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, 101 insertions, 4 deletions

diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index c5779c982c80..f460460b12b3 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright(c) 2020 Intel Corporation. All rights reserved. */
 #include <linux/io-64-nonatomic-lo-hi.h>
+#include <linux/workqueue.h>
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/pci.h>
@@ -46,6 +47,8 @@ static int cxl_device_id(struct device *dev)
 			return CXL_DEVICE_ROOT;
 		return CXL_DEVICE_PORT;
 	}
+	if (is_cxl_memdev(dev))
+		return CXL_DEVICE_MEMORY_EXPANDER;
 	return 0;
 }
 
@@ -318,8 +321,10 @@ static void unregister_port(void *_port)
 {
 	struct cxl_port *port = _port;
 
-	if (!is_cxl_root(port))
+	if (!is_cxl_root(port)) {
 		device_lock_assert(port->dev.parent);
+		port->uport = NULL;
+	}
 
 	device_unregister(&port->dev);
 }
@@ -410,7 +415,9 @@ struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
 	if (parent_port)
 		port->depth = parent_port->depth + 1;
 	dev = &port->dev;
-	if (parent_port)
+	if (is_cxl_memdev(uport))
+		rc = dev_set_name(dev, "endpoint%d", port->id);
+	else if (parent_port)
 		rc = dev_set_name(dev, "port%d", port->id);
 	else
 		rc = dev_set_name(dev, "root%d", port->id);
@@ -790,6 +797,38 @@ static struct device *grandparent(struct device *dev)
 	return NULL;
 }
 
+static void delete_endpoint(void *data)
+{
+	struct cxl_memdev *cxlmd = data;
+	struct cxl_port *endpoint = dev_get_drvdata(&cxlmd->dev);
+	struct cxl_port *parent_port;
+	struct device *parent;
+
+	parent_port = cxl_mem_find_port(cxlmd);
+	if (!parent_port)
+		return;
+	parent = &parent_port->dev;
+
+	cxl_device_lock(parent);
+	if (parent->driver && endpoint->uport) {
+		devm_release_action(parent, cxl_unlink_uport, endpoint);
+		devm_release_action(parent, unregister_port, endpoint);
+	}
+	cxl_device_unlock(parent);
+	put_device(parent);
+	put_device(&endpoint->dev);
+}
+
+int cxl_endpoint_autoremove(struct cxl_memdev *cxlmd, struct cxl_port *endpoint)
+{
+	struct device *dev = &cxlmd->dev;
+
+	get_device(&endpoint->dev);
+	dev_set_drvdata(dev, endpoint);
+	return devm_add_action_or_reset(dev, delete_endpoint, cxlmd);
+}
+EXPORT_SYMBOL_NS_GPL(cxl_endpoint_autoremove, CXL);
+
 /*
  * The natural end of life of a non-root 'cxl_port' is when its parent port goes
  * through a ->remove() event ("top-down" unregistration). The unnatural trigger
@@ -1034,6 +1073,12 @@ retry:
 }
 EXPORT_SYMBOL_NS_GPL(devm_cxl_enumerate_ports, CXL);
 
+struct cxl_port *cxl_mem_find_port(struct cxl_memdev *cxlmd)
+{
+	return find_cxl_port(grandparent(&cxlmd->dev));
+}
+EXPORT_SYMBOL_NS_GPL(cxl_mem_find_port, CXL);
+
 struct cxl_dport *cxl_find_dport_by_dev(struct cxl_port *port,
 					const struct device *dev)
 {
@@ -1352,12 +1397,54 @@ static void cxl_bus_remove(struct device *dev)
 	cxl_nested_unlock(dev);
 }
 
+static struct workqueue_struct *cxl_bus_wq;
+
+int cxl_bus_rescan(void)
+{
+	return bus_rescan_devices(&cxl_bus_type);
+}
+EXPORT_SYMBOL_NS_GPL(cxl_bus_rescan, CXL);
+
+bool schedule_cxl_memdev_detach(struct cxl_memdev *cxlmd)
+{
+	return queue_work(cxl_bus_wq, &cxlmd->detach_work);
+}
+EXPORT_SYMBOL_NS_GPL(schedule_cxl_memdev_detach, CXL);
+
+/* for user tooling to ensure port disable work has completed */
+static ssize_t flush_store(struct bus_type *bus, const char *buf, size_t count)
+{
+	if (sysfs_streq(buf, "1")) {
+		flush_workqueue(cxl_bus_wq);
+		return count;
+	}
+
+	return -EINVAL;
+}
+
+static BUS_ATTR_WO(flush);
+
+static struct attribute *cxl_bus_attributes[] = {
+	&bus_attr_flush.attr,
+	NULL,
+};
+
+static struct attribute_group cxl_bus_attribute_group = {
+	.attrs = cxl_bus_attributes,
+};
+
+static const struct attribute_group *cxl_bus_attribute_groups[] = {
+	&cxl_bus_attribute_group,
+	NULL,
+};
+
 struct bus_type cxl_bus_type = {
 	.name = "cxl",
 	.uevent = cxl_bus_uevent,
 	.match = cxl_bus_match,
 	.probe = cxl_bus_probe,
 	.remove = cxl_bus_remove,
+	.bus_groups = cxl_bus_attribute_groups,
 };
 EXPORT_SYMBOL_NS_GPL(cxl_bus_type, CXL);
 
@@ -1371,12 +1458,21 @@ static __init int cxl_core_init(void)
 	if (rc)
 		return rc;
 
+	cxl_bus_wq = alloc_ordered_workqueue("cxl_port", 0);
+	if (!cxl_bus_wq) {
+		rc = -ENOMEM;
+		goto err_wq;
+	}
+
 	rc = bus_register(&cxl_bus_type);
 	if (rc)
-		goto err;
+		goto err_bus;
+
 	return 0;
 
-err:
+err_bus:
+	destroy_workqueue(cxl_bus_wq);
+err_wq:
 	cxl_memdev_exit();
 	cxl_mbox_exit();
 	return rc;
@@ -1385,6 +1481,7 @@ err:
 static void cxl_core_exit(void)
 {
 	bus_unregister(&cxl_bus_type);
+	destroy_workqueue(cxl_bus_wq);
 	cxl_memdev_exit();
 	cxl_mbox_exit();
 }