[linux-block.git] / Documentation / networking / cdc_mbim.rst

.. SPDX-License-Identifier: GPL-2.0

======================================================
cdc_mbim - Driver for CDC MBIM Mobile Broadband modems
======================================================

The cdc_mbim driver supports USB devices conforming to the "Universal
Serial Bus Communications Class Subclass Specification for Mobile
Broadband Interface Model" [1], which is a further development of
"Universal Serial Bus Communications Class Subclass Specifications for
Network Control Model Devices" [2] optimized for Mobile Broadband
devices, aka "3G/LTE modems".


Command Line Parameters
=======================

The cdc_mbim driver has no parameters of its own.  But the probing
behaviour for NCM 1.0 backwards compatible MBIM functions (an
"NCM/MBIM function" as defined in section 3.2 of [1]) is affected
by a cdc_ncm driver parameter:

prefer_mbim
-----------
:Type:          Boolean
:Valid Range:   N/Y (0-1)
:Default Value: Y (MBIM is preferred)

This parameter sets the system policy for NCM/MBIM functions.  Such
functions will be handled by either the cdc_ncm driver or the cdc_mbim
driver depending on the prefer_mbim setting.  Setting prefer_mbim=N
makes the cdc_mbim driver ignore these functions and lets the cdc_ncm
driver handle them instead.

The parameter is writable, and can be changed at any time. A manual
unbind/bind is required to make the change effective for NCM/MBIM
functions bound to the "wrong" driver


Basic usage
===========

MBIM functions are inactive when unmanaged. The cdc_mbim driver only
provides a userspace interface to the MBIM control channel, and will
not participate in the management of the function. This implies that a
userspace MBIM management application always is required to enable a
MBIM function.

Such userspace applications includes, but are not limited to:

 - mbimcli (included with the libmbim [3] library), and
 - ModemManager [4]

Establishing a MBIM IP session reequires at least these actions by the
management application:

 - open the control channel
 - configure network connection settings
 - connect to network
 - configure IP interface

Management application development
----------------------------------
The driver <-> userspace interfaces are described below.  The MBIM
control channel protocol is described in [1].


MBIM control channel userspace ABI
==================================

/dev/cdc-wdmX character device
------------------------------
The driver creates a two-way pipe to the MBIM function control channel
using the cdc-wdm driver as a subdriver.  The userspace end of the
control channel pipe is a /dev/cdc-wdmX character device.

The cdc_mbim driver does not process or police messages on the control
channel.  The channel is fully delegated to the userspace management
application.  It is therefore up to this application to ensure that it
complies with all the control channel requirements in [1].

The cdc-wdmX device is created as a child of the MBIM control
interface USB device.  The character device associated with a specific
MBIM function can be looked up using sysfs.  For example::

 bjorn@nemi:~$ ls /sys/bus/usb/drivers/cdc_mbim/2-4:2.12/usbmisc
 cdc-wdm0

 bjorn@nemi:~$ grep . /sys/bus/usb/drivers/cdc_mbim/2-4:2.12/usbmisc/cdc-wdm0/dev
 180:0


USB configuration descriptors
-----------------------------
The wMaxControlMessage field of the CDC MBIM functional descriptor
limits the maximum control message size. The management application is
responsible for negotiating a control message size complying with the
requirements in section 9.3.1 of [1], taking this descriptor field
into consideration.

The userspace application can access the CDC MBIM functional
descriptor of a MBIM function using either of the two USB
configuration descriptor kernel interfaces described in [6] or [7].

See also the ioctl documentation below.


Fragmentation
-------------
The userspace application is responsible for all control message
fragmentation and defragmentaion, as described in section 9.5 of [1].


/dev/cdc-wdmX write()
---------------------
The MBIM control messages from the management application *must not*
exceed the negotiated control message size.


/dev/cdc-wdmX read()
--------------------
The management application *must* accept control messages of up the
negotiated control message size.


/dev/cdc-wdmX ioctl()
---------------------
IOCTL_WDM_MAX_COMMAND: Get Maximum Command Size
This ioctl returns the wMaxControlMessage field of the CDC MBIM
functional descriptor for MBIM devices.  This is intended as a
convenience, eliminating the need to parse the USB descriptors from
userspace.

::

	#include <stdio.h>
	#include <fcntl.h>
	#include <sys/ioctl.h>
	#include <linux/types.h>
	#include <linux/usb/cdc-wdm.h>
	int main()
	{
		__u16 max;
		int fd = open("/dev/cdc-wdm0", O_RDWR);
		if (!ioctl(fd, IOCTL_WDM_MAX_COMMAND, &max))
			printf("wMaxControlMessage is %d\n", max);
	}


Custom device services
----------------------
The MBIM specification allows vendors to freely define additional
services.  This is fully supported by the cdc_mbim driver.

Support for new MBIM services, including vendor specified services, is
implemented entirely in userspace, like the rest of the MBIM control
protocol

New services should be registered in the MBIM Registry [5].


MBIM data channel userspace ABI
===============================

wwanY network device
--------------------
The cdc_mbim driver represents the MBIM data channel as a single
network device of the "wwan" type. This network device is initially
mapped to MBIM IP session 0.


Multiplexed IP sessions (IPS)
-----------------------------
MBIM allows multiplexing up to 256 IP sessions over a single USB data
channel.  The cdc_mbim driver models such IP sessions as 802.1q VLAN
subdevices of the master wwanY device, mapping MBIM IP session Z to
VLAN ID Z for all values of Z greater than 0.

The device maximum Z is given in the MBIM_DEVICE_CAPS_INFO structure
described in section 10.5.1 of [1].

The userspace management application is responsible for adding new
VLAN links prior to establishing MBIM IP sessions where the SessionId
is greater than 0. These links can be added by using the normal VLAN
kernel interfaces, either ioctl or netlink.

For example, adding a link for a MBIM IP session with SessionId 3::

  ip link add link wwan0 name wwan0.3 type vlan id 3

The driver will automatically map the "wwan0.3" network device to MBIM
IP session 3.


Device Service Streams (DSS)
----------------------------
MBIM also allows up to 256 non-IP data streams to be multiplexed over
the same shared USB data channel.  The cdc_mbim driver models these
sessions as another set of 802.1q VLAN subdevices of the master wwanY
device, mapping MBIM DSS session A to VLAN ID (256 + A) for all values
of A.

The device maximum A is given in the MBIM_DEVICE_SERVICES_INFO
structure described in section 10.5.29 of [1].

The DSS VLAN subdevices are used as a practical interface between the
shared MBIM data channel and a MBIM DSS aware userspace application.
It is not intended to be presented as-is to an end user. The
assumption is that a userspace application initiating a DSS session
also takes care of the necessary framing of the DSS data, presenting
the stream to the end user in an appropriate way for the stream type.

The network device ABI requires a dummy ethernet header for every DSS
data frame being transported.  The contents of this header is
arbitrary, with the following exceptions:

 - TX frames using an IP protocol (0x0800 or 0x86dd) will be dropped
 - RX frames will have the protocol field set to ETH_P_802_3 (but will
   not be properly formatted 802.3 frames)
 - RX frames will have the destination address set to the hardware
   address of the master device

The DSS supporting userspace management application is responsible for
adding the dummy ethernet header on TX and stripping it on RX.

This is a simple example using tools commonly available, exporting
DssSessionId 5 as a pty character device pointed to by a /dev/nmea
symlink::

  ip link add link wwan0 name wwan0.dss5 type vlan id 261
  ip link set dev wwan0.dss5 up
  socat INTERFACE:wwan0.dss5,type=2 PTY:,echo=0,link=/dev/nmea

This is only an example, most suitable for testing out a DSS
service. Userspace applications supporting specific MBIM DSS services
are expected to use the tools and programming interfaces required by
that service.

Note that adding VLAN links for DSS sessions is entirely optional.  A
management application may instead choose to bind a packet socket
directly to the master network device, using the received VLAN tags to
map frames to the correct DSS session and adding 18 byte VLAN ethernet
headers with the appropriate tag on TX.  In this case using a socket
filter is recommended, matching only the DSS VLAN subset. This avoid
unnecessary copying of unrelated IP session data to userspace.  For
example::

  static struct sock_filter dssfilter[] = {
	/* use special negative offsets to get VLAN tag */
	BPF_STMT(BPF_LD|BPF_B|BPF_ABS, SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT),
	BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, 1, 0, 6), /* true */

	/* verify DSS VLAN range */
	BPF_STMT(BPF_LD|BPF_H|BPF_ABS, SKF_AD_OFF + SKF_AD_VLAN_TAG),
	BPF_JUMP(BPF_JMP|BPF_JGE|BPF_K, 256, 0, 4),	/* 256 is first DSS VLAN */
	BPF_JUMP(BPF_JMP|BPF_JGE|BPF_K, 512, 3, 0),	/* 511 is last DSS VLAN */

	/* verify ethertype */
	BPF_STMT(BPF_LD|BPF_H|BPF_ABS, 2 * ETH_ALEN),
	BPF_JUMP(BPF_JMP|BPF_JEQ|BPF_K, ETH_P_802_3, 0, 1),

	BPF_STMT(BPF_RET|BPF_K, (u_int)-1),	/* accept */
	BPF_STMT(BPF_RET|BPF_K, 0),		/* ignore */
  };


Tagged IP session 0 VLAN
------------------------
As described above, MBIM IP session 0 is treated as special by the
driver.  It is initially mapped to untagged frames on the wwanY
network device.

This mapping implies a few restrictions on multiplexed IPS and DSS
sessions, which may not always be practical:

 - no IPS or DSS session can use a frame size greater than the MTU on
   IP session 0
 - no IPS or DSS session can be in the up state unless the network
   device representing IP session 0 also is up

These problems can be avoided by optionally making the driver map IP
session 0 to a VLAN subdevice, similar to all other IP sessions.  This
behaviour is triggered by adding a VLAN link for the magic VLAN ID
4094.  The driver will then immediately start mapping MBIM IP session
0 to this VLAN, and will drop untagged frames on the master wwanY
device.

Tip: It might be less confusing to the end user to name this VLAN
subdevice after the MBIM SessionID instead of the VLAN ID.  For
example::

  ip link add link wwan0 name wwan0.0 type vlan id 4094


VLAN mapping
------------

Summarizing the cdc_mbim driver mapping described above, we have this
relationship between VLAN tags on the wwanY network device and MBIM
sessions on the shared USB data channel::

  VLAN ID       MBIM type   MBIM SessionID           Notes
  ---------------------------------------------------------
  untagged      IPS         0                        a)
  1 - 255       IPS         1 - 255 <VLANID>
  256 - 511     DSS         0 - 255 <VLANID - 256>
  512 - 4093                                         b)
  4094          IPS         0                        c)

    a) if no VLAN ID 4094 link exists, else dropped
    b) unsupported VLAN range, unconditionally dropped
    c) if a VLAN ID 4094 link exists, else dropped


References
==========

 1) USB Implementers Forum, Inc. - "Universal Serial Bus
    Communications Class Subclass Specification for Mobile Broadband
    Interface Model", Revision 1.0 (Errata 1), May 1, 2013

      - http://www.usb.org/developers/docs/devclass_docs/

 2) USB Implementers Forum, Inc. - "Universal Serial Bus
    Communications Class Subclass Specifications for Network Control
    Model Devices", Revision 1.0 (Errata 1), November 24, 2010

      - http://www.usb.org/developers/docs/devclass_docs/

 3) libmbim - "a glib-based library for talking to WWAN modems and
    devices which speak the Mobile Interface Broadband Model (MBIM)
    protocol"

      - http://www.freedesktop.org/wiki/Software/libmbim/

 4) ModemManager - "a DBus-activated daemon which controls mobile
    broadband (2G/3G/4G) devices and connections"

      - http://www.freedesktop.org/wiki/Software/ModemManager/

 5) "MBIM (Mobile Broadband Interface Model) Registry"

       - http://compliance.usb.org/mbim/

 6) "/sys/kernel/debug/usb/devices output format"

       - Documentation/driver-api/usb/usb.rst

 7) "/sys/bus/usb/devices/.../descriptors"

       - Documentation/ABI/stable/sysfs-bus-usb
Commit	Line	Data
92f06f42 MCC	1	.. SPDX-License-Identifier: GPL-2.0
	2
	3	======================================================
	4	cdc_mbim - Driver for CDC MBIM Mobile Broadband modems
	5	======================================================
a563babe BM	6
	7	The cdc_mbim driver supports USB devices conforming to the "Universal
	8	Serial Bus Communications Class Subclass Specification for Mobile
	9	Broadband Interface Model" [1], which is a further development of
	10	"Universal Serial Bus Communications Class Subclass Specifications for
	11	Network Control Model Devices" [2] optimized for Mobile Broadband
	12	devices, aka "3G/LTE modems".
	13
	14
	15	Command Line Parameters
	16	=======================
	17
	18	The cdc_mbim driver has no parameters of its own. But the probing
	19	behaviour for NCM 1.0 backwards compatible MBIM functions (an
	20	"NCM/MBIM function" as defined in section 3.2 of [1]) is affected
	21	by a cdc_ncm driver parameter:
	22
	23	prefer_mbim
	24	-----------
92f06f42 MCC	25	:Type: Boolean
	26	:Valid Range: N/Y (0-1)
	27	:Default Value: Y (MBIM is preferred)
a563babe BM	28
	29	This parameter sets the system policy for NCM/MBIM functions. Such
	30	functions will be handled by either the cdc_ncm driver or the cdc_mbim
	31	driver depending on the prefer_mbim setting. Setting prefer_mbim=N
	32	makes the cdc_mbim driver ignore these functions and lets the cdc_ncm
	33	driver handle them instead.
	34
	35	The parameter is writable, and can be changed at any time. A manual
	36	unbind/bind is required to make the change effective for NCM/MBIM
	37	functions bound to the "wrong" driver
	38
	39
	40	Basic usage
	41	===========
	42
	43	MBIM functions are inactive when unmanaged. The cdc_mbim driver only
9332ef9d	44	provides a userspace interface to the MBIM control channel, and will
a563babe BM	45	not participate in the management of the function. This implies that a
	46	userspace MBIM management application always is required to enable a
	47	MBIM function.
	48
	49	Such userspace applications includes, but are not limited to:
92f06f42	50
a563babe BM	51	- mbimcli (included with the libmbim [3] library), and
	52	- ModemManager [4]
	53
	54	Establishing a MBIM IP session reequires at least these actions by the
	55	management application:
92f06f42	56
a563babe BM	57	- open the control channel
	58	- configure network connection settings
	59	- connect to network
	60	- configure IP interface
	61
	62	Management application development
	63	----------------------------------
	64	The driver <-> userspace interfaces are described below. The MBIM
	65	control channel protocol is described in [1].
	66
	67
	68	MBIM control channel userspace ABI
	69	==================================
	70
	71	/dev/cdc-wdmX character device
	72	------------------------------
	73	The driver creates a two-way pipe to the MBIM function control channel
	74	using the cdc-wdm driver as a subdriver. The userspace end of the
	75	control channel pipe is a /dev/cdc-wdmX character device.
	76
	77	The cdc_mbim driver does not process or police messages on the control
	78	channel. The channel is fully delegated to the userspace management
	79	application. It is therefore up to this application to ensure that it
	80	complies with all the control channel requirements in [1].
	81
	82	The cdc-wdmX device is created as a child of the MBIM control
	83	interface USB device. The character device associated with a specific
92f06f42	84	MBIM function can be looked up using sysfs. For example::
a563babe BM	85
	86	bjorn@nemi:~$ ls /sys/bus/usb/drivers/cdc_mbim/2-4:2.12/usbmisc
	87	cdc-wdm0
	88
	89	bjorn@nemi:~$ grep . /sys/bus/usb/drivers/cdc_mbim/2-4:2.12/usbmisc/cdc-wdm0/dev
	90	180:0
	91
	92
	93	USB configuration descriptors
	94	-----------------------------
	95	The wMaxControlMessage field of the CDC MBIM functional descriptor
a266ef69	96	limits the maximum control message size. The management application is
a563babe BM	97	responsible for negotiating a control message size complying with the
	98	requirements in section 9.3.1 of [1], taking this descriptor field
	99	into consideration.
	100
	101	The userspace application can access the CDC MBIM functional
	102	descriptor of a MBIM function using either of the two USB
	103	configuration descriptor kernel interfaces described in [6] or [7].
	104
	105	See also the ioctl documentation below.
	106
	107
	108	Fragmentation
	109	-------------
	110	The userspace application is responsible for all control message
	111	fragmentation and defragmentaion, as described in section 9.5 of [1].
	112
	113
	114	/dev/cdc-wdmX write()
	115	---------------------
	116	The MBIM control messages from the management application must not
	117	exceed the negotiated control message size.
	118
	119
	120	/dev/cdc-wdmX read()
	121	--------------------
	122	The management application must accept control messages of up the
	123	negotiated control message size.
	124
	125
	126	/dev/cdc-wdmX ioctl()
92f06f42	127	---------------------
a563babe BM	128	IOCTL_WDM_MAX_COMMAND: Get Maximum Command Size
	129	This ioctl returns the wMaxControlMessage field of the CDC MBIM
	130	functional descriptor for MBIM devices. This is intended as a
	131	convenience, eliminating the need to parse the USB descriptors from
	132	userspace.
	133
92f06f42 MCC	134	::
92f06f42 MCC	135
a563babe BM	136	#include <stdio.h>
	137	#include <fcntl.h>
	138	#include <sys/ioctl.h>
	139	#include <linux/types.h>
	140	#include <linux/usb/cdc-wdm.h>
	141	int main()
	142	{
	143	__u16 max;
	144	int fd = open("/dev/cdc-wdm0", O_RDWR);
	145	if (!ioctl(fd, IOCTL_WDM_MAX_COMMAND, &max))
	146	printf("wMaxControlMessage is %d\n", max);
	147	}
	148
	149
	150	Custom device services
	151	----------------------
	152	The MBIM specification allows vendors to freely define additional
	153	services. This is fully supported by the cdc_mbim driver.
	154
	155	Support for new MBIM services, including vendor specified services, is
	156	implemented entirely in userspace, like the rest of the MBIM control
	157	protocol
	158
	159	New services should be registered in the MBIM Registry [5].
	160
	161
	162
	163	MBIM data channel userspace ABI
	164	===============================
	165
	166	wwanY network device
	167	--------------------
	168	The cdc_mbim driver represents the MBIM data channel as a single
	169	network device of the "wwan" type. This network device is initially
	170	mapped to MBIM IP session 0.
	171
	172
	173	Multiplexed IP sessions (IPS)
	174	-----------------------------
	175	MBIM allows multiplexing up to 256 IP sessions over a single USB data
	176	channel. The cdc_mbim driver models such IP sessions as 802.1q VLAN
	177	subdevices of the master wwanY device, mapping MBIM IP session Z to
	178	VLAN ID Z for all values of Z greater than 0.
	179
	180	The device maximum Z is given in the MBIM_DEVICE_CAPS_INFO structure
	181	described in section 10.5.1 of [1].
	182
	183	The userspace management application is responsible for adding new
	184	VLAN links prior to establishing MBIM IP sessions where the SessionId
	185	is greater than 0. These links can be added by using the normal VLAN
	186	kernel interfaces, either ioctl or netlink.
	187
92f06f42	188	For example, adding a link for a MBIM IP session with SessionId 3::
a563babe BM	189
	190	ip link add link wwan0 name wwan0.3 type vlan id 3
	191
	192	The driver will automatically map the "wwan0.3" network device to MBIM
	193	IP session 3.
	194
	195
	196	Device Service Streams (DSS)
	197	----------------------------
	198	MBIM also allows up to 256 non-IP data streams to be multiplexed over
	199	the same shared USB data channel. The cdc_mbim driver models these
	200	sessions as another set of 802.1q VLAN subdevices of the master wwanY
	201	device, mapping MBIM DSS session A to VLAN ID (256 + A) for all values
	202	of A.
	203
	204	The device maximum A is given in the MBIM_DEVICE_SERVICES_INFO
	205	structure described in section 10.5.29 of [1].
	206
	207	The DSS VLAN subdevices are used as a practical interface between the
	208	shared MBIM data channel and a MBIM DSS aware userspace application.
	209	It is not intended to be presented as-is to an end user. The
9332ef9d	210	assumption is that a userspace application initiating a DSS session
a563babe BM	211	also takes care of the necessary framing of the DSS data, presenting
	212	the stream to the end user in an appropriate way for the stream type.
	213
	214	The network device ABI requires a dummy ethernet header for every DSS
	215	data frame being transported. The contents of this header is
	216	arbitrary, with the following exceptions:
92f06f42	217
a563babe BM	218	- TX frames using an IP protocol (0x0800 or 0x86dd) will be dropped
	219	- RX frames will have the protocol field set to ETH_P_802_3 (but will
	220	not be properly formatted 802.3 frames)
	221	- RX frames will have the destination address set to the hardware
	222	address of the master device
	223
	224	The DSS supporting userspace management application is responsible for
	225	adding the dummy ethernet header on TX and stripping it on RX.
	226
	227	This is a simple example using tools commonly available, exporting
	228	DssSessionId 5 as a pty character device pointed to by a /dev/nmea
92f06f42	229	symlink::
a563babe BM	230
	231	ip link add link wwan0 name wwan0.dss5 type vlan id 261
	232	ip link set dev wwan0.dss5 up
	233	socat INTERFACE:wwan0.dss5,type=2 PTY:,echo=0,link=/dev/nmea
	234
	235	This is only an example, most suitable for testing out a DSS
	236	service. Userspace applications supporting specific MBIM DSS services
	237	are expected to use the tools and programming interfaces required by
	238	that service.
	239
	240	Note that adding VLAN links for DSS sessions is entirely optional. A
	241	management application may instead choose to bind a packet socket
	242	directly to the master network device, using the received VLAN tags to
	243	map frames to the correct DSS session and adding 18 byte VLAN ethernet
	244	headers with the appropriate tag on TX. In this case using a socket
	245	filter is recommended, matching only the DSS VLAN subset. This avoid
	246	unnecessary copying of unrelated IP session data to userspace. For
92f06f42	247	example::
a563babe BM	248
	249	static struct sock_filter dssfilter[] = {
	250	/* use special negative offsets to get VLAN tag */
	251	BPF_STMT(BPF_LD\|BPF_B\|BPF_ABS, SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT),
	252	BPF_JUMP(BPF_JMP\|BPF_JEQ\|BPF_K, 1, 0, 6), /* true */
	253
	254	/* verify DSS VLAN range */
	255	BPF_STMT(BPF_LD\|BPF_H\|BPF_ABS, SKF_AD_OFF + SKF_AD_VLAN_TAG),
	256	BPF_JUMP(BPF_JMP\|BPF_JGE\|BPF_K, 256, 0, 4), /* 256 is first DSS VLAN */
	257	BPF_JUMP(BPF_JMP\|BPF_JGE\|BPF_K, 512, 3, 0), /* 511 is last DSS VLAN */
	258
	259	/* verify ethertype */
92f06f42 MCC	260	BPF_STMT(BPF_LD\|BPF_H\|BPF_ABS, 2 * ETH_ALEN),
92f06f42 MCC	261	BPF_JUMP(BPF_JMP\|BPF_JEQ\|BPF_K, ETH_P_802_3, 0, 1),
a563babe	262
92f06f42 MCC	263	BPF_STMT(BPF_RET\|BPF_K, (u_int)-1), /* accept */
92f06f42 MCC	264	BPF_STMT(BPF_RET\|BPF_K, 0), /* ignore */
a563babe BM	265	};
	266
	267
	268
	269	Tagged IP session 0 VLAN
	270	------------------------
	271	As described above, MBIM IP session 0 is treated as special by the
	272	driver. It is initially mapped to untagged frames on the wwanY
	273	network device.
	274
	275	This mapping implies a few restrictions on multiplexed IPS and DSS
	276	sessions, which may not always be practical:
92f06f42	277
a563babe BM	278	- no IPS or DSS session can use a frame size greater than the MTU on
	279	IP session 0
	280	- no IPS or DSS session can be in the up state unless the network
	281	device representing IP session 0 also is up
	282
	283	These problems can be avoided by optionally making the driver map IP
	284	session 0 to a VLAN subdevice, similar to all other IP sessions. This
	285	behaviour is triggered by adding a VLAN link for the magic VLAN ID
	286	4094. The driver will then immediately start mapping MBIM IP session
	287	0 to this VLAN, and will drop untagged frames on the master wwanY
	288	device.
	289
	290	Tip: It might be less confusing to the end user to name this VLAN
	291	subdevice after the MBIM SessionID instead of the VLAN ID. For
92f06f42	292	example::
a563babe BM	293
	294	ip link add link wwan0 name wwan0.0 type vlan id 4094
	295
	296
	297	VLAN mapping
	298	------------
	299
	300	Summarizing the cdc_mbim driver mapping described above, we have this
	301	relationship between VLAN tags on the wwanY network device and MBIM
92f06f42	302	sessions on the shared USB data channel::
a563babe BM	303
	304	VLAN ID MBIM type MBIM SessionID Notes
	305	---------------------------------------------------------
	306	untagged IPS 0 a)
	307	1 - 255 IPS 1 - 255 <VLANID>
	308	256 - 511 DSS 0 - 255 <VLANID - 256>
	309	512 - 4093 b)
	310	4094 IPS 0 c)
	311
	312	a) if no VLAN ID 4094 link exists, else dropped
	313	b) unsupported VLAN range, unconditionally dropped
	314	c) if a VLAN ID 4094 link exists, else dropped
	315
	316
	317
	318
	319	References
	320	==========
	321
92f06f42 MCC	322	1) USB Implementers Forum, Inc. - "Universal Serial Bus
	323	Communications Class Subclass Specification for Mobile Broadband
	324	Interface Model", Revision 1.0 (Errata 1), May 1, 2013
	325
a563babe BM	326	- http://www.usb.org/developers/docs/devclass_docs/
a563babe BM	327
92f06f42 MCC	328	2) USB Implementers Forum, Inc. - "Universal Serial Bus
	329	Communications Class Subclass Specifications for Network Control
	330	Model Devices", Revision 1.0 (Errata 1), November 24, 2010
	331
a563babe BM	332	- http://www.usb.org/developers/docs/devclass_docs/
a563babe BM	333
92f06f42 MCC	334	3) libmbim - "a glib-based library for talking to WWAN modems and
	335	devices which speak the Mobile Interface Broadband Model (MBIM)
	336	protocol"
	337
a563babe BM	338	- http://www.freedesktop.org/wiki/Software/libmbim/
a563babe BM	339
92f06f42 MCC	340	4) ModemManager - "a DBus-activated daemon which controls mobile
	341	broadband (2G/3G/4G) devices and connections"
	342
a563babe BM	343	- http://www.freedesktop.org/wiki/Software/ModemManager/
a563babe BM	344
92f06f42 MCC	345	5) "MBIM (Mobile Broadband Interface Model) Registry"
92f06f42 MCC	346
a563babe BM	347	- http://compliance.usb.org/mbim/
a563babe BM	348
92f06f42 MCC	349	6) "/sys/kernel/debug/usb/devices output format"
92f06f42 MCC	350
4269a691	351	- Documentation/driver-api/usb/usb.rst
a563babe	352
92f06f42 MCC	353	7) "/sys/bus/usb/devices/.../descriptors"
92f06f42 MCC	354
a563babe	355	- Documentation/ABI/stable/sysfs-bus-usb