cxl/acpi: Move rescan to the workqueue

Now that the cxl_mem driver has a need to take the root device lock, the
cxl_bus_rescan() needs to run outside of the root lock context. That
need arises from RCH topologies and the locking that the cxl_mem driver
does to attach a descendant to an upstream port. In the RCH case the
lock needed is the CXL root device lock [1].

Link: http://lore.kernel.org/r/166993045621.1882361.1730100141527044744.stgit@dwillia2-xfh.jf.intel.com [1]
Tested-by: Robert Richter <rrichter@amd.com>
Link: http://lore.kernel.org/r/166993042884.1882361.5633723613683058881.stgit@dwillia2-xfh.jf.intel.comReviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/acpi.c

@@ -511,7 +511,8 @@ static int cxl_acpi_probe(struct platform_device *pdev)
 		return rc;
 
 	/* In case PCI is scanned before ACPI re-trigger memdev attach */
-	return cxl_bus_rescan();
+	cxl_bus_rescan();
+	return 0;
 }
 
 static const struct acpi_device_id cxl_acpi_ids[] = {
@@ -535,7 +536,19 @@ static struct platform_driver cxl_acpi_driver = {
 	.id_table = cxl_test_ids,
 };
 
-module_platform_driver(cxl_acpi_driver);
+static int __init cxl_acpi_init(void)
+{
+	return platform_driver_register(&cxl_acpi_driver);
+}
+
+static void __exit cxl_acpi_exit(void)
+{
+	platform_driver_unregister(&cxl_acpi_driver);
+	cxl_bus_drain();
+}
+
+module_init(cxl_acpi_init);
+module_exit(cxl_acpi_exit);
 MODULE_LICENSE("GPL v2");
 MODULE_IMPORT_NS(CXL);
 MODULE_IMPORT_NS(ACPI);

drivers/cxl/core/port.c

@@ -1844,12 +1844,27 @@ static void cxl_bus_remove(struct device *dev)
 
 static struct workqueue_struct *cxl_bus_wq;
 
-int cxl_bus_rescan(void)
+static void cxl_bus_rescan_queue(struct work_struct *w)
 {
-	return bus_rescan_devices(&cxl_bus_type);
+	int rc = bus_rescan_devices(&cxl_bus_type);
+
+	pr_debug("CXL bus rescan result: %d\n", rc);
+}
+
+void cxl_bus_rescan(void)
+{
+	static DECLARE_WORK(rescan_work, cxl_bus_rescan_queue);
+
+	queue_work(cxl_bus_wq, &rescan_work);
 }
 EXPORT_SYMBOL_NS_GPL(cxl_bus_rescan, CXL);
 
+void cxl_bus_drain(void)
+{
+	drain_workqueue(cxl_bus_wq);
+}
+EXPORT_SYMBOL_NS_GPL(cxl_bus_drain, CXL);
+
 bool schedule_cxl_memdev_detach(struct cxl_memdev *cxlmd)
 {
 	return queue_work(cxl_bus_wq, &cxlmd->detach_work);

drivers/cxl/cxl.h

@@ -552,7 +552,8 @@ int devm_cxl_add_endpoint(struct cxl_memdev *cxlmd,
 			  struct cxl_dport *parent_dport);
 struct cxl_port *find_cxl_root(struct device *dev);
 int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd);
-int cxl_bus_rescan(void);
+void cxl_bus_rescan(void);
+void cxl_bus_drain(void);
 struct cxl_port *cxl_mem_find_port(struct cxl_memdev *cxlmd,
 				   struct cxl_dport **dport);
 bool schedule_cxl_memdev_detach(struct cxl_memdev *cxlmd);