev_dax = devm_create_dev_dax(&data);
 	if (IS_ERR(dev_dax))
···
 	return 0;
 }
 
-static int dax_hmem_remove(struct platform_device *pdev)
-{
-	/* devm handles teardown */
-	return 0;
-}
-
 static struct platform_driver dax_hmem_driver = {
 	.probe = dax_hmem_probe,
-	.remove = dax_hmem_remove,
 	.driver = {
 		.name = "hmem",
 	},
 };
 
-module_platform_driver(dax_hmem_driver);
+static void release_memregion(void *data)
+{
+	memregion_free((long) data);
+}
+
+static void release_hmem(void *pdev)
+{
+	platform_device_unregister(pdev);
+}
+
+static int hmem_register_device(struct device *host, int target_nid,
+				const struct resource *res)
+{
+	struct platform_device *pdev;
+	struct memregion_info info;
+	long id;
+	int rc;
+
+	if (IS_ENABLED(CONFIG_CXL_REGION) &&
+	    region_intersects(res->start, resource_size(res), IORESOURCE_MEM,
+			      IORES_DESC_CXL) != REGION_DISJOINT) {
+		dev_dbg(host, "deferring range to CXL: %pr\n", res);
+		return 0;
+	}
+
+	rc = region_intersects(res->start, resource_size(res), IORESOURCE_MEM,
+			       IORES_DESC_SOFT_RESERVED);
+	if (rc != REGION_INTERSECTS)
+		return 0;
+
+	id = memregion_alloc(GFP_KERNEL);
+	if (id < 0) {
+		dev_err(host, "memregion allocation failure for %pr\n", res);
+		return -ENOMEM;
+	}
+	rc = devm_add_action_or_reset(host, release_memregion, (void *) id);
+	if (rc)
+		return rc;
+
+	pdev = platform_device_alloc("hmem", id);
+	if (!pdev) {
+		dev_err(host, "device allocation failure for %pr\n", res);
+		return -ENOMEM;
+	}
+
+	pdev->dev.numa_node = numa_map_to_online_node(target_nid);
+	info = (struct memregion_info) {
+		.target_node = target_nid,
+		.range = {
+			.start = res->start,
+			.end = res->end,
+		},
+	};
+	rc = platform_device_add_data(pdev, &info, sizeof(info));
+	if (rc < 0) {
+		dev_err(host, "memregion_info allocation failure for %pr\n",
+		       res);
+		goto out_put;
+	}
+
+	rc = platform_device_add(pdev);
+	if (rc < 0) {
+		dev_err(host, "%s add failed for %pr\n", dev_name(&pdev->dev),
+			res);
+		goto out_put;
+	}
+
+	return devm_add_action_or_reset(host, release_hmem, pdev);
+
+out_put:
+	platform_device_put(pdev);
+	return rc;
+}
+
+static int dax_hmem_platform_probe(struct platform_device *pdev)
+{
+	return walk_hmem_resources(&pdev->dev, hmem_register_device);
+}
+
+static struct platform_driver dax_hmem_platform_driver = {
+	.probe = dax_hmem_platform_probe,
+	.driver = {
+		.name = "hmem_platform",
+	},
+};
+
+static __init int dax_hmem_init(void)
+{
+	int rc;
+
+	rc = platform_driver_register(&dax_hmem_platform_driver);
+	if (rc)
+		return rc;
+
+	rc = platform_driver_register(&dax_hmem_driver);
+	if (rc)
+		platform_driver_unregister(&dax_hmem_platform_driver);
+
+	return rc;
+}
+
+static __exit void dax_hmem_exit(void)
+{
+	platform_driver_unregister(&dax_hmem_driver);
+	platform_driver_unregister(&dax_hmem_platform_driver);
+}
+
+module_init(dax_hmem_init);
+module_exit(dax_hmem_exit);
+
+/* Allow for CXL to define its own dax regions */
+#if IS_ENABLED(CONFIG_CXL_REGION)
+#if IS_MODULE(CONFIG_CXL_ACPI)
+MODULE_SOFTDEP("pre: cxl_acpi");
+#endif
+#endif
 
 MODULE_ALIAS("platform:hmem*");
+MODULE_ALIAS("platform:hmem_platform*");
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Intel Corporation");

drivers/dax/kmem.c

···
 static struct dax_device_driver device_dax_kmem_driver = {
 	.probe = dev_dax_kmem_probe,
 	.remove = dev_dax_kmem_remove,
+	.type = DAXDRV_KMEM_TYPE,
 };
 
 static int __init dax_kmem_init(void)

include/linux/dax.h

···
 }
 
 #ifdef CONFIG_DEV_DAX_HMEM_DEVICES
-void hmem_register_device(int target_nid, struct resource *r);
+void hmem_register_resource(int target_nid, struct resource *r);
 #else
-static inline void hmem_register_device(int target_nid, struct resource *r)
+static inline void hmem_register_resource(int target_nid, struct resource *r)
 {
 }
 #endif
 
+typedef int (*walk_hmem_fn)(struct device *dev, int target_nid,
+			    const struct resource *res);
+int walk_hmem_resources(struct device *dev, walk_hmem_fn fn);
 #endif

include/linux/memregion.h

···
 #define _MEMREGION_H_
 #include <linux/types.h>
 #include <linux/errno.h>
+#include <linux/range.h>
 #include <linux/bug.h>
 
 struct memregion_info {
 	int target_node;
+	struct range range;
 };
 
 #ifdef CONFIG_MEMREGION

include/linux/range.h

···
 	return range->end - range->start + 1;
 }
 
+static inline bool range_contains(struct range *r1, struct range *r2)
+{
+	return r1->start <= r2->start && r1->end >= r2->end;
+}
+
 int add_range(struct range *range, int az, int nr_range,
 		u64 start, u64 end);
 

lib/stackinit_kunit.c

···
 static void *fill_start, *target_start;
 static size_t fill_size, target_size;
 
-static bool range_contains(char *haystack_start, size_t haystack_size,
-			   char *needle_start, size_t needle_size)
+static bool stackinit_range_contains(char *haystack_start, size_t haystack_size,
+				     char *needle_start, size_t needle_size)
 {
 	if (needle_start >= haystack_start &&
 	    needle_start + needle_size <= haystack_start + haystack_size)
···
 								\
 	/* Validate that compiler lined up fill and target. */	\
 	KUNIT_ASSERT_TRUE_MSG(test,				\
-		range_contains(fill_start, fill_size,		\
+		stackinit_range_contains(fill_start, fill_size,	\
 			    target_start, target_size),		\
 		"stack fill missed target!? "			\
 		"(fill %zu wide, target offset by %d)\n",	\

tools/testing/cxl/test/cxl.c

···
 	return 0;
 }
 
+static void default_mock_decoder(struct cxl_decoder *cxld)
+{
+	cxld->hpa_range = (struct range){
+		.start = 0,
+		.end = -1,
+	};
+
+	cxld->interleave_ways = 1;
+	cxld->interleave_granularity = 256;
+	cxld->target_type = CXL_DECODER_EXPANDER;
+	cxld->commit = mock_decoder_commit;
+	cxld->reset = mock_decoder_reset;
+}
+
+static int first_decoder(struct device *dev, void *data)
+{
+	struct cxl_decoder *cxld;
+
+	if (!is_switch_decoder(dev))
+		return 0;
+	cxld = to_cxl_decoder(dev);
+	if (cxld->id == 0)
+		return 1;
+	return 0;
+}
+
+static void mock_init_hdm_decoder(struct cxl_decoder *cxld)
+{
+	struct acpi_cedt_cfmws *window = mock_cfmws[0];
+	struct platform_device *pdev = NULL;
+	struct cxl_endpoint_decoder *cxled;
+	struct cxl_switch_decoder *cxlsd;
+	struct cxl_port *port, *iter;
+	const int size = SZ_512M;
+	struct cxl_memdev *cxlmd;
+	struct cxl_dport *dport;
+	struct device *dev;
+	bool hb0 = false;
+	u64 base;
+	int i;
+
+	if (is_endpoint_decoder(&cxld->dev)) {
+		cxled = to_cxl_endpoint_decoder(&cxld->dev);
+		cxlmd = cxled_to_memdev(cxled);
+		WARN_ON(!dev_is_platform(cxlmd->dev.parent));
+		pdev = to_platform_device(cxlmd->dev.parent);
+
+		/* check is endpoint is attach to host-bridge0 */
+		port = cxled_to_port(cxled);
+		do {
+			if (port->uport == &cxl_host_bridge[0]->dev) {
+				hb0 = true;
+				break;
+			}
+			if (is_cxl_port(port->dev.parent))
+				port = to_cxl_port(port->dev.parent);
+			else
+				port = NULL;
+		} while (port);
+		port = cxled_to_port(cxled);
+	}
+
+	/*
+	 * The first decoder on the first 2 devices on the first switch
+	 * attached to host-bridge0 mock a fake / static RAM region. All
+	 * other decoders are default disabled. Given the round robin
+	 * assignment those devices are named cxl_mem.0, and cxl_mem.4.
+	 *
+	 * See 'cxl list -BMPu -m cxl_mem.0,cxl_mem.4'
+	 */
+	if (!hb0 || pdev->id % 4 || pdev->id > 4 || cxld->id > 0) {
+		default_mock_decoder(cxld);
+		return;
+	}
+
+	base = window->base_hpa;
+	cxld->hpa_range = (struct range) {
+		.start = base,
+		.end = base + size - 1,
+	};
+
+	cxld->interleave_ways = 2;
+	eig_to_granularity(window->granularity, &cxld->interleave_granularity);
+	cxld->target_type = CXL_DECODER_EXPANDER;
+	cxld->flags = CXL_DECODER_F_ENABLE;
+	cxled->state = CXL_DECODER_STATE_AUTO;
+	port->commit_end = cxld->id;
+	devm_cxl_dpa_reserve(cxled, 0, size / cxld->interleave_ways, 0);
+	cxld->commit = mock_decoder_commit;
+	cxld->reset = mock_decoder_reset;
+
+	/*
+	 * Now that endpoint decoder is set up, walk up the hierarchy
+	 * and setup the switch and root port decoders targeting @cxlmd.
+	 */
+	iter = port;
+	for (i = 0; i < 2; i++) {
+		dport = iter->parent_dport;
+		iter = dport->port;
+		dev = device_find_child(&iter->dev, NULL, first_decoder);
+		/*
+		 * Ancestor ports are guaranteed to be enumerated before
+		 * @port, and all ports have at least one decoder.
+		 */
+		if (WARN_ON(!dev))
+			continue;
+		cxlsd = to_cxl_switch_decoder(dev);
+		if (i == 0) {
+			/* put cxl_mem.4 second in the decode order */
+			if (pdev->id == 4)
+				cxlsd->target[1] = dport;
+			else
+				cxlsd->target[0] = dport;
+		} else
+			cxlsd->target[0] = dport;
+		cxld = &cxlsd->cxld;
+		cxld->target_type = CXL_DECODER_EXPANDER;
+		cxld->flags = CXL_DECODER_F_ENABLE;
+		iter->commit_end = 0;
+		/*
+		 * Switch targets 2 endpoints, while host bridge targets
+		 * one root port
+		 */
+		if (i == 0)
+			cxld->interleave_ways = 2;
+		else
+			cxld->interleave_ways = 1;
+		cxld->interleave_granularity = 256;
+		cxld->hpa_range = (struct range) {
+			.start = base,
+			.end = base + size - 1,
+		};
+		put_device(dev);
+	}
+}
+
 static int mock_cxl_enumerate_decoders(struct cxl_hdm *cxlhdm)
 {
 	struct cxl_port *port = cxlhdm->port;
···
 			cxld = &cxled->cxld;
 		}
 
-		cxld->hpa_range = (struct range) {
-			.start = 0,
-			.end = -1,
-		};
-
-		cxld->interleave_ways = min_not_zero(target_count, 1);
-		cxld->interleave_granularity = SZ_4K;
-		cxld->target_type = CXL_DECODER_EXPANDER;
-		cxld->commit = mock_decoder_commit;
-		cxld->reset = mock_decoder_reset;
+		mock_init_hdm_decoder(cxld);
 
 		if (target_count) {
 			rc = device_for_each_child(port->uport, &ctx,