[PATCH 2/5] cxl/region: Add dynamic capacity cxl region support.

[ira.weiny@intel.com]

From: Navneet Singh <navneet.singh@intel.com>

CXL devices optionally support dynamic capacity. CXL Regions must be
created to access this capacity.

Add sysfs entries to create dynamic capacity cxl regions. Provide a new
Dynamic Capacity decoder mode which targets dynamic capacity on devices
which are added to that region.

Below are the steps to create and delete dynamic capacity region0
(example).

    region=$(cat /sys/bus/cxl/devices/decoder0.0/create_dc_region)
    echo $region> /sys/bus/cxl/devices/decoder0.0/create_dc_region
    echo 256 > /sys/bus/cxl/devices/$region/interleave_granularity
    echo 1 > /sys/bus/cxl/devices/$region/interleave_ways

    echo "dc0" >/sys/bus/cxl/devices/decoder1.0/mode
    echo 0x400000000 >/sys/bus/cxl/devices/decoder1.0/dpa_size

    echo 0x400000000 > /sys/bus/cxl/devices/$region/size
    echo  "decoder1.0" > /sys/bus/cxl/devices/$region/target0
    echo 1 > /sys/bus/cxl/devices/$region/commit
    echo $region > /sys/bus/cxl/drivers/cxl_region/bind

    echo $region> /sys/bus/cxl/devices/decoder0.0/delete_region

Signed-off-by: Navneet Singh <navneet.singh@intel.com>

---
[iweiny: fixups]
[iweiny: remove unused CXL_DC_REGION_MODE macro]
[iweiny: Make dc_mode_to_region_index static]
[iweiny: simplify <sysfs>/create_dc_region]
[iweiny: introduce decoder_mode_is_dc]
[djbw: fixups, no sign-off: preview only]
---
 drivers/cxl/Kconfig       |  11 +++
 drivers/cxl/core/core.h   |   7 ++
 drivers/cxl/core/hdm.c    | 234 ++++++++++++++++++++++++++++++++++++++++++----
 drivers/cxl/core/port.c   |  18 ++++
 drivers/cxl/core/region.c | 135 ++++++++++++++++++++++++--
 drivers/cxl/cxl.h         |  28 ++++++
 drivers/dax/cxl.c         |   4 +
 7 files changed, 409 insertions(+), 28 deletions(-)

diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index ff4e78117b31..df034889d053 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -121,6 +121,17 @@ config CXL_REGION
 
 	  If unsure say 'y'
 
+config CXL_DCD
+	bool "CXL: DCD Support"
+	default CXL_BUS
+	depends on CXL_REGION
+	help
+	  Enable the CXL core to provision CXL DCD regions.
+	  CXL devices optionally support dynamic capacity and DCD region
+	  maps the dynamic capacity regions DPA's into Host HPA ranges.
+
+	  If unsure say 'y'
+
 config CXL_REGION_INVALIDATION_TEST
 	bool "CXL: Region Cache Management Bypass (TEST)"
 	depends on CXL_REGION
diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
index 27f0968449de..725700ab5973 100644
--- a/drivers/cxl/core/core.h
+++ b/drivers/cxl/core/core.h
@@ -9,6 +9,13 @@ extern const struct device_type cxl_nvdimm_type;
 
 extern struct attribute_group cxl_base_attribute_group;
 
+#ifdef CONFIG_CXL_DCD
+extern struct device_attribute dev_attr_create_dc_region;
+#define SET_CXL_DC_REGION_ATTR(x) (&dev_attr_##x.attr),
+#else
+#define SET_CXL_DC_REGION_ATTR(x)
+#endif
+
 #ifdef CONFIG_CXL_REGION
 extern struct device_attribute dev_attr_create_pmem_region;
 extern struct device_attribute dev_attr_create_ram_region;
diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index 514d30131d92..29649b47d177 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -233,14 +233,23 @@ static void __cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
 	struct resource *res = cxled->dpa_res;
 	resource_size_t skip_start;
+	resource_size_t skipped = cxled->skip;
 
 	lockdep_assert_held_write(&cxl_dpa_rwsem);
 
 	/* save @skip_start, before @res is released */
-	skip_start = res->start - cxled->skip;
+	skip_start = res->start - skipped;
 	__release_region(&cxlds->dpa_res, res->start, resource_size(res));
-	if (cxled->skip)
-		__release_region(&cxlds->dpa_res, skip_start, cxled->skip);
+	if (cxled->skip != 0) {
+		while (skipped != 0) {
+			res = xa_load(&cxled->skip_res, skip_start);
+			__release_region(&cxlds->dpa_res, skip_start,
+							resource_size(res));
+			xa_erase(&cxled->skip_res, skip_start);
+			skip_start += resource_size(res);
+			skipped -= resource_size(res);
+			}
+	}
 	cxled->skip = 0;
 	cxled->dpa_res = NULL;
 	put_device(&cxled->cxld.dev);
@@ -267,6 +276,19 @@ static void devm_cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
 	__cxl_dpa_release(cxled);
 }
 
+static int dc_mode_to_region_index(enum cxl_decoder_mode mode)
+{
+	int index = 0;
+
+	for (int i = CXL_DECODER_DC0; i <= CXL_DECODER_DC7; i++) {
+		if (mode == i)
+			return index;
+		index++;
+	}
+
+	return -EINVAL;
+}
+
 static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 			     resource_size_t base, resource_size_t len,
 			     resource_size_t skipped)
@@ -275,7 +297,11 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 	struct cxl_port *port = cxled_to_port(cxled);
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
 	struct device *dev = &port->dev;
+	struct device *ed_dev = &cxled->cxld.dev;
+	struct resource *dpa_res = &cxlds->dpa_res;
+	resource_size_t skip_len = 0;
 	struct resource *res;
+	int rc, index;
 
 	lockdep_assert_held_write(&cxl_dpa_rwsem);
 
@@ -304,28 +330,119 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 	}
 
 	if (skipped) {
-		res = __request_region(&cxlds->dpa_res, base - skipped, skipped,
-				       dev_name(&cxled->cxld.dev), 0);
-		if (!res) {
-			dev_dbg(dev,
-				"decoder%d.%d: failed to reserve skipped space\n",
-				port->id, cxled->cxld.id);
-			return -EBUSY;
+		resource_size_t skip_base = base - skipped;
+
+		if (decoder_mode_is_dc(cxled->mode)) {
+			if (resource_size(&cxlds->ram_res) &&
+					skip_base <= cxlds->ram_res.end) {
+				skip_len = cxlds->ram_res.end - skip_base + 1;
+				res = __request_region(dpa_res, skip_base,
+						skip_len, dev_name(ed_dev), 0);
+				if (!res)
+					goto error;
+
+				rc = xa_insert(&cxled->skip_res, skip_base, res,
+								GFP_KERNEL);
+				skip_base += skip_len;
+			}
+
+			if (resource_size(&cxlds->ram_res) &&
+					skip_base <= cxlds->pmem_res.end) {
+				skip_len = cxlds->pmem_res.end - skip_base + 1;
+				res = __request_region(dpa_res, skip_base,
+						skip_len, dev_name(ed_dev), 0);
+				if (!res)
+					goto error;
+
+				rc = xa_insert(&cxled->skip_res, skip_base, res,
+								GFP_KERNEL);
+				skip_base += skip_len;
+			}
+
+			index = dc_mode_to_region_index(cxled->mode);
+			for (int i = 0; i <= index; i++) {
+				struct resource *dcr = &cxlds->dc_res[i];
+
+				if (skip_base < dcr->start) {
+					skip_len = dcr->start - skip_base;
+					res = __request_region(dpa_res,
+							skip_base, skip_len,
+							dev_name(ed_dev), 0);
+					if (!res)
+						goto error;
+
+					rc = xa_insert(&cxled->skip_res, skip_base,
+							res, GFP_KERNEL);
+					skip_base += skip_len;
+				}
+
+				if (skip_base == base) {
+					dev_dbg(dev, "skip done!\n");
+					break;
+				}
+
+				if (resource_size(dcr) &&
+						skip_base <= dcr->end) {
+					if (skip_base > base)
+						dev_err(dev, "Skip error\n");
+
+					skip_len = dcr->end - skip_base + 1;
+					res = __request_region(dpa_res, skip_base,
+							skip_len,
+							dev_name(ed_dev), 0);
+					if (!res)
+						goto error;
+
+					rc = xa_insert(&cxled->skip_res, skip_base,
+							res, GFP_KERNEL);
+					skip_base += skip_len;
+				}
+			}
+		} else	{
+			res = __request_region(dpa_res, base - skipped, skipped,
+							dev_name(ed_dev), 0);
+			if (!res)
+				goto error;
+
+			rc = xa_insert(&cxled->skip_res, skip_base, res,
+								GFP_KERNEL);
 		}
 	}
-	res = __request_region(&cxlds->dpa_res, base, len,
-			       dev_name(&cxled->cxld.dev), 0);
+
+	res = __request_region(dpa_res, base, len, dev_name(ed_dev), 0);
 	if (!res) {
 		dev_dbg(dev, "decoder%d.%d: failed to reserve allocation\n",
-			port->id, cxled->cxld.id);
-		if (skipped)
-			__release_region(&cxlds->dpa_res, base - skipped,
-					 skipped);
+				port->id, cxled->cxld.id);
+		if (skipped) {
+			resource_size_t skip_base = base - skipped;
+
+			while (skipped != 0) {
+				if (skip_base > base)
+					dev_err(dev, "Skip error\n");
+
+				res = xa_load(&cxled->skip_res, skip_base);
+				__release_region(dpa_res, skip_base,
+							resource_size(res));
+				xa_erase(&cxled->skip_res, skip_base);
+				skip_base += resource_size(res);
+				skipped -= resource_size(res);
+			}
+		}
 		return -EBUSY;
 	}
 	cxled->dpa_res = res;
 	cxled->skip = skipped;
 
+	for (int mode = CXL_DECODER_DC0; mode <= CXL_DECODER_DC7; mode++) {
+		int index = dc_mode_to_region_index(mode);
+
+		if (resource_contains(&cxlds->dc_res[index], res)) {
+			cxled->mode = mode;
+			dev_dbg(dev, "decoder%d.%d: %pr mode: %d\n", port->id,
+				cxled->cxld.id, cxled->dpa_res, cxled->mode);
+			goto success;
+		}
+	}
 	if (resource_contains(&cxlds->pmem_res, res))
 		cxled->mode = CXL_DECODER_PMEM;
 	else if (resource_contains(&cxlds->ram_res, res))
@@ -336,9 +453,16 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 		cxled->mode = CXL_DECODER_MIXED;
 	}
 
+success:
 	port->hdm_end++;
 	get_device(&cxled->cxld.dev);
 	return 0;
+
+error:
+	dev_dbg(dev, "decoder%d.%d: failed to reserve skipped space\n",
+			port->id, cxled->cxld.id);
+	return -EBUSY;
+
 }
 
 int devm_cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
@@ -429,6 +553,14 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
 	switch (mode) {
 	case CXL_DECODER_RAM:
 	case CXL_DECODER_PMEM:
+	case CXL_DECODER_DC0:
+	case CXL_DECODER_DC1:
+	case CXL_DECODER_DC2:
+	case CXL_DECODER_DC3:
+	case CXL_DECODER_DC4:
+	case CXL_DECODER_DC5:
+	case CXL_DECODER_DC6:
+	case CXL_DECODER_DC7:
 		break;
 	default:
 		dev_dbg(dev, "unsupported mode: %d\n", mode);
@@ -456,6 +588,16 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
 		goto out;
 	}
 
+	for (int i = CXL_DECODER_DC0; i <= CXL_DECODER_DC7; i++) {
+		int index = dc_mode_to_region_index(i);
+
+		if (mode == i && !resource_size(&cxlds->dc_res[index])) {
+			dev_dbg(dev, "no available dynamic capacity\n");
+			rc = -ENXIO;
+			goto out;
+		}
+	}
+
 	cxled->mode = mode;
 	rc = 0;
 out:
@@ -469,10 +611,12 @@ static resource_size_t cxl_dpa_freespace(struct cxl_endpoint_decoder *cxled,
 					 resource_size_t *skip_out)
 {
 	struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
-	resource_size_t free_ram_start, free_pmem_start;
+	resource_size_t free_ram_start, free_pmem_start, free_dc_start;
 	struct cxl_dev_state *cxlds = cxlmd->cxlds;
+	struct device *dev = &cxled->cxld.dev;
 	resource_size_t start, avail, skip;
 	struct resource *p, *last;
+	int index;
 
 	lockdep_assert_held(&cxl_dpa_rwsem);
 
@@ -490,6 +634,20 @@ static resource_size_t cxl_dpa_freespace(struct cxl_endpoint_decoder *cxled,
 	else
 		free_pmem_start = cxlds->pmem_res.start;
 
+	/*
+	 * One HDM Decoder per DC region to map memory with different
+	 * DSMAS entry.
+	 */
+	index = dc_mode_to_region_index(cxled->mode);
+	if (index >= 0) {
+		if (cxlds->dc_res[index].child) {
+			dev_err(dev, "Cannot allocated DPA from DC Region: %d\n",
+					index);
+			return -EINVAL;
+		}
+		free_dc_start = cxlds->dc_res[index].start;
+	}
+
 	if (cxled->mode == CXL_DECODER_RAM) {
 		start = free_ram_start;
 		avail = cxlds->ram_res.end - start + 1;
@@ -511,6 +669,29 @@ static resource_size_t cxl_dpa_freespace(struct cxl_endpoint_decoder *cxled,
 		else
 			skip_end = start - 1;
 		skip = skip_end - skip_start + 1;
+	} else if (decoder_mode_is_dc(cxled->mode)) {
+		resource_size_t skip_start, skip_end;
+
+		start = free_dc_start;
+		avail = cxlds->dc_res[index].end - start + 1;
+		if ((resource_size(&cxlds->pmem_res) == 0) || !cxlds->pmem_res.child)
+			skip_start = free_ram_start;
+		else
+			skip_start = free_pmem_start;
+		/*
+		 * If some dc region is already mapped, then that allocation
+		 * already handled the RAM and PMEM skip.Check for DC region
+		 * skip.
+		 */
+		for (int i = index - 1; i >= 0 ; i--) {
+			if (cxlds->dc_res[i].child) {
+				skip_start = cxlds->dc_res[i].child->end + 1;
+				break;
+			}
+		}
+
+		skip_end = start - 1;
+		skip = skip_end - skip_start + 1;
 	} else {
 		dev_dbg(cxled_dev(cxled), "mode not set\n");
 		avail = 0;
@@ -548,10 +729,25 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
 
 	avail = cxl_dpa_freespace(cxled, &start, &skip);
 
+	dev_dbg(dev, "DPA Allocation start: %llx len: %llx Skip: %llx\n",
+						start, size, skip);
 	if (size > avail) {
+		static const char * const names[] = {
+			[CXL_DECODER_NONE] = "none",
+			[CXL_DECODER_RAM] = "ram",
+			[CXL_DECODER_PMEM] = "pmem",
+			[CXL_DECODER_MIXED] = "mixed",
+			[CXL_DECODER_DC0] = "dc0",
+			[CXL_DECODER_DC1] = "dc1",
+			[CXL_DECODER_DC2] = "dc2",
+			[CXL_DECODER_DC3] = "dc3",
+			[CXL_DECODER_DC4] = "dc4",
+			[CXL_DECODER_DC5] = "dc5",
+			[CXL_DECODER_DC6] = "dc6",
+			[CXL_DECODER_DC7] = "dc7",
+		};
 		dev_dbg(dev, "%pa exceeds available %s capacity: %pa\n", &size,
-			cxled->mode == CXL_DECODER_RAM ? "ram" : "pmem",
-			&avail);
+			names[cxled->mode], &avail);
 		rc = -ENOSPC;
 		goto out;
 	}
diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index 5e21b53362e6..a1a98aba24ed 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -195,6 +195,22 @@ static ssize_t mode_store(struct device *dev, struct device_attribute *attr,
 		mode = CXL_DECODER_PMEM;
 	else if (sysfs_streq(buf, "ram"))
 		mode = CXL_DECODER_RAM;
+	else if (sysfs_streq(buf, "dc0"))
+		mode = CXL_DECODER_DC0;
+	else if (sysfs_streq(buf, "dc1"))
+		mode = CXL_DECODER_DC1;
+	else if (sysfs_streq(buf, "dc2"))
+		mode = CXL_DECODER_DC2;
+	else if (sysfs_streq(buf, "dc3"))
+		mode = CXL_DECODER_DC3;
+	else if (sysfs_streq(buf, "dc4"))
+		mode = CXL_DECODER_DC4;
+	else if (sysfs_streq(buf, "dc5"))
+		mode = CXL_DECODER_DC5;
+	else if (sysfs_streq(buf, "dc6"))
+		mode = CXL_DECODER_DC6;
+	else if (sysfs_streq(buf, "dc7"))
+		mode = CXL_DECODER_DC7;
 	else
 		return -EINVAL;
 
@@ -296,6 +312,7 @@ static struct attribute *cxl_decoder_root_attrs[] = {
 	&dev_attr_target_list.attr,
 	SET_CXL_REGION_ATTR(create_pmem_region)
 	SET_CXL_REGION_ATTR(create_ram_region)
+	SET_CXL_DC_REGION_ATTR(create_dc_region)
 	SET_CXL_REGION_ATTR(delete_region)
 	NULL,
 };
@@ -1691,6 +1708,7 @@ struct cxl_endpoint_decoder *cxl_endpoint_decoder_alloc(struct cxl_port *port)
 		return ERR_PTR(-ENOMEM);
 
 	cxled->pos = -1;
+	xa_init(&cxled->skip_res);
 	cxld = &cxled->cxld;
 	rc = cxl_decoder_init(port, cxld);
 	if (rc)	 {
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 543c4499379e..144232c8305e 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -1733,7 +1733,7 @@ static int cxl_region_attach(struct cxl_region *cxlr,
 	lockdep_assert_held_write(&cxl_region_rwsem);
 	lockdep_assert_held_read(&cxl_dpa_rwsem);
 
-	if (cxled->mode != cxlr->mode) {
+	if (decoder_mode_is_dc(cxlr->mode) && !decoder_mode_is_dc(cxled->mode)) {
 		dev_dbg(&cxlr->dev, "%s region mode: %d mismatch: %d\n",
 			dev_name(&cxled->cxld.dev), cxlr->mode, cxled->mode);
 		return -EINVAL;
@@ -2211,6 +2211,14 @@ static struct cxl_region *devm_cxl_add_region(struct cxl_root_decoder *cxlrd,
 	switch (mode) {
 	case CXL_DECODER_RAM:
 	case CXL_DECODER_PMEM:
+	case CXL_DECODER_DC0:
+	case CXL_DECODER_DC1:
+	case CXL_DECODER_DC2:
+	case CXL_DECODER_DC3:
+	case CXL_DECODER_DC4:
+	case CXL_DECODER_DC5:
+	case CXL_DECODER_DC6:
+	case CXL_DECODER_DC7:
 		break;
 	default:
 		dev_err(&cxlrd->cxlsd.cxld.dev, "unsupported mode %d\n", mode);
@@ -2321,6 +2329,43 @@ static ssize_t create_ram_region_store(struct device *dev,
 }
 DEVICE_ATTR_RW(create_ram_region);
 
+static ssize_t store_dcN_region(struct cxl_root_decoder *cxlrd,
+				const char *buf, enum cxl_decoder_mode mode,
+				size_t len)
+{
+	struct cxl_region *cxlr;
+	int rc, id;
+
+	rc = sscanf(buf, "region%d\n", &id);
+	if (rc != 1)
+		return -EINVAL;
+
+	cxlr = __create_region(cxlrd, id, mode, CXL_DECODER_HOSTMEM);
+	if (IS_ERR(cxlr))
+		return PTR_ERR(cxlr);
+
+	return len;
+}
+
+static ssize_t create_dc_region_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	return __create_region_show(to_cxl_root_decoder(dev), buf);
+}
+
+static ssize_t create_dc_region_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t len)
+{
+	/*
+	 * All DC regions use decoder mode DC0 as the region does not need the
+	 * index information
+	 */
+	return store_dcN_region(to_cxl_root_decoder(dev), buf,
+				CXL_DECODER_DC0, len);
+}
+DEVICE_ATTR_RW(create_dc_region);
+
 static ssize_t region_show(struct device *dev, struct device_attribute *attr,
 			   char *buf)
 {
@@ -2799,6 +2844,61 @@ static int devm_cxl_add_dax_region(struct cxl_region *cxlr)
 	return rc;
 }
 
+static void cxl_dc_region_release(void *data)
+{
+	struct cxl_region *cxlr = data;
+	struct cxl_dc_region *cxlr_dc = cxlr->cxlr_dc;
+
+	xa_destroy(&cxlr_dc->dax_dev_list);
+	kfree(cxlr_dc);
+}
+
+static int devm_cxl_add_dc_region(struct cxl_region *cxlr)
+{
+	struct cxl_dc_region *cxlr_dc;
+	struct cxl_dax_region *cxlr_dax;
+	struct device *dev;
+	int rc = 0;
+
+	cxlr_dax = cxl_dax_region_alloc(cxlr);
+	if (IS_ERR(cxlr_dax))
+		return PTR_ERR(cxlr_dax);
+
+	cxlr_dc = kzalloc(sizeof(*cxlr_dc), GFP_KERNEL);
+	if (!cxlr_dc) {
+		rc = -ENOMEM;
+		goto err;
+	}
+
+	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));
+
+	rc = devm_add_action_or_reset(&cxlr->dev, cxlr_dax_unregister,
+					cxlr_dax);
+	if (rc)
+		goto err;
+
+	cxlr_dc->cxlr_dax = cxlr_dax;
+	xa_init(&cxlr_dc->dax_dev_list);
+	cxlr->cxlr_dc = cxlr_dc;
+	rc = devm_add_action_or_reset(&cxlr->dev, cxl_dc_region_release, cxlr);
+	if (!rc)
+		return 0;
+err:
+	put_device(dev);
+	kfree(cxlr_dc);
+	return rc;
+}
+
 static int match_decoder_by_range(struct device *dev, void *data)
 {
 	struct range *r1, *r2 = data;
@@ -3140,6 +3240,19 @@ static int is_system_ram(struct resource *res, void *arg)
 	return 1;
 }
 
+/*
+ * The region can not be manged by CXL if any portion of
+ * it is already online as 'System RAM'
+ */
+static bool region_is_system_ram(struct cxl_region *cxlr,
+				 struct cxl_region_params *p)
+{
+	return (walk_iomem_res_desc(IORES_DESC_NONE,
+				    IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY,
+				    p->res->start, p->res->end, cxlr,
+				    is_system_ram) > 0);
+}
+
 static int cxl_region_probe(struct device *dev)
 {
 	struct cxl_region *cxlr = to_cxl_region(dev);
@@ -3174,14 +3287,7 @@ static int cxl_region_probe(struct device *dev)
 	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)
+		if (region_is_system_ram(cxlr, p))
 			return 0;
 
 		/*
@@ -3193,6 +3299,17 @@ static int cxl_region_probe(struct device *dev)
 
 		/* HDM-H routes to device-dax */
 		return devm_cxl_add_dax_region(cxlr);
+	case CXL_DECODER_DC0:
+	case CXL_DECODER_DC1:
+	case CXL_DECODER_DC2:
+	case CXL_DECODER_DC3:
+	case CXL_DECODER_DC4:
+	case CXL_DECODER_DC5:
+	case CXL_DECODER_DC6:
+	case CXL_DECODER_DC7:
+		if (region_is_system_ram(cxlr, p))
+			return 0;
+		return devm_cxl_add_dc_region(cxlr);
 	default:
 		dev_dbg(&cxlr->dev, "unsupported region mode: %d\n",
 			cxlr->mode);
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 8400af85d99f..7ac1237938b7 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -335,6 +335,14 @@ enum cxl_decoder_mode {
 	CXL_DECODER_NONE,
 	CXL_DECODER_RAM,
 	CXL_DECODER_PMEM,
+	CXL_DECODER_DC0,
+	CXL_DECODER_DC1,
+	CXL_DECODER_DC2,
+	CXL_DECODER_DC3,
+	CXL_DECODER_DC4,
+	CXL_DECODER_DC5,
+	CXL_DECODER_DC6,
+	CXL_DECODER_DC7,
 	CXL_DECODER_MIXED,
 	CXL_DECODER_DEAD,
 };
@@ -345,6 +353,14 @@ static inline const char *cxl_decoder_mode_name(enum cxl_decoder_mode mode)
 		[CXL_DECODER_NONE] = "none",
 		[CXL_DECODER_RAM] = "ram",
 		[CXL_DECODER_PMEM] = "pmem",
+		[CXL_DECODER_DC0] = "dc0",
+		[CXL_DECODER_DC1] = "dc1",
+		[CXL_DECODER_DC2] = "dc2",
+		[CXL_DECODER_DC3] = "dc3",
+		[CXL_DECODER_DC4] = "dc4",
+		[CXL_DECODER_DC5] = "dc5",
+		[CXL_DECODER_DC6] = "dc6",
+		[CXL_DECODER_DC7] = "dc7",
 		[CXL_DECODER_MIXED] = "mixed",
 	};
 
@@ -353,6 +369,11 @@ static inline const char *cxl_decoder_mode_name(enum cxl_decoder_mode mode)
 	return "mixed";
 }
 
+static inline bool decoder_mode_is_dc(enum cxl_decoder_mode mode)
+{
+	return (mode >= CXL_DECODER_DC0 && mode <= CXL_DECODER_DC7);
+}
+
 /*
  * Track whether this decoder is reserved for region autodiscovery, or
  * free for userspace provisioning.
@@ -375,6 +396,7 @@ struct cxl_endpoint_decoder {
 	struct cxl_decoder cxld;
 	struct resource *dpa_res;
 	resource_size_t skip;
+	struct xarray skip_res;
 	enum cxl_decoder_mode mode;
 	enum cxl_decoder_state state;
 	int pos;
@@ -475,6 +497,11 @@ struct cxl_region_params {
  */
 #define CXL_REGION_F_AUTO 1
 
+struct cxl_dc_region {
+	struct xarray dax_dev_list;
+	struct cxl_dax_region *cxlr_dax;
+};
+
 /**
  * struct cxl_region - CXL region
  * @dev: This region's device
@@ -493,6 +520,7 @@ struct cxl_region {
 	enum cxl_decoder_type type;
 	struct cxl_nvdimm_bridge *cxl_nvb;
 	struct cxl_pmem_region *cxlr_pmem;
+	struct cxl_dc_region *cxlr_dc;
 	unsigned long flags;
 	struct cxl_region_params params;
 };
diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
index ccdf8de85bd5..eb5eb81bfbd7 100644
--- a/drivers/dax/cxl.c
+++ b/drivers/dax/cxl.c
@@ -23,11 +23,15 @@ static int cxl_dax_region_probe(struct device *dev)
 	if (!dax_region)
 		return -ENOMEM;
 
+	if (decoder_mode_is_dc(cxlr->mode))
+		return 0;
+
 	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);

-- 
2.40.0