usb: gadget: add RNDIS configfs option for Windows rndiscmp.inf compatibility

This adds a new configfs attribute named `use_ms_rndiscmp`. It is a
boolean value that is used to select the class/subclass/protocol used
by the RNDIS function interface association descriptor. By default,
this is 0x02 (Comm), 0x06 (Ethernet), 0xff (None). When the
use_ms_rndiscmp attribute is set to true, the values 0xef (Misc),
0x04 (RNDIS), 0x01 (Ethernet) will be used instead. This class/subclass/
protocol combination is recognized by the rndiscmp.inf file in Windows
Vista and newer and will cause Windows to load the correct RNDIS driver
without the need for a custom (signed) .inf file.

Signed-off-by: David Lechner <david@lechnology.com>

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

@@ -16,4 +16,7 @@ Description:
 		class		USB interface class, default is 02 (hex)
 		subclass	USB interface subclass, default is 06 (hex)
 		protocol	USB interface protocol, default is 00 (hex)
+		use_ms_rndiscmp	Use the MS Windows rndiscmp.inf compatible
+				class 0xEF, subclass 0x04, protocol 0x01
+				instead of the default 0x02/0x06/0x00.
 		=========	=============================================

drivers/usb/gadget/function/f_rndis.c

@@ -16,6 +16,7 @@
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/etherdevice.h>
+#include <linux/usb/misc.h>
 
 #include <linux/atomic.h>
 
@@ -681,6 +682,18 @@ rndis_bind(struct usb_configuration *c, struct usb_function *f)
 	rndis_iad_descriptor.bFunctionSubClass = rndis_opts->subclass;
 	rndis_iad_descriptor.bFunctionProtocol = rndis_opts->protocol;
 
+	/*
+	 * Starting with Vista, Windows will match this Class/SubClass/Protocol
+	 * with rndiscmp.inf and load the proper driver without the need for a
+	 * custom .inf.
+	 * Ref: https://msdn.microsoft.com/library/ff538820(v=vs.85).aspx
+	 */
+	if (rndis_opts->use_ms_rndiscmp) {
+		rndis_iad_descriptor.bFunctionClass = USB_CLASS_MISC;
+		rndis_iad_descriptor.bFunctionSubClass = USB_MISC_SUBCLASS_RNDIS;
+		rndis_iad_descriptor.bFunctionProtocol = USB_MISC_RNDIS_PROTO_ENET;
+	}
+
 	/*
 	 * in drivers/usb/gadget/configfs.c:configfs_composite_bind()
 	 * configurations are bound in sequence with list_for_each_entry,
@@ -863,6 +876,40 @@ USB_ETHER_CONFIGFS_ITEM_ATTR_U8_RW(rndis, subclass);
 /* f_rndis_opts_protocol */
 USB_ETHER_CONFIGFS_ITEM_ATTR_U8_RW(rndis, protocol);
 
+static ssize_t
+rndis_opts_use_ms_rndiscmp_show(struct config_item *item, char *page)
+{
+	struct f_rndis_opts *opts = to_f_rndis_opts(item);
+	int ret;
+
+	mutex_lock(&opts->lock);
+	ret = sprintf(page, "%d\n", opts->use_ms_rndiscmp);
+	mutex_unlock(&opts->lock);
+
+	return ret;
+}
+
+static ssize_t
+rndis_opts_use_ms_rndiscmp_store(struct config_item *item, const char *page,
+				 size_t len)
+{
+	struct f_rndis_opts *opts = to_f_rndis_opts(item);
+	int ret;
+	bool use;
+
+	mutex_lock(&opts->lock);
+	ret = strtobool(page, &use);
+	if (!ret) {
+		opts->use_ms_rndiscmp = use;
+		ret = len;
+	}
+	mutex_unlock(&opts->lock);
+
+	return ret;
+}
+
+CONFIGFS_ATTR(rndis_opts_, use_ms_rndiscmp);
+
 static struct configfs_attribute *rndis_attrs[] = {
 	&rndis_opts_attr_dev_addr,
 	&rndis_opts_attr_host_addr,
@@ -871,6 +918,7 @@ static struct configfs_attribute *rndis_attrs[] = {
 	&rndis_opts_attr_class,
 	&rndis_opts_attr_subclass,
 	&rndis_opts_attr_protocol,
+	&rndis_opts_attr_use_ms_rndiscmp,
 	NULL,
 };
 

drivers/usb/gadget/function/u_rndis.h

@@ -22,6 +22,7 @@ struct f_rndis_opts {
 	struct net_device		*net;
 	bool				bound;
 	bool				borrowed_net;
+	bool				use_ms_rndiscmp;
 
 	struct config_group		*rndis_interf_group;
 	struct usb_os_desc		rndis_os_desc;

include/uapi/linux/usb/misc.h

@@ -0,0 +1,14 @@
+/*
+ * USB Miscellaneous Device Class definitions
+ *
+ * Ref: http://www.usb.org/developers/defined_class/#BaseClassEFh
+ */
+
+#ifndef __UAPI_LINUX_USB_MISC_H
+#define __UAPI_LINUX_USB_MISC_H
+
+#define USB_MISC_SUBCLASS_RNDIS			0x04
+
+#define USB_MISC_RNDIS_PROTO_ENET		0x01
+
+#endif /* __UAPI_LINUX_USB_MISC_H */