[PATCH RFC] fpga: add FPGA Bus device framework

[Wu Hao]

This patch is a RFC patch which replaces the patch[1] which
creates 'fpga-dev' class as container device. It introduces
a 'fpga' bus type, and provides interfaces to create/destroy
fpga bus devices. This fpga bus device only could be used as
a container device, and no drivers needed for it.

There is no interface change, so this patch could be used
together with other patches of the original patch set[2].

This following APIs are provided by FPGA Bus device framework:
* fpga_dev_create
  Create fpga bus device under the given parent device.
* fpga_dev_destroy
  Destroy fpga bus device

The following sysfs files are created:
* /sys/bus/fpga/devices/<fpga.x>/name
  Name of the fpga bus device.

[1] http://marc.info/?l=linux-fpga&m=149844237209829&w=2
[2] http://marc.info/?l=linux-fpga&m=149844232609819&w=2

Signed-off-by: Wu Hao <hao.wu@xxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-bus-fpga |   5 ++
 drivers/fpga/Kconfig                     |   6 ++
 drivers/fpga/Makefile                    |   3 +
 drivers/fpga/fpga-dev.c                  | 132 +++++++++++++++++++++++++++++++
 include/linux/fpga/fpga-dev.h            |  31 ++++++++
 5 files changed, 177 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-fpga
 create mode 100644 drivers/fpga/fpga-dev.c
 create mode 100644 include/linux/fpga/fpga-dev.h

diff --git a/Documentation/ABI/testing/sysfs-bus-fpga b/Documentation/ABI/testing/sysfs-bus-fpga
new file mode 100644
index 0000000..414e946
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-fpga
@@ -0,0 +1,5 @@
+What:		/sys/bus/fpga/devices/<fpga.x>/name
+Date:		August 2017
+KernelVersion:	4.13
+Contact:	Wu Hao <hao.wu@xxxxxxxxx>
+Description:	Name of FPGA bus device
diff --git a/drivers/fpga/Kconfig b/drivers/fpga/Kconfig
index d89eb52..b97a90e 100644
--- a/drivers/fpga/Kconfig
+++ b/drivers/fpga/Kconfig
@@ -12,6 +12,12 @@ config FPGA
 	  manager drivers.
 
 if FPGA
+config FPGA_DEVICE
+	tristate "FPGA Bus Device Framework"
+	help
+	  Say Y here if you want support for FPGA Bus devices from the
+	  kernel. The FPGA Bus Device Framework adds a FPGA Bus type and
+	  provide interfaces to create FPGA devices on the bus.
 
 config FPGA_REGION
 	tristate "FPGA Region"
diff --git a/drivers/fpga/Makefile b/drivers/fpga/Makefile
index 08fc728..3eb254e 100644
--- a/drivers/fpga/Makefile
+++ b/drivers/fpga/Makefile
@@ -5,6 +5,9 @@
 # Core FPGA Manager Framework
 obj-$(CONFIG_FPGA)			+= fpga-mgr.o
 
+# FPGA Bus Device Framework
+obj-$(CONFIG_FPGA_DEVICE)		+= fpga-dev.o
+
 # FPGA Manager Drivers
 obj-$(CONFIG_FPGA_MGR_ICE40_SPI)	+= ice40-spi.o
 obj-$(CONFIG_FPGA_MGR_SOCFPGA)		+= socfpga.o
diff --git a/drivers/fpga/fpga-dev.c b/drivers/fpga/fpga-dev.c
new file mode 100644
index 0000000..ddf67bb
--- /dev/null
+++ b/drivers/fpga/fpga-dev.c
@@ -0,0 +1,132 @@
+/*
+ * FPGA Bus Device Framework Driver
+ *
+ * Copyright (C) 2017 Intel Corporation, Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL version 2. See
+ * the COPYING file in the top-level directory.
+ */
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/fpga/fpga-dev.h>
+
+static DEFINE_IDA(fpga_dev_ida);
+static bool is_bus_registered;
+
+static void fpga_dev_release(struct device *dev)
+{
+	struct fpga_dev *fdev = to_fpga_dev(dev);
+
+	ida_simple_remove(&fpga_dev_ida, fdev->dev.id);
+	kfree(fdev);
+}
+
+static const struct device_type fpga_dev_type = {
+	.name		= "fpga_dev",
+	.release	= fpga_dev_release,
+};
+
+static ssize_t name_show(struct device *dev,
+			 struct device_attribute *attr, char *buf)
+{
+	struct fpga_dev *fdev = to_fpga_dev(dev);
+
+	return sprintf(buf, "%s\n", fdev->name);
+}
+static DEVICE_ATTR_RO(name);
+
+static struct attribute *fpga_dev_attrs[] = {
+	&dev_attr_name.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(fpga_dev);
+
+static struct bus_type fpga_bus_type = {
+	.name		= "fpga",
+};
+
+/**
+ * fpga_dev_create - create a fpga device on fpga bus
+ * @parent: parent device
+ * @name: fpga bus device name
+ *
+ * Return fpga_dev struct for success, error code otherwise.
+ */
+struct fpga_dev *fpga_dev_create(struct device *parent, const char *name)
+{
+	struct fpga_dev *fdev;
+	int id, ret = 0;
+
+	if (WARN_ON(!is_bus_registered))
+		return ERR_PTR(-ENODEV);
+
+	if (!name || !strlen(name)) {
+		dev_err(parent, "Attempt to register with no name!\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	fdev = kzalloc(sizeof(*fdev), GFP_KERNEL);
+	if (!fdev)
+		return ERR_PTR(-ENOMEM);
+
+	id = ida_simple_get(&fpga_dev_ida, 0, 0, GFP_KERNEL);
+	if (id < 0) {
+		ret = id;
+		goto error_kfree;
+	}
+
+	fdev->name = name;
+
+	device_initialize(&fdev->dev);
+	fdev->dev.type = &fpga_dev_type;
+	fdev->dev.bus = &fpga_bus_type;
+	fdev->dev.groups = fpga_dev_groups;
+	fdev->dev.parent = parent;
+	fdev->dev.id = id;
+
+	ret = dev_set_name(&fdev->dev, "fpga.%d", id);
+	if (ret)
+		goto error_device;
+
+	ret = device_add(&fdev->dev);
+	if (ret)
+		goto error_device;
+
+	dev_dbg(fdev->dev.parent, "fpga bus device [%s] created\n", fdev->name);
+
+	return fdev;
+
+error_device:
+	ida_simple_remove(&fpga_dev_ida, id);
+error_kfree:
+	kfree(fdev);
+
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(fpga_dev_create);
+
+static int __init fpga_bus_init(void)
+{
+	int ret;
+
+	pr_info("FPGA Bus Device Framework\n");
+
+	ret = bus_register(&fpga_bus_type);
+	if (ret)
+		return ret;
+
+	is_bus_registered = true;
+	return 0;
+}
+
+static void __exit fpga_bus_exit(void)
+{
+	bus_unregister(&fpga_bus_type);
+}
+
+MODULE_DESCRIPTION("FPGA Bus Device Framework");
+MODULE_LICENSE("GPL v2");
+
+subsys_initcall(fpga_bus_init);
+module_exit(fpga_bus_exit);
diff --git a/include/linux/fpga/fpga-dev.h b/include/linux/fpga/fpga-dev.h
new file mode 100644
index 0000000..7f6deb4
--- /dev/null
+++ b/include/linux/fpga/fpga-dev.h
@@ -0,0 +1,31 @@
+/*
+ * FPGA Bus Device Framework driver Header
+ *
+ * Copyright (C) 2017 Intel Corporation, Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL version 2. See
+ * the COPYING file in the top-level directory.
+ */
+#ifndef _LINUX_FPGA_DEV_H
+#define _LINUX_FPGA_DEV_H
+
+/**
+ * struct fpga_dev - fpga bus device structure
+ * @name: name of fpga bus device
+ * @dev: fpga bus device
+ */
+struct fpga_dev {
+	const char *name;
+	struct device dev;
+};
+
+#define to_fpga_dev(d) container_of(d, struct fpga_dev, dev)
+
+struct fpga_dev *fpga_dev_create(struct device *parent, const char *name);
+
+static inline void fpga_dev_destroy(struct fpga_dev *fdev)
+{
+	device_unregister(&fdev->dev);
+}
+
+#endif
-- 
1.8.3.1