usb: gadget: f_eem: add configfs support

f_eem learns about our configfs interface so we
can remove in-kernel gadget drivers in future.
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

Documentation/ABI/testing/configfs-usb-gadget-eem

+What:		/config/usb-gadget/gadget/functions/eem.name
+Date:		May 2013
+KenelVersion:	3.11
+Description:
+		The attributes:
+
+		ifname		- network device interface name associated with
+				this function instance
+		qmult		- queue length multiplier for high and
+				super speed
+		host_addr	- MAC address of host's end of this
+				Ethernet over USB link
+		dev_addr	- MAC address of device's end of this
+				Ethernet over USB link

drivers/usb/gadget/Kconfig

@@ -544,6 +544,21 @@ choice
 
 # this first set of drivers all depend on bulk-capable hardware.
 
+config USB_CONFIGFS_EEM
+	bool "Ethernet Emulation Model (EEM)"
+	depends on USB_CONFIGFS
+	depends on NET
+	select USB_U_ETHER
+	select USB_F_EEM
+	help
+	  CDC EEM is a newer USB standard that is somewhat simpler than CDC ECM
+	  and therefore can be supported by more hardware.  Technically ECM and
+	  EEM are designed for different applications.  The ECM model extends
+	  the network interface to the target (e.g. a USB cable modem), and the
+	  EEM model is for mobile devices to communicate with hosts using
+	  ethernet over USB.  For Linux gadgets, however, the interface with
+	  the host is the same (a usbX device), so the differences are minimal.
+
 config USB_CONFIGFS_PHONET
 	boolean "Phonet protocol"
 	depends on USB_CONFIGFS

drivers/usb/gadget/f_eem.c

@@ -19,6 +19,7 @@
 #include <linux/slab.h>
 
 #include "u_ether.h"
+#include "u_ether_configfs.h"
 #include "u_eem.h"
 
 #define EEM_HLEN 2
@@ -263,8 +264,10 @@ static int eem_bind(struct usb_configuration *c, struct usb_function *f)
 	 * with regard to eem_opts->bound access
 	 */
 	if (!eem_opts->bound) {
+		mutex_lock(&eem_opts->lock);
 		gether_set_gadget(eem_opts->net, cdev->gadget);
 		status = gether_register_netdev(eem_opts->net);
+		mutex_unlock(&eem_opts->lock);
 		if (status)
 			return status;
 		eem_opts->bound = true;
@@ -533,6 +536,41 @@ static int eem_unwrap(struct gether *port,
 	return status;
 }
 
+static inline struct f_eem_opts *to_f_eem_opts(struct config_item *item)
+{
+	return container_of(to_config_group(item), struct f_eem_opts,
+			    func_inst.group);
+}
+
+/* f_eem_item_ops */
+USB_ETHERNET_CONFIGFS_ITEM(eem);
+
+/* f_eem_opts_dev_addr */
+USB_ETHERNET_CONFIGFS_ITEM_ATTR_DEV_ADDR(eem);
+
+/* f_eem_opts_host_addr */
+USB_ETHERNET_CONFIGFS_ITEM_ATTR_HOST_ADDR(eem);
+
+/* f_eem_opts_qmult */
+USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(eem);
+
+/* f_eem_opts_ifname */
+USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(eem);
+
+static struct configfs_attribute *eem_attrs[] = {
+	&f_eem_opts_dev_addr.attr,
+	&f_eem_opts_host_addr.attr,
+	&f_eem_opts_qmult.attr,
+	&f_eem_opts_ifname.attr,
+	NULL,
+};
+
+static struct config_item_type eem_func_type = {
+	.ct_item_ops	= &eem_item_ops,
+	.ct_attrs	= eem_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
 static void eem_free_inst(struct usb_function_instance *f)
 {
 	struct f_eem_opts *opts;
@@ -552,20 +590,28 @@ static struct usb_function_instance *eem_alloc_inst(void)
 	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
 	if (!opts)
 		return ERR_PTR(-ENOMEM);
+	mutex_init(&opts->lock);
 	opts->func_inst.free_func_inst = eem_free_inst;
 	opts->net = gether_setup_default();
 	if (IS_ERR(opts->net))
 		return ERR_CAST(opts->net);
 
+	config_group_init_type_name(&opts->func_inst.group, "", &eem_func_type);
+
 	return &opts->func_inst;
 }
 
 static void eem_free(struct usb_function *f)
 {
 	struct f_eem *eem;
+	struct f_eem_opts *opts;
 
 	eem = func_to_eem(f);
+	opts = container_of(f->fi, struct f_eem_opts, func_inst);
 	kfree(eem);
+	mutex_lock(&opts->lock);
+	opts->refcnt--;
+	mutex_unlock(&opts->lock);
 }
 
 static void eem_unbind(struct usb_configuration *c, struct usb_function *f)
@@ -586,8 +632,11 @@ struct usb_function *eem_alloc(struct usb_function_instance *fi)
 		return ERR_PTR(-ENOMEM);
 
 	opts = container_of(fi, struct f_eem_opts, func_inst);
+	mutex_lock(&opts->lock);
+	opts->refcnt++;
 
 	eem->port.ioport = netdev_priv(opts->net);
+	mutex_unlock(&opts->lock);
 	eem->port.cdc_filter = DEFAULT_FILTER;
 
 	eem->port.func.name = "cdc_eem";

drivers/usb/gadget/u_eem.h

@@ -22,6 +22,15 @@ struct f_eem_opts {
 	struct usb_function_instance	func_inst;
 	struct net_device		*net;
 	bool				bound;
+
+	/*
+	 * Read/write access to configfs attributes is handled by configfs.
+	 *
+	 * This is to protect the data from concurrent access by read/write
+	 * and create symlink/remove symlink.
+	 */
+	struct mutex			lock;
+	int				refcnt;
 };
 
 #endif /* U_EEM_H */