[PATCH v2 2/6] cxl/mem: Arrange for always-synchronous memdev attach

Dan Williams
2025-12-16T00:55:34Z

In preparation for CXL accelerator drivers that have a hard dependency on
CXL capability initialization, arrange for cxl_mem_probe() to always run
synchronous with the device_add() of cxl_memdev instances. I.e.
cxl_mem_driver registration is always complete before the first memdev
creation event.

At present, cxl_pci does not care about the attach state of the cxl_memdev
because all generic memory expansion functionality can be handled by the
cxl_core. For accelerators, however, that driver needs to perform driver
specific initialization if CXL is available, or execute a fallback to PCIe
only operation.

This synchronous attach guarantee is also needed for Soft Reserve Recovery,
which is an effort that needs to assert that devices have had a chance to
attach before making a go / no-go decision on proceeding with CXL subsystem
initialization.

By moving devm_cxl_add_memdev() to cxl_mem.ko it removes async module
loading as one reason that a memdev may not be attached upon return from
devm_cxl_add_memdev().

Cc: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
Cc: Alejandro Lucero <alucerop@amd.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Tested-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Ben Cheatham <benjamin.cheatham@amd.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Alejandro Lucero <alucerop@amd.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/cxl/Kconfig | 2 +-
drivers/cxl/cxlmem.h | 2 ++
drivers/cxl/core/memdev.c | 10 +++++++---
drivers/cxl/mem.c | 17 +++++++++++++++++
4 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index 48b7314afdb8..f1361ed6a0d4 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -22,6 +22,7 @@ if CXL_BUS
config CXL_PCI
tristate "PCI manageability"
default CXL_BUS
+ select CXL_MEM
help
The CXL specification defines a "CXL memory device" sub-class in the
PCI "memory controller" base class of devices. Device's identified by
@@ -89,7 +90,6 @@ config CXL_PMEM

config CXL_MEM
tristate "CXL: Memory Expansion"
- depends on CXL_PCI
default CXL_BUS
help
The CXL.mem protocol allows a device to act as a provider of "System
diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
index c12ab4fc9512..012e68acad34 100644
--- a/drivers/cxl/cxlmem.h
+++ b/drivers/cxl/cxlmem.h
@@ -95,6 +95,8 @@ static inline bool is_cxl_endpoint(struct cxl_port *port)
return is_cxl_memdev(port->uport_dev);
}

+struct cxl_memdev *__devm_cxl_add_memdev(struct device *host,
+ struct cxl_dev_state *cxlds);
struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
struct cxl_dev_state *cxlds);
int devm_cxl_sanitize_setup_notifier(struct device *host,
diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index 4dff7f44d908..7a4153e1c6a7 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -1050,8 +1050,12 @@ static const struct file_operations cxl_memdev_fops = {
.llseek = noop_llseek,
};

-struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
- struct cxl_dev_state *cxlds)
+/*
+ * Core helper for devm_cxl_add_memdev() that wants to both create a device and
+ * assert to the caller that upon return cxl_mem::probe() has been invoked.
+ */
+struct cxl_memdev *__devm_cxl_add_memdev(struct device *host,
+ struct cxl_dev_state *cxlds)
{
struct cxl_memdev *cxlmd;
struct device *dev;
@@ -1093,7 +1097,7 @@ struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
put_device(dev);
return ERR_PTR(rc);
}
-EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");
+EXPORT_SYMBOL_FOR_MODULES(__devm_cxl_add_memdev, "cxl_mem");

static void sanitize_teardown_notifier(void *data)
{
diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index 6e6777b7bafb..55883797ab2d 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -201,6 +201,22 @@ static int cxl_mem_probe(struct device *dev)
return devm_add_action_or_reset(dev, enable_suspend, NULL);
}

+/**
+ * devm_cxl_add_memdev - Add a CXL memory device
+ * @host: devres alloc/release context and parent for the memdev
+ * @cxlds: CXL device state to associate with the memdev
+ *
+ * Upon return the device will have had a chance to attach to the
+ * cxl_mem driver, but may fail if the CXL topology is not ready
+ * (hardware CXL link down, or software platform CXL root not attached)
+ */
+struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
+ struct cxl_dev_state *cxlds)
+{
+ return __devm_cxl_add_memdev(host, cxlds);
+}
+EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");
+
static ssize_t trigger_poison_list_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t len)
@@ -248,6 +264,7 @@ static struct cxl_driver cxl_mem_driver = {
.probe = cxl_mem_probe,
.id = CXL_DEVICE_MEMORY_EXPANDER,
.drv = {
+ .probe_type = PROBE_FORCE_SYNCHRONOUS,
.dev_groups = cxl_mem_groups,
},
};
--
2.51.1