cxl/mem: Add the cxl_mem driver

At this point the subsystem can enumerate all CXL ports (CXL.mem decode
resources in upstream switch ports and host bridges) in a system. The
last mile is connecting those ports to endpoints.

The cxl_mem driver connects an endpoint device to the platform CXL.mem
protoctol decode-topology. At ->probe() time it walks its
device-topology-ancestry and adds a CXL Port object at every Upstream
Port hop until it gets to CXL root. The CXL root object is only present
after a platform firmware driver registers platform CXL resources. For
ACPI based platform this is managed by the ACPI0017 device and the
cxl_acpi driver.

The ports are registered such that disabling a given port automatically
unregisters all descendant ports, and the chain can only be registered
after the root is established.

Given ACPI device scanning may run asynchronously compared to PCI device
scanning the root driver is tasked with rescanning the bus after the
root successfully probes.

Conversely if any ports in a chain between the root and an endpoint
becomes disconnected it subsequently triggers the endpoint to
unregister. Given lock depenedencies the endpoint unregistration happens
in a workqueue asynchronously. If userspace cares about synchronizing
delayed work after port events the /sys/bus/cxl/flush attribute is
available for that purpose.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
[djbw: clarify changelog, rework hotplug support]
Link: https://lore.kernel.org/r/164398782997.903003.9725273241627693186.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index b2773664e407..1f76b28f9826 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -162,6 +162,12 @@ static const struct device_type cxl_memdev_type = {
 	.groups = cxl_memdev_attribute_groups,
 };
 
+bool is_cxl_memdev(struct device *dev)
+{
+	return dev->type == &cxl_memdev_type;
+}
+EXPORT_SYMBOL_NS_GPL(is_cxl_memdev, CXL);
+
 /**
  * set_exclusive_cxl_commands() - atomically disable user cxl commands
  * @cxlds: The device state to operate on
@@ -213,6 +219,15 @@ static void cxl_memdev_unregister(void *_cxlmd)
 	put_device(dev);
 }
 
+static void detach_memdev(struct work_struct *work)
+{
+	struct cxl_memdev *cxlmd;
+
+	cxlmd = container_of(work, typeof(*cxlmd), detach_work);
+	device_release_driver(&cxlmd->dev);
+	put_device(&cxlmd->dev);
+}
+
 static struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds,
 					   const struct file_operations *fops)
 {
@@ -237,6 +252,7 @@ static struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds,
 	dev->devt = MKDEV(cxl_mem_major, cxlmd->id);
 	dev->type = &cxl_memdev_type;
 	device_set_pm_not_required(dev);
+	INIT_WORK(&cxlmd->detach_work, detach_memdev);
 
 	cdev = &cxlmd->cdev;
 	cdev_init(cdev, fops);