netdev - [PATCH v16 19/22] cxl: Add region flag for precluding a device memory to be used for dax

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Message-ID: <20250514132743.523469-20-alejandro.lucero-palau@amd.com>
Date: Wed, 14 May 2025 14:27:40 +0100
From: <alejandro.lucero-palau@....com>
To: <linux-cxl@...r.kernel.org>, <netdev@...r.kernel.org>,
	<dan.j.williams@...el.com>, <edward.cree@....com>, <davem@...emloft.net>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <edumazet@...gle.com>,
	<dave.jiang@...el.com>
CC: Alejandro Lucero <alucerop@....com>, Zhi Wang <zhiw@...dia.com>, "Jonathan
 Cameron" <Jonathan.Cameron@...wei.com>, Ben Cheatham
	<benjamin.cheatham@....com>
Subject: [PATCH v16 19/22] cxl: Add region flag for precluding a device memory to be used for dax

From: Alejandro Lucero <alucerop@....com>

By definition a type2 cxl device will use the host managed memory for
specific functionality, therefore it should not be available to other
uses. However, a dax interface could be just good enough in some cases.

Add a flag to a cxl region for specifically state to not create a dax
device. Allow a Type2 driver to set that flag at region creation time.

Signed-off-by: Alejandro Lucero <alucerop@....com>
Reviewed-by: Zhi Wang <zhiw@...dia.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Reviewed-by: Ben Cheatham <benjamin.cheatham@....com>
Reviewed-by: Dave Jiang <dave.jiang@...el.com>
---
 drivers/cxl/core/region.c | 10 +++++++++-
 drivers/cxl/cxl.h         |  3 +++
 include/cxl/cxl.h         |  3 ++-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index f82da914d125..06647bae210f 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -3658,12 +3658,14 @@ __construct_new_region(struct cxl_root_decoder *cxlrd,
  * @cxlrd: root decoder to allocate HPA
  * @cxled: endpoint decoder with reserved DPA capacity
  * @ways: interleave ways required
+ * @no_dax: if true no DAX device should be created
  *
  * Returns a fully formed region in the commit state and attached to the
  * cxl_region driver.
  */
 struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
-				     struct cxl_endpoint_decoder *cxled, int ways)
+				     struct cxl_endpoint_decoder *cxled, int ways,
+				     bool no_dax)
 {
 	struct cxl_region *cxlr;
 
@@ -3679,6 +3681,9 @@ struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
 		return ERR_PTR(-ENODEV);
 	}
 
+	if (no_dax)
+		set_bit(CXL_REGION_F_NO_DAX, &cxlr->flags);
+
 	return cxlr;
 }
 EXPORT_SYMBOL_NS_GPL(cxl_create_region, "CXL");
@@ -3842,6 +3847,9 @@ static int cxl_region_probe(struct device *dev)
 	if (rc)
 		return rc;
 
+	if (test_bit(CXL_REGION_F_NO_DAX, &cxlr->flags))
+		return 0;
+
 	switch (cxlr->mode) {
 	case CXL_PARTMODE_PMEM:
 		return devm_cxl_add_pmem_region(cxlr);
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 6fc6fd7b571d..8c418d62b0e4 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -405,6 +405,9 @@ struct cxl_region_params {
  */
 #define CXL_REGION_F_NEEDS_RESET 1
 
+/* Allow Type2 drivers to specify if a dax region should not be created. */
+#define CXL_REGION_F_NO_DAX 2
+
 /**
  * struct cxl_region - CXL region
  * @dev: This region's device
diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
index d9cd10537fb1..867dd33adaff 100644
--- a/include/cxl/cxl.h
+++ b/include/cxl/cxl.h
@@ -283,7 +283,8 @@ struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
 					     resource_size_t alloc);
 int cxl_dpa_free(struct cxl_endpoint_decoder *cxled);
 struct cxl_region *cxl_create_region(struct cxl_root_decoder *cxlrd,
-				     struct cxl_endpoint_decoder *cxled, int ways);
+				     struct cxl_endpoint_decoder *cxled, int ways,
+				     bool no_dax);
 
 int cxl_accel_region_detach(struct cxl_endpoint_decoder *cxled);
 #endif /* __CXL_CXL_H__ */
-- 
2.34.1