usb: gadget: f_ncm: Add OS descriptor support

To be able to use the default USB class drivers available in Microsoft
Windows, we need to add OS descriptors to the exported USB gadget to
tell the OS that we are compatible with the built-in drivers.

Copy the OS descriptor support from f_rndis into f_ncm. As a result,
using the WINNCM compatible ID, the UsbNcm driver is loaded on
enumeration without the need for a custom driver or inf file.
Signed-off-by: Romain Izard <romain.izard.pro@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/function/f_ncm.c

@@ -23,6 +23,7 @@
 #include "u_ether.h"
 #include "u_ether_configfs.h"
 #include "u_ncm.h"
+#include "configfs.h"
 
 /*
  * This function is a "CDC Network Control Model" (CDC NCM) Ethernet link.
@@ -1391,6 +1392,16 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 		return -EINVAL;
 
 	ncm_opts = container_of(f->fi, struct f_ncm_opts, func_inst);
+
+	if (cdev->use_os_string) {
+		f->os_desc_table = kzalloc(sizeof(*f->os_desc_table),
+					   GFP_KERNEL);
+		if (!f->os_desc_table)
+			return -ENOMEM;
+		f->os_desc_n = 1;
+		f->os_desc_table[0].os_desc = &ncm_opts->ncm_os_desc;
+	}
+
 	/*
 	 * in drivers/usb/gadget/configfs.c:configfs_composite_bind()
 	 * configurations are bound in sequence with list_for_each_entry,
@@ -1404,13 +1415,15 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 		status = gether_register_netdev(ncm_opts->net);
 		mutex_unlock(&ncm_opts->lock);
 		if (status)
-			return status;
+			goto fail;
 		ncm_opts->bound = true;
 	}
 	us = usb_gstrings_attach(cdev, ncm_strings,
 				 ARRAY_SIZE(ncm_string_defs));
-	if (IS_ERR(us))
-		return PTR_ERR(us);
+	if (IS_ERR(us)) {
+		status = PTR_ERR(us);
+		goto fail;
+	}
 	ncm_control_intf.iInterface = us[STRING_CTRL_IDX].id;
 	ncm_data_nop_intf.iInterface = us[STRING_DATA_IDX].id;
 	ncm_data_intf.iInterface = us[STRING_DATA_IDX].id;
@@ -1427,6 +1440,10 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 	ncm_control_intf.bInterfaceNumber = status;
 	ncm_union_desc.bMasterInterface0 = status;
 
+	if (cdev->use_os_string)
+		f->os_desc_table[0].if_id =
+			ncm_iad_desc.bFirstInterface;
+
 	status = usb_interface_id(c, f);
 	if (status < 0)
 		goto fail;
@@ -1506,6 +1523,9 @@ static int ncm_bind(struct usb_configuration *c, struct usb_function *f)
 	return 0;
 
 fail:
+	kfree(f->os_desc_table);
+	f->os_desc_n = 0;
+
 	if (ncm->notify_req) {
 		kfree(ncm->notify_req->buf);
 		usb_ep_free_request(ncm->notify, ncm->notify_req);
@@ -1560,16 +1580,22 @@ static void ncm_free_inst(struct usb_function_instance *f)
 		gether_cleanup(netdev_priv(opts->net));
 	else
 		free_netdev(opts->net);
+	kfree(opts->ncm_interf_group);
 	kfree(opts);
 }
 
 static struct usb_function_instance *ncm_alloc_inst(void)
 {
 	struct f_ncm_opts *opts;
+	struct usb_os_desc *descs[1];
+	char *names[1];
+	struct config_group *ncm_interf_group;
 
 	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
 	if (!opts)
 		return ERR_PTR(-ENOMEM);
+	opts->ncm_os_desc.ext_compat_id = opts->ncm_ext_compat_id;
+
 	mutex_init(&opts->lock);
 	opts->func_inst.free_func_inst = ncm_free_inst;
 	opts->net = gether_setup_default();
@@ -1578,8 +1604,20 @@ static struct usb_function_instance *ncm_alloc_inst(void)
 		kfree(opts);
 		return ERR_CAST(net);
 	}
+	INIT_LIST_HEAD(&opts->ncm_os_desc.ext_prop);
+
+	descs[0] = &opts->ncm_os_desc;
+	names[0] = "ncm";
 
 	config_group_init_type_name(&opts->func_inst.group, "", &ncm_func_type);
+	ncm_interf_group =
+		usb_os_desc_prepare_interf_dir(&opts->func_inst.group, 1, descs,
+					       names, THIS_MODULE);
+	if (IS_ERR(ncm_interf_group)) {
+		ncm_free_inst(&opts->func_inst);
+		return ERR_CAST(ncm_interf_group);
+	}
+	opts->ncm_interf_group = ncm_interf_group;
 
 	return &opts->func_inst;
 }
@@ -1605,6 +1643,9 @@ static void ncm_unbind(struct usb_configuration *c, struct usb_function *f)
 
 	hrtimer_cancel(&ncm->task_timer);
 
+	kfree(f->os_desc_table);
+	f->os_desc_n = 0;
+
 	ncm_string_defs[0].id = 0;
 	usb_free_all_descriptors(f);
 

drivers/usb/gadget/function/u_ncm.h

@@ -20,6 +20,9 @@ struct f_ncm_opts {
 	struct net_device		*net;
 	bool				bound;
 
+	struct config_group		*ncm_interf_group;
+	struct usb_os_desc		ncm_os_desc;
+	char				ncm_ext_compat_id[16];
 	/*
 	 * Read/write access to configfs attributes is handled by configfs.
 	 *