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

[David Lechner <david@lechnology.com>]

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>
---
 .../ABI/testing/configfs-usb-gadget-rndis          |  3 ++
 drivers/usb/gadget/function/f_rndis.c              | 48 ++++++++++++++++++++++
 drivers/usb/gadget/function/u_rndis.h              |  1 +
 include/uapi/linux/usb/misc.h                      | 14 +++++++
 4 files changed, 66 insertions(+)
 create mode 100644 include/uapi/linux/usb/misc.h

diff --git a/Documentation/ABI/testing/configfs-usb-gadget-rndis b/Documentation/ABI/testing/configfs-usb-gadget-rndis
index e32879b..bb4b5a85 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-rndis
+++ b/Documentation/ABI/testing/configfs-usb-gadget-rndis
@@ -12,3 +12,6 @@ Description:
 				Ethernet over USB link
 		dev_addr	- MAC address of device's end of this
 				Ethernet over USB link
+		use_ms_rndiscmp	- Use the MS Windows rndiscmp.inf compatible
+				class 0xEF, subclass 0x04, protocol 0x01
+				instead of the default 0x02/0x06/0x00.
diff --git a/drivers/usb/gadget/function/f_rndis.c b/drivers/usb/gadget/function/f_rndis.c
index 16562e4..b92f4f4 100644
--- a/drivers/usb/gadget/function/f_rndis.c
+++ b/drivers/usb/gadget/function/f_rndis.c
@@ -20,6 +20,7 @@
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/etherdevice.h>
+#include <linux/usb/misc.h>
 
 #include <linux/atomic.h>
 
@@ -692,6 +693,18 @@ rndis_bind(struct usb_configuration *c, struct usb_function *f)
 	}
 
 	/*
+	 * 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,
 	 * in each configuration its functions are bound in sequence
@@ -866,11 +879,46 @@ USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(rndis);
 /* f_rndis_opts_ifname */
 USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(rndis);
 
+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,
 	&rndis_opts_attr_qmult,
 	&rndis_opts_attr_ifname,
+	&rndis_opts_attr_use_ms_rndiscmp,
 	NULL,
 };
 
diff --git a/drivers/usb/gadget/function/u_rndis.h b/drivers/usb/gadget/function/u_rndis.h
index 4eafd50..03f241f 100644
--- a/drivers/usb/gadget/function/u_rndis.h
+++ b/drivers/usb/gadget/function/u_rndis.h
@@ -25,6 +25,7 @@ struct f_rndis_opts {
 	struct net_device		*net;
 	bool				bound;
 	bool				borrowed_net;
+	bool				use_ms_rndiscmp;
 
 	struct usb_os_desc		rndis_os_desc;
 	char				rndis_ext_compat_id[16];
diff --git a/include/uapi/linux/usb/misc.h b/include/uapi/linux/usb/misc.h
new file mode 100644
index 0000000..a6661f6
--- /dev/null
+++ b/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 */
-- 
2.7.4