[PATCH v2 2/5] cxl/pmem: Add initial infrastructure for pmem support

[Dan Williams]

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@xxxxxxxxxx>
Link: https://lore.kernel.org/r/162336396844.2462439.1234951573910835450.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 drivers/cxl/Kconfig  |   13 +++++
 drivers/cxl/Makefile |    2 +
 drivers/cxl/acpi.c   |   37 +++++++++++++
 drivers/cxl/core.c   |  121 +++++++++++++++++++++++++++++++++++++++++++
 drivers/cxl/cxl.h    |   24 +++++++++
 drivers/cxl/pmem.c   |  140 ++++++++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 335 insertions(+), 2 deletions(-)
 create mode 100644 drivers/cxl/pmem.c

diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index 1a44b173dcbc..e6de221cc568 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -61,5 +61,18 @@ config CXL_ACPI
 	  hierarchy to map regions that represent System RAM, or Persistent
 	  Memory regions to be managed by LIBNVDIMM.
 
+	  If unsure say 'm'.
+
+config CXL_PMEM
+	tristate "CXL PMEM: Persistent Memory Support"
+	depends on LIBNVDIMM
+	default CXL_BUS
+	help
+	  In addition to typical memory resources a platform may also advertise
+	  support for persistent memory attached via CXL. This support is
+	  managed via a bridge driver from CXL to the LIBNVDIMM system
+	  subsystem. Say 'y/m' to enable support for enumerating and
+	  provisioning the persistent memory capacity of CXL memory expanders.
+
 	  If unsure say 'm'.
 endif
diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
index a29efb3e8ad2..32954059b37b 100644
--- a/drivers/cxl/Makefile
+++ b/drivers/cxl/Makefile
@@ -2,8 +2,10 @@
 obj-$(CONFIG_CXL_BUS) += cxl_core.o
 obj-$(CONFIG_CXL_MEM) += cxl_pci.o
 obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
+obj-$(CONFIG_CXL_PMEM) += cxl_pmem.o
 
 ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=CXL
 cxl_core-y := core.o
 cxl_pci-y := pci.o
 cxl_acpi-y := acpi.o
+cxl_pmem-y := pmem.o
diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index be357eea552c..8a723f7f3f73 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -145,6 +145,30 @@ static int add_host_bridge_dport(struct device *match, void *arg)
 	return 0;
 }
 
+static int add_root_nvdimm_bridge(struct device *match, void *data)
+{
+	struct cxl_decoder *cxld;
+	struct cxl_port *root_port = data;
+	struct cxl_nvdimm_bridge *cxl_nvb;
+	struct device *host = root_port->dev.parent;
+
+	if (!is_root_decoder(match))
+		return 0;
+
+	cxld = to_cxl_decoder(match);
+	if (!(cxld->flags & CXL_DECODER_F_PMEM))
+		return 0;
+
+	cxl_nvb = devm_cxl_add_nvdimm_bridge(host, root_port);
+	if (IS_ERR(cxl_nvb)) {
+		dev_dbg(host, "failed to register pmem\n");
+		return PTR_ERR(cxl_nvb);
+	}
+	dev_dbg(host, "%s: add: %s\n", dev_name(&root_port->dev),
+		dev_name(&cxl_nvb->dev));
+	return 1;
+}
+
 static int cxl_acpi_probe(struct platform_device *pdev)
 {
 	int rc;
@@ -166,8 +190,17 @@ static int cxl_acpi_probe(struct platform_device *pdev)
 	 * Root level scanned with host-bridge as dports, now scan host-bridges
 	 * for their role as CXL uports to their CXL-capable PCIe Root Ports.
 	 */
-	return bus_for_each_dev(adev->dev.bus, NULL, root_port,
-				add_host_bridge_uport);
+	rc = bus_for_each_dev(adev->dev.bus, NULL, root_port,
+			      add_host_bridge_uport);
+	if (rc)
+		return rc;
+
+	if (IS_ENABLED(CONFIG_CXL_PMEM))
+		rc = device_for_each_child(&root_port->dev, root_port,
+					   add_root_nvdimm_bridge);
+	if (rc < 0)
+		return rc;
+	return 0;
 }
 
 static const struct acpi_device_id cxl_acpi_ids[] = {
diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
index 68d6afea363b..aaffb390d168 100644
--- a/drivers/cxl/core.c
+++ b/drivers/cxl/core.c
@@ -187,6 +187,12 @@ static const struct device_type cxl_decoder_root_type = {
 	.groups = cxl_decoder_root_attribute_groups,
 };
 
+bool is_root_decoder(struct device *dev)
+{
+	return dev->type == &cxl_decoder_root_type;
+}
+EXPORT_SYMBOL_GPL(is_root_decoder);
+
 struct cxl_decoder *to_cxl_decoder(struct device *dev)
 {
 	if (dev_WARN_ONCE(dev, dev->type->release != cxl_decoder_release,
@@ -194,6 +200,7 @@ struct cxl_decoder *to_cxl_decoder(struct device *dev)
 		return NULL;
 	return container_of(dev, struct cxl_decoder, dev);
 }
+EXPORT_SYMBOL_GPL(to_cxl_decoder);
 
 static void cxl_dport_release(struct cxl_dport *dport)
 {
@@ -611,6 +618,118 @@ void cxl_probe_component_regs(struct device *dev, void __iomem *base,
 }
 EXPORT_SYMBOL_GPL(cxl_probe_component_regs);
 
+static void cxl_nvdimm_bridge_release(struct device *dev)
+{
+	struct cxl_nvdimm_bridge *cxl_nvb = to_cxl_nvdimm_bridge(dev);
+
+	kfree(cxl_nvb);
+}
+
+static const struct attribute_group *cxl_nvdimm_bridge_attribute_groups[] = {
+	&cxl_base_attribute_group,
+	NULL,
+};
+
+static const struct device_type cxl_nvdimm_bridge_type = {
+	.name = "cxl_nvdimm_bridge",
+	.release = cxl_nvdimm_bridge_release,
+	.groups = cxl_nvdimm_bridge_attribute_groups,
+};
+
+struct cxl_nvdimm_bridge *to_cxl_nvdimm_bridge(struct device *dev)
+{
+	if (dev_WARN_ONCE(dev, dev->type != &cxl_nvdimm_bridge_type,
+			  "not a cxl_nvdimm_bridge device\n"))
+		return NULL;
+	return container_of(dev, struct cxl_nvdimm_bridge, dev);
+}
+EXPORT_SYMBOL_GPL(to_cxl_nvdimm_bridge);
+
+static struct cxl_nvdimm_bridge *
+cxl_nvdimm_bridge_alloc(struct cxl_port *port)
+{
+	struct cxl_nvdimm_bridge *cxl_nvb;
+	struct device *dev;
+
+	cxl_nvb = kzalloc(sizeof(*cxl_nvb), GFP_KERNEL);
+	if (!cxl_nvb)
+		return ERR_PTR(-ENOMEM);
+
+	dev = &cxl_nvb->dev;
+	cxl_nvb->port = port;
+	cxl_nvb->state = CXL_NVB_NEW;
+	device_initialize(dev);
+	device_set_pm_not_required(dev);
+	dev->parent = &port->dev;
+	dev->bus = &cxl_bus_type;
+	dev->type = &cxl_nvdimm_bridge_type;
+
+	return cxl_nvb;
+}
+
+static void unregister_nvb(void *_cxl_nvb)
+{
+	struct cxl_nvdimm_bridge *cxl_nvb = _cxl_nvb;
+	bool flush;
+
+	/*
+	 * If the bridge was ever activated then there might be in-flight state
+	 * work to flush. Once the state has been changed to 'dead' then no new
+	 * work can be queued by user-triggered bind.
+	 */
+	device_lock(&cxl_nvb->dev);
+	flush = cxl_nvb->state != CXL_NVB_NEW;
+	cxl_nvb->state = CXL_NVB_DEAD;
+	device_unlock(&cxl_nvb->dev);
+
+	/*
+	 * Even though the device core will trigger device_release_driver()
+	 * before the unregister, it does not know about the fact that
+	 * cxl_nvdimm_bridge_driver defers ->remove() work. So, do the driver
+	 * release not and flush it before tearing down the nvdimm device
+	 * hierarchy.
+	 */
+	device_release_driver(&cxl_nvb->dev);
+	if (flush)
+		flush_work(&cxl_nvb->state_work);
+	device_unregister(&cxl_nvb->dev);
+}
+
+struct cxl_nvdimm_bridge *devm_cxl_add_nvdimm_bridge(struct device *host,
+						     struct cxl_port *port)
+{
+	struct cxl_nvdimm_bridge *cxl_nvb;
+	struct device *dev;
+	int rc;
+
+	if (!IS_ENABLED(CONFIG_CXL_PMEM))
+		return ERR_PTR(-ENXIO);
+
+	cxl_nvb = cxl_nvdimm_bridge_alloc(port);
+	if (IS_ERR(cxl_nvb))
+		return cxl_nvb;
+
+	dev = &cxl_nvb->dev;
+	rc = dev_set_name(dev, "nvdimm-bridge");
+	if (rc)
+		goto err;
+
+	rc = device_add(dev);
+	if (rc)
+		goto err;
+
+	rc = devm_add_action_or_reset(host, unregister_nvb, cxl_nvb);
+	if (rc)
+		return ERR_PTR(rc);
+
+	return cxl_nvb;
+
+err:
+	put_device(dev);
+	return ERR_PTR(rc);
+}
+EXPORT_SYMBOL_GPL(devm_cxl_add_nvdimm_bridge);
+
 /**
  * cxl_probe_device_regs() - Detect CXL Device register blocks
  * @dev: Host device of the @base mapping
@@ -808,6 +927,8 @@ EXPORT_SYMBOL_GPL(cxl_driver_unregister);
 
 static int cxl_device_id(struct device *dev)
 {
+	if (dev->type == &cxl_nvdimm_bridge_type)
+		return CXL_DEVICE_NVDIMM_BRIDGE;
 	return 0;
 }
 
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index a6f8e7097ea2..5da2163ca45f 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -4,6 +4,7 @@
 #ifndef __CXL_H__
 #define __CXL_H__
 
+#include <linux/libnvdimm.h>
 #include <linux/bitfield.h>
 #include <linux/bitops.h>
 #include <linux/io.h>
@@ -202,6 +203,23 @@ struct cxl_decoder {
 	struct cxl_dport *target[];
 };
 
+
+enum cxl_nvdimm_brige_state {
+	CXL_NVB_NEW,
+	CXL_NVB_DEAD,
+	CXL_NVB_ONLINE,
+	CXL_NVB_OFFLINE,
+};
+
+struct cxl_nvdimm_bridge {
+	struct device dev;
+	struct cxl_port *port;
+	struct nvdimm_bus *nvdimm_bus;
+	struct nvdimm_bus_descriptor nd_desc;
+	struct work_struct state_work;
+	enum cxl_nvdimm_brige_state state;
+};
+
 /**
  * struct cxl_port - logical collection of upstream port devices and
  *		     downstream port devices to construct a CXL memory
@@ -247,6 +265,7 @@ int cxl_add_dport(struct cxl_port *port, struct device *dport, int port_id,
 		  resource_size_t component_reg_phys);
 
 struct cxl_decoder *to_cxl_decoder(struct device *dev);
+bool is_root_decoder(struct device *dev);
 struct cxl_decoder *
 devm_cxl_add_decoder(struct device *host, struct cxl_port *port, int nr_targets,
 		     resource_size_t base, resource_size_t len,
@@ -287,7 +306,12 @@ int __cxl_driver_register(struct cxl_driver *cxl_drv, struct module *owner,
 #define cxl_driver_register(x) __cxl_driver_register(x, THIS_MODULE, KBUILD_MODNAME)
 void cxl_driver_unregister(struct cxl_driver *cxl_drv);
 
+#define CXL_DEVICE_NVDIMM_BRIDGE 1
+
 #define MODULE_ALIAS_CXL(type) MODULE_ALIAS("cxl:t" __stringify(type) "*")
 #define CXL_MODALIAS_FMT "cxl:t%d"
 
+struct cxl_nvdimm_bridge *to_cxl_nvdimm_bridge(struct device *dev);
+struct cxl_nvdimm_bridge *devm_cxl_add_nvdimm_bridge(struct device *host,
+						     struct cxl_port *port);
 #endif /* __CXL_H__ */
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);