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authorLinus Torvalds <torvalds@linux-foundation.org>2014-06-12 23:27:40 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-12 23:27:40 +0200
commitf9da455b93f6ba076935b4ef4589f61e529ae046 (patch)
tree3c4e69ce1ba1d6bf65915b97a76ca2172105b278 /Documentation/networking/cdc_mbim.txt
parentMerge tag 'dm-3.16-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/... (diff)
parentrtnetlink: fix userspace API breakage for iproute2 < v3.9.0 (diff)
downloadlinux-f9da455b93f6ba076935b4ef4589f61e529ae046.tar.xz
linux-f9da455b93f6ba076935b4ef4589f61e529ae046.zip
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
Pull networking updates from David Miller: 1) Seccomp BPF filters can now be JIT'd, from Alexei Starovoitov. 2) Multiqueue support in xen-netback and xen-netfront, from Andrew J Benniston. 3) Allow tweaking of aggregation settings in cdc_ncm driver, from Bjørn Mork. 4) BPF now has a "random" opcode, from Chema Gonzalez. 5) Add more BPF documentation and improve test framework, from Daniel Borkmann. 6) Support TCP fastopen over ipv6, from Daniel Lee. 7) Add software TSO helper functions and use them to support software TSO in mvneta and mv643xx_eth drivers. From Ezequiel Garcia. 8) Support software TSO in fec driver too, from Nimrod Andy. 9) Add Broadcom SYSTEMPORT driver, from Florian Fainelli. 10) Handle broadcasts more gracefully over macvlan when there are large numbers of interfaces configured, from Herbert Xu. 11) Allow more control over fwmark used for non-socket based responses, from Lorenzo Colitti. 12) Do TCP congestion window limiting based upon measurements, from Neal Cardwell. 13) Support busy polling in SCTP, from Neal Horman. 14) Allow RSS key to be configured via ethtool, from Venkata Duvvuru. 15) Bridge promisc mode handling improvements from Vlad Yasevich. 16) Don't use inetpeer entries to implement ID generation any more, it performs poorly, from Eric Dumazet. * git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next: (1522 commits) rtnetlink: fix userspace API breakage for iproute2 < v3.9.0 tcp: fixing TLP's FIN recovery net: fec: Add software TSO support net: fec: Add Scatter/gather support net: fec: Increase buffer descriptor entry number net: fec: Factorize feature setting net: fec: Enable IP header hardware checksum net: fec: Factorize the .xmit transmit function bridge: fix compile error when compiling without IPv6 support bridge: fix smatch warning / potential null pointer dereference via-rhine: fix full-duplex with autoneg disable bnx2x: Enlarge the dorq threshold for VFs bnx2x: Check for UNDI in uncommon branch bnx2x: Fix 1G-baseT link bnx2x: Fix link for KR with swapped polarity lane sctp: Fix sk_ack_backlog wrap-around problem net/core: Add VF link state control policy net/fsl: xgmac_mdio is dependent on OF_MDIO net/fsl: Make xgmac_mdio read error message useful net_sched: drr: warn when qdisc is not work conserving ...
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+ 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 an 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 managament 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 an 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] "/proc/bus/usb filesystem output"
+ - Documentation/usb/proc_usb_info.txt
+
+[7] "/sys/bus/usb/devices/.../descriptors"
+ - Documentation/ABI/stable/sysfs-bus-usb