[PATCH v2 02/22] fpga: add FPGA device framework

[Wu Hao]

During FPGA device (e.g PCI-based) discovery, platform devices are
registered for different FPGA function units. But the device node path
isn't quite friendly to applications.

Consider this case, applications want to access child device's sysfs file
for some information.

1) Access using bus-based path (e.g PCI)

  /sys/bus/pci/devices/xxxxx/fpga_func_a.0/sysfs_file

  From the path, it's clear which PCI device is the parent, but not perfect
  solution for applications. PCI device BDF is not fixed, application may
  need to search all PCI device to find the actual FPGA Device.

2) Or access using platform device path

  /sys/bus/platform/devices/fpga_func_a.0/sysfs_file

  Applications find the actual function by name easily, but no information
  about which fpga device it belongs to. It's quite confusing if multiple
  FPGA devices are in one system.

'FPGA Device' class is introduced to resolve this problem. Each node under
this class represents a fpga device, which may have one or more child
devices. Applications only need to search under this FPGA Device class
folder to find the child device node it needs.

For example, for the platform has 2 fpga devices, each fpga device has
3 child devices, the hierarchy looks like this.

Two nodes are under /sys/class/fpga/:
/sys/class/fpga/fpga.0
/sys/class/fpga/fpga.1

Each node has 1 function A device and 2 function B devices:
/sys/class/fpga/fpga.0/func_a.0
/sys/class/fpga/fpga.0/func_b.0
/sys/class/fpga/fpga.0/func_b.1

/sys/class/fpga/fpga.1/func_a.1
/sys/class/fpga/fpga.1/func_b.2
/sys/class/fpga/fpga.1/func_b.3

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

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

Signed-off-by: Tim Whisonant <tim.whisonant@xxxxxxxxx>
Signed-off-by: Enno Luebbers <enno.luebbers@xxxxxxxxx>
Signed-off-by: Shiva Rao <shiva.rao@xxxxxxxxx>
Signed-off-by: Christopher Rauer <christopher.rauer@xxxxxxxxx>
Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
Signed-off-by: Wu Hao <hao.wu@xxxxxxxxx>
---
v2: added sysfs documentation for fpga-dev class.
    switched to GPLv2 license.
---
 Documentation/ABI/testing/sysfs-class-fpga-dev |   5 ++
 drivers/fpga/Kconfig                           |   6 ++
 drivers/fpga/Makefile                          |   3 +
 drivers/fpga/fpga-dev.c                        | 118 +++++++++++++++++++++++++
 include/linux/fpga/fpga-dev.h                  |  31 +++++++
 5 files changed, 163 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-class-fpga-dev
 create mode 100644 drivers/fpga/fpga-dev.c
 create mode 100644 include/linux/fpga/fpga-dev.h

diff --git a/Documentation/ABI/testing/sysfs-class-fpga-dev b/Documentation/ABI/testing/sysfs-class-fpga-dev
new file mode 100644
index 0000000..ce162df
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-fpga-dev
@@ -0,0 +1,5 @@
+What:		/sys/class/fpga/<device>/name
+Date:		June 2017
+KernelVersion:	4.12
+Contact:	Wu Hao <hao.wu@xxxxxxxxx>
+Description:	Name of FPGA device
diff --git a/drivers/fpga/Kconfig b/drivers/fpga/Kconfig
index 394c141..ed600d5 100644
--- a/drivers/fpga/Kconfig
+++ b/drivers/fpga/Kconfig
@@ -12,6 +12,12 @@ config FPGA
 	  manager drivers.
 
 if FPGA
+config FPGA_DEVICE
+	tristate "FPGA Device Framework"
+	help
+	  Say Y here if you want support for FPGA Devices from the kernel.
+	  The FPGA Device Framework adds a FPGA device class and provide
+	  interfaces to create FPGA devices.
 
 config FPGA_REGION
 	tristate "FPGA Region"
diff --git a/drivers/fpga/Makefile b/drivers/fpga/Makefile
index 85b45d0..8950a8f 100644
--- a/drivers/fpga/Makefile
+++ b/drivers/fpga/Makefile
@@ -5,6 +5,9 @@
 # Core FPGA Manager Framework
 obj-$(CONFIG_FPGA)			+= fpga-mgr.o
 
+# FPGA 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..5778ebc
--- /dev/null
+++ b/drivers/fpga/fpga-dev.c
@@ -0,0 +1,118 @@
+/*
+ * FPGA 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 struct class *fpga_dev_class;
+
+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);
+
+/**
+ * fpga_dev_create - create a fpga device
+ * @parent: parent device
+ * @name: fpga 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 (!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.class = fpga_dev_class;
+	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 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 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 int __init fpga_dev_class_init(void)
+{
+	pr_info("FPGA Device framework\n");
+
+	fpga_dev_class = class_create(THIS_MODULE, "fpga");
+	if (IS_ERR(fpga_dev_class))
+		return PTR_ERR(fpga_dev_class);
+
+	fpga_dev_class->dev_groups = fpga_dev_groups;
+	fpga_dev_class->dev_release = fpga_dev_release;
+
+	return 0;
+}
+
+static void __exit fpga_dev_class_exit(void)
+{
+	class_destroy(fpga_dev_class);
+}
+
+MODULE_DESCRIPTION("FPGA Device framework");
+MODULE_LICENSE("GPL v2");
+
+subsys_initcall(fpga_dev_class_init);
+module_exit(fpga_dev_class_exit);
diff --git a/include/linux/fpga/fpga-dev.h b/include/linux/fpga/fpga-dev.h
new file mode 100644
index 0000000..ee693cc
--- /dev/null
+++ b/include/linux/fpga/fpga-dev.h
@@ -0,0 +1,31 @@
+/*
+ * FPGA Device 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 device structure
+ * @name: name of fpga device
+ * @dev: fpga 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