NTB: switchtec_ntb: Introduce initial NTB driver

Seeing the Switchtec NTB hardware shares the same endpoint as the
management endpoint we utilize the class_interface API to register
an NTB driver for every Switchtec device in the system that has the
NTB class code.

Signed-off-by: Logan Gunthorpe <[e-mail]>
Reviewed-by: Stephen Bates <[e-mail]>
Reviewed-by: Kurt Schwemmer <[e-mail]>
Acked-by: Allen Hubbe <[e-mail]>
Acked-by: Bjorn Helgaas <[e-mail]>
Signed-off-by: Jon Mason <[e-mail]>

MAINTAINERS

···
 F:	drivers/pci/switch/switchtec*
 F:	include/uapi/linux/switchtec_ioctl.h
 F:	include/linux/switchtec.h
+F:	drivers/ntb/hw/mscc/
 
 PCI DRIVER FOR MVEBU (Marvell Armada 370 and Armada XP SOC support)
 M:	Thomas Petazzoni <[e-mail]>

drivers/ntb/hw/Kconfig

···
 source "drivers/ntb/hw/amd/Kconfig"
 source "drivers/ntb/hw/idt/Kconfig"
 source "drivers/ntb/hw/intel/Kconfig"
+source "drivers/ntb/hw/mscc/Kconfig"

drivers/ntb/hw/Makefile

···
 obj-$(CONFIG_NTB_AMD)	+= amd/
 obj-$(CONFIG_NTB_IDT)	+= idt/
 obj-$(CONFIG_NTB_INTEL)	+= intel/
+obj-$(CONFIG_NTB_SWITCHTEC) += mscc/

drivers/ntb/hw/mscc/Kconfig

···
+config NTB_SWITCHTEC
+	tristate "MicroSemi Switchtec Non-Transparent Bridge Support"
+	select PCI_SW_SWITCHTEC
+	help
+	 Enables NTB support for Switchtec PCI switches. This also
+	 selects the Switchtec management driver as they share the same
+	 hardware interface.
+
+	 If unsure, say N.

drivers/ntb/hw/mscc/Makefile

···
+obj-$(CONFIG_NTB_SWITCHTEC) += ntb_hw_switchtec.o

drivers/ntb/hw/mscc/ntb_hw_switchtec.c

···
+/*
+ * Microsemi Switchtec(tm) PCIe Management Driver
+ * Copyright (c) 2017, Microsemi Corporation
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ */
+
+#include <linux/switchtec.h>
+#include <linux/module.h>
+
+MODULE_DESCRIPTION("Microsemi Switchtec(tm) NTB Driver");
+MODULE_VERSION("0.1");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Microsemi Corporation");
+
+struct switchtec_ntb {
+	struct switchtec_dev *stdev;
+};
+
+static int switchtec_ntb_add(struct device *dev,
+			     struct class_interface *class_intf)
+{
+	struct switchtec_dev *stdev = to_stdev(dev);
+	struct switchtec_ntb *sndev;
+
+	stdev->sndev = NULL;
+
+	if (stdev->pdev->class != MICROSEMI_NTB_CLASSCODE)
+		return -ENODEV;
+
+	sndev = kzalloc_node(sizeof(*sndev), GFP_KERNEL, dev_to_node(dev));
+	if (!sndev)
+		return -ENOMEM;
+
+	sndev->stdev = stdev;
+
+	stdev->sndev = sndev;
+	dev_info(dev, "NTB device registered");
+
+	return 0;
+}
+
+void switchtec_ntb_remove(struct device *dev,
+			  struct class_interface *class_intf)
+{
+	struct switchtec_dev *stdev = to_stdev(dev);
+	struct switchtec_ntb *sndev = stdev->sndev;
+
+	if (!sndev)
+		return;
+
+	stdev->sndev = NULL;
+	kfree(sndev);
+	dev_info(dev, "ntb device unregistered");
+}
+
+static struct class_interface switchtec_interface  = {
+	.add_dev = switchtec_ntb_add,
+	.remove_dev = switchtec_ntb_remove,
+};
+
+static int __init switchtec_ntb_init(void)
+{
+	switchtec_interface.class = switchtec_class;
+	return class_interface_register(&switchtec_interface);
+}
+module_init(switchtec_ntb_init);
+
+static void __exit switchtec_ntb_exit(void)
+{
+	class_interface_unregister(&switchtec_interface);
+}
+module_exit(switchtec_ntb_exit);

drivers/pci/switch/switchtec.c

···
 	struct switchtec_dev *stdev;
 	int rc;
 
+	if (pdev->class == MICROSEMI_NTB_CLASSCODE)
+		request_module_nowait("ntb_hw_switchtec");
+
 	stdev = stdev_create(pdev);
 	if (IS_ERR(stdev))
 		return PTR_ERR(stdev);

include/linux/switchtec.h

···
 	u32 reserved4[174];
 } __packed;
 
+struct switchtec_ntb;
+
 struct switchtec_dev {
 	struct pci_dev *pdev;
 	struct device dev;
···
 	struct work_struct link_event_work;
 	void (*link_notifier)(struct switchtec_dev *stdev);
 	u8 link_event_count[SWITCHTEC_MAX_PFF_CSR];
+
+	struct switchtec_ntb *sndev;
 };
 
 static inline struct switchtec_dev *to_stdev(struct device *dev)