[RFC PATCH 07/13] cxl: add functions for exclusive access to endpoint port topology

[<alucerop@amd.com>]

From: Alejandro Lucero <alucerop@amd.com>

Prevent concurrent access to endpoint port topology.

Signed-off-by: Alejandro Lucero <alucerop@amd.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/cxl/core/memdev.c           | 41 +++++++++++++++++++++++++++++
 include/linux/cxlmem.h              |  4 +++
 tools/testing/cxl/type2/pci_type2.c |  9 +++++++
 3 files changed, 54 insertions(+)

diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index 27063cd4ea73..16e356ef5b6d 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -1124,6 +1124,47 @@ struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
 }
 EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, CXL);
 
+/*
+ * Try to get a locked reference on a memdev's CXL port topology
+ * connection. Be careful to observe when cxl_mem_probe() has deposited
+ * a probe deferral awaiting the arrival of the CXL root driver
+*/
+struct cxl_port *cxl_acquire_endpoint(struct cxl_memdev *cxlmd)
+{
+	struct cxl_port *endpoint;
+	int rc = -ENXIO;
+
+	device_lock(&cxlmd->dev);
+	endpoint = cxlmd->endpoint;
+	if (!endpoint)
+		goto err;
+
+	if (IS_ERR(endpoint)) {
+		rc = PTR_ERR(endpoint);
+		goto err;
+	}
+
+	device_lock(&endpoint->dev);
+	if (!endpoint->dev.driver)
+		goto err_endpoint;
+
+	return endpoint;
+
+err_endpoint:
+	device_unlock(&endpoint->dev);
+err:
+	device_unlock(&cxlmd->dev);
+	return ERR_PTR(rc);
+}
+EXPORT_SYMBOL_NS(cxl_acquire_endpoint, CXL);
+
+void cxl_release_endpoint(struct cxl_memdev *cxlmd, struct cxl_port *endpoint)
+{
+	device_unlock(&endpoint->dev);
+	device_unlock(&cxlmd->dev);
+}
+EXPORT_SYMBOL_NS(cxl_release_endpoint, CXL);
+
 static void sanitize_teardown_notifier(void *data)
 {
 	struct cxl_memdev_state *mds = data;
diff --git a/include/linux/cxlmem.h b/include/linux/cxlmem.h
index e8d12b543db1..11fe8367b046 100644
--- a/include/linux/cxlmem.h
+++ b/include/linux/cxlmem.h
@@ -88,6 +88,10 @@ static inline bool is_cxl_endpoint(struct cxl_port *port)
 
 struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
 				       struct cxl_dev_state *cxlds);
+
+struct cxl_port *cxl_acquire_endpoint(struct cxl_memdev *cxlmd);
+void cxl_release_endpoint(struct cxl_memdev *cxlmd, struct cxl_port *endpoint);
+
 int devm_cxl_sanitize_setup_notifier(struct device *host,
 				     struct cxl_memdev *cxlmd);
 struct cxl_memdev_state;
diff --git a/tools/testing/cxl/type2/pci_type2.c b/tools/testing/cxl/type2/pci_type2.c
index f157139b712f..948cc95c5780 100644
--- a/tools/testing/cxl/type2/pci_type2.c
+++ b/tools/testing/cxl/type2/pci_type2.c
@@ -6,6 +6,7 @@
 
 struct cxl_dev_state *cxlds;
 struct cxl_memdev *cxlmd;
+struct cxl_port *endpoint;
 
 #define CXL_TYPE2_MEM_SIZE   (1024*1024*256)
 
@@ -72,6 +73,14 @@ static int type2_pci_probe(struct pci_dev *pci_dev,
 	if (IS_ERR(cxlmd))
 		return PTR_ERR(cxlmd);
 
+	endpoint = cxl_acquire_endpoint(cxlmd);
+	if (IS_ERR(endpoint)) {
+		dev_dbg(&pci_dev->dev, "cxl_acquire_endpoint failed\n");
+		return PTR_ERR(endpoint);
+	}
+
+	cxl_release_endpoint(cxlmd, endpoint);
+
 	return 0;
 }
 
-- 
2.17.1