iio: core: Introduce IIO configfs support

This patch creates the IIO configfs root group. The group
will appear under <mount-point>/iio/, usually /config/iio.

We introduce configfs support in IIO in order to be able to easily
create IIO objects from userspace. The first supported IIO objects
are triggers introduced with next patches.

Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
Tested-by: Matt Ranostay <matt.ranostay@intel>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/Kconfig

@@ -22,6 +22,14 @@ if IIO_BUFFER
 	source "drivers/iio/buffer/Kconfig"
 endif # IIO_BUFFER
 
+config IIO_CONFIGFS
+	tristate "Enable IIO configuration via configfs"
+	select CONFIGFS_FS
+	help
+	  This allows configuring various IIO bits through configfs
+	  (e.g. software triggers). For more info see
+	  Documentation/iio/iio_configfs.txt.
+
 config IIO_TRIGGER
 	bool "Enable triggered sampling support"
 	help

drivers/iio/Makefile

@@ -7,6 +7,7 @@ industrialio-y := industrialio-core.o industrialio-event.o inkern.o
 industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
 industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
 
+obj-$(CONFIG_IIO_CONFIGFS) += industrialio-configfs.o
 obj-$(CONFIG_IIO_TRIGGERED_EVENT) += industrialio-triggered-event.o
 
 obj-y += accel/

drivers/iio/industrialio-configfs.c

@@ -0,0 +1,50 @@
+/*
+ * Industrial I/O configfs bits
+ *
+ * Copyright (c) 2015 Intel Corporation
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ */
+
+#include <linux/configfs.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kmod.h>
+#include <linux/slab.h>
+
+#include <linux/iio/iio.h>
+
+static struct config_item_type iio_root_group_type = {
+	.ct_owner       = THIS_MODULE,
+};
+
+struct configfs_subsystem iio_configfs_subsys = {
+	.su_group = {
+		.cg_item = {
+			.ci_namebuf = "iio",
+			.ci_type = &iio_root_group_type,
+		},
+	},
+	.su_mutex = __MUTEX_INITIALIZER(iio_configfs_subsys.su_mutex),
+};
+EXPORT_SYMBOL(iio_configfs_subsys);
+
+static int __init iio_configfs_init(void)
+{
+	config_group_init(&iio_configfs_subsys.su_group);
+
+	return configfs_register_subsystem(&iio_configfs_subsys);
+}
+module_init(iio_configfs_init);
+
+static void __exit iio_configfs_exit(void)
+{
+	configfs_unregister_subsystem(&iio_configfs_subsys);
+}
+module_exit(iio_configfs_exit);
+
+MODULE_AUTHOR("Daniel Baluta <daniel.baluta@intel.com>");
+MODULE_DESCRIPTION("Industrial I/O configfs support");
+MODULE_LICENSE("GPL v2");