linux-kernel - [PATCH 7/9] cxl/core: add cxl_devdax_region driver for explicit userland region binding

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Message-ID: <20260129210442.3951412-8-gourry@gourry.net>
Date: Thu, 29 Jan 2026 16:04:40 -0500
From: Gregory Price <gourry@...rry.net>
To: linux-mm@...ck.org
Cc: linux-cxl@...r.kernel.org,
	nvdimm@...ts.linux.dev,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	kernel-team@...a.com,
	dave@...olabs.net,
	jonathan.cameron@...wei.com,
	dave.jiang@...el.com,
	alison.schofield@...el.com,
	vishal.l.verma@...el.com,
	ira.weiny@...el.com,
	dan.j.williams@...el.com,
	willy@...radead.org,
	jack@...e.cz,
	terry.bowman@....com,
	john@...alactic.com
Subject: [PATCH 7/9] cxl/core: add cxl_devdax_region driver for explicit userland region binding

Add a new cxl_devdax_region driver that probes CXL regions in device
dax mode and creates dax_region devices. This allows explicit binding to
the device_dax dax driver instead of the kmem driver.

Exports to_cxl_region() to core.h so it can be used by the driver.

Signed-off-by: Gregory Price <gourry@...rry.net>
---
 drivers/cxl/core/core.h       |  2 ++
 drivers/cxl/core/dax_region.c | 16 ++++++++++++++++
 drivers/cxl/core/region.c     | 21 +++++++++++++++++----
 drivers/cxl/cxl.h             |  1 +
 4 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
index 217dd708a2a6..ea4df8abc2ad 100644
--- a/drivers/cxl/core/core.h
+++ b/drivers/cxl/core/core.h
@@ -46,6 +46,8 @@ u64 cxl_dpa_to_hpa(struct cxl_region *cxlr, const struct cxl_memdev *cxlmd,
 int devm_cxl_add_dax_region(struct cxl_region *cxlr, enum dax_driver_type);
 int devm_cxl_add_pmem_region(struct cxl_region *cxlr);
 
+extern struct cxl_driver cxl_devdax_region_driver;
+
 #else
 static inline u64 cxl_dpa_to_hpa(struct cxl_region *cxlr,
 				 const struct cxl_memdev *cxlmd, u64 dpa)
diff --git a/drivers/cxl/core/dax_region.c b/drivers/cxl/core/dax_region.c
index 0602db5f7248..391d51e5ec37 100644
--- a/drivers/cxl/core/dax_region.c
+++ b/drivers/cxl/core/dax_region.c
@@ -111,3 +111,19 @@ int devm_cxl_add_dax_region(struct cxl_region *cxlr,
 	put_device(dev);
 	return rc;
 }
+
+static int cxl_devdax_region_driver_probe(struct device *dev)
+{
+	struct cxl_region *cxlr = to_cxl_region(dev);
+
+	if (cxlr->mode != CXL_PARTMODE_RAM)
+		return -ENODEV;
+
+	return devm_cxl_add_dax_region(cxlr, DAXDRV_DEVICE_TYPE);
+}
+
+struct cxl_driver cxl_devdax_region_driver = {
+	.name = "cxl_devdax_region",
+	.probe = cxl_devdax_region_driver_probe,
+	.id = CXL_DEVICE_REGION,
+};
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 61ec939c1462..6200ca1cc2dd 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -39,8 +39,6 @@
  */
 static nodemask_t nodemask_region_seen = NODE_MASK_NONE;
 
-static struct cxl_region *to_cxl_region(struct device *dev);
-
 #define __ACCESS_ATTR_RO(_level, _name) {				\
 	.attr	= { .name = __stringify(_name), .mode = 0444 },		\
 	.show	= _name##_access##_level##_show,			\
@@ -2430,7 +2428,7 @@ bool is_cxl_region(struct device *dev)
 }
 EXPORT_SYMBOL_NS_GPL(is_cxl_region, "CXL");
 
-static struct cxl_region *to_cxl_region(struct device *dev)
+struct cxl_region *to_cxl_region(struct device *dev)
 {
 	if (dev_WARN_ONCE(dev, dev->type != &cxl_region_type,
 			  "not a cxl_region device\n"))
@@ -3726,11 +3724,26 @@ static struct cxl_driver cxl_region_driver = {
 
 int cxl_region_init(void)
 {
-	return cxl_driver_register(&cxl_region_driver);
+	int rc;
+
+	rc = cxl_driver_register(&cxl_region_driver);
+	if (rc)
+		return rc;
+
+	rc = cxl_driver_register(&cxl_devdax_region_driver);
+	if (rc)
+		goto err_dax;
+
+	return 0;
+
+err_dax:
+	cxl_driver_unregister(&cxl_region_driver);
+	return rc;
 }
 
 void cxl_region_exit(void)
 {
+	cxl_driver_unregister(&cxl_devdax_region_driver);
 	cxl_driver_unregister(&cxl_region_driver);
 }
 
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index c06a239c0008..674d5f870c70 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -859,6 +859,7 @@ int cxl_dvsec_rr_decode(struct cxl_dev_state *cxlds,
 			struct cxl_endpoint_dvsec_info *info);
 
 bool is_cxl_region(struct device *dev);
+struct cxl_region *to_cxl_region(struct device *dev);
 
 extern const struct bus_type cxl_bus_type;
 
-- 
2.52.0