cxl/pmem: Add initial infrastructure for pmem support

Register an 'nvdimm-bridge' device to act as an anchor for a libnvdimm
bus hierarchy. Also, flesh out the cxl_bus definition to allow a
cxl_nvdimm_bridge_driver to attach to the bridge and trigger the
nvdimm-bus registration.

The creation of the bridge is gated on the detection of a PMEM capable
address space registered to the root. The bridge indirection allows the
libnvdimm module to remain unloaded on platforms without PMEM support.

Given that the probing of ACPI0017 is asynchronous to CXL endpoint
devices, and the expectation that CXL endpoint devices register other
PMEM resources on the 'CXL' nvdimm bus, a workqueue is added. The
workqueue is needed to run bus_rescan_devices() outside of the
device_lock() of the nvdimm-bridge device to rendezvous nvdimm resources
as they arrive. For now only the bus is taken online/offline in the
workqueue.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/162379909706.2993820.14051258608641140169.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 140 insertions, 0 deletions

diff --git a/drivers/cxl/pmem.c b/drivers/cxl/pmem.c
new file mode 100644
index 000000000000..8365839856dc
--- /dev/null
+++ b/drivers/cxl/pmem.c
@@ -0,0 +1,140 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright(c) 2021 Intel Corporation. All rights reserved. */
+#include <linux/libnvdimm.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include "cxl.h"
+
+/*
+ * Ordered workqueue for cxl nvdimm device arrival and departure
+ * to coordinate bus rescans when a bridge arrives and trigger remove
+ * operations when the bridge is removed.
+ */
+static struct workqueue_struct *cxl_pmem_wq;
+
+static int cxl_pmem_ctl(struct nvdimm_bus_descriptor *nd_desc,
+			struct nvdimm *nvdimm, unsigned int cmd, void *buf,
+			unsigned int buf_len, int *cmd_rc)
+{
+	return -ENOTTY;
+}
+
+static bool online_nvdimm_bus(struct cxl_nvdimm_bridge *cxl_nvb)
+{
+	if (cxl_nvb->nvdimm_bus)
+		return true;
+	cxl_nvb->nvdimm_bus =
+		nvdimm_bus_register(&cxl_nvb->dev, &cxl_nvb->nd_desc);
+	return cxl_nvb->nvdimm_bus != NULL;
+}
+
+static void offline_nvdimm_bus(struct cxl_nvdimm_bridge *cxl_nvb)
+{
+	if (!cxl_nvb->nvdimm_bus)
+		return;
+	nvdimm_bus_unregister(cxl_nvb->nvdimm_bus);
+	cxl_nvb->nvdimm_bus = NULL;
+}
+
+static void cxl_nvb_update_state(struct work_struct *work)
+{
+	struct cxl_nvdimm_bridge *cxl_nvb =
+		container_of(work, typeof(*cxl_nvb), state_work);
+	bool release = false;
+
+	device_lock(&cxl_nvb->dev);
+	switch (cxl_nvb->state) {
+	case CXL_NVB_ONLINE:
+		if (!online_nvdimm_bus(cxl_nvb)) {
+			dev_err(&cxl_nvb->dev,
+				"failed to establish nvdimm bus\n");
+			release = true;
+		}
+		break;
+	case CXL_NVB_OFFLINE:
+	case CXL_NVB_DEAD:
+		offline_nvdimm_bus(cxl_nvb);
+		break;
+	default:
+		break;
+	}
+	device_unlock(&cxl_nvb->dev);
+
+	if (release)
+		device_release_driver(&cxl_nvb->dev);
+
+	put_device(&cxl_nvb->dev);
+}
+
+static void cxl_nvdimm_bridge_remove(struct device *dev)
+{
+	struct cxl_nvdimm_bridge *cxl_nvb = to_cxl_nvdimm_bridge(dev);
+
+	if (cxl_nvb->state == CXL_NVB_ONLINE)
+		cxl_nvb->state = CXL_NVB_OFFLINE;
+	if (queue_work(cxl_pmem_wq, &cxl_nvb->state_work))
+		get_device(&cxl_nvb->dev);
+}
+
+static int cxl_nvdimm_bridge_probe(struct device *dev)
+{
+	struct cxl_nvdimm_bridge *cxl_nvb = to_cxl_nvdimm_bridge(dev);
+
+	if (cxl_nvb->state == CXL_NVB_DEAD)
+		return -ENXIO;
+
+	if (cxl_nvb->state == CXL_NVB_NEW) {
+		cxl_nvb->nd_desc = (struct nvdimm_bus_descriptor) {
+			.provider_name = "CXL",
+			.module = THIS_MODULE,
+			.ndctl = cxl_pmem_ctl,
+		};
+
+		INIT_WORK(&cxl_nvb->state_work, cxl_nvb_update_state);
+	}
+
+	cxl_nvb->state = CXL_NVB_ONLINE;
+	if (queue_work(cxl_pmem_wq, &cxl_nvb->state_work))
+		get_device(&cxl_nvb->dev);
+
+	return 0;
+}
+
+static struct cxl_driver cxl_nvdimm_bridge_driver = {
+	.name = "cxl_nvdimm_bridge",
+	.probe = cxl_nvdimm_bridge_probe,
+	.remove = cxl_nvdimm_bridge_remove,
+	.id = CXL_DEVICE_NVDIMM_BRIDGE,
+};
+
+static __init int cxl_pmem_init(void)
+{
+	int rc;
+
+	cxl_pmem_wq = alloc_ordered_workqueue("cxl_pmem", 0);
+	if (!cxl_pmem_wq)
+		return -ENXIO;
+
+	rc = cxl_driver_register(&cxl_nvdimm_bridge_driver);
+	if (rc)
+		goto err;
+
+	return 0;
+
+err:
+	destroy_workqueue(cxl_pmem_wq);
+	return rc;
+}
+
+static __exit void cxl_pmem_exit(void)
+{
+	cxl_driver_unregister(&cxl_nvdimm_bridge_driver);
+	destroy_workqueue(cxl_pmem_wq);
+}
+
+MODULE_LICENSE("GPL v2");
+module_init(cxl_pmem_init);
+module_exit(cxl_pmem_exit);
+MODULE_IMPORT_NS(CXL);
+MODULE_ALIAS_CXL(CXL_DEVICE_NVDIMM_BRIDGE);