Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1437 insertions, 0 deletions

diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst
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+===================================
+SocketCAN - Controller Area Network
+===================================
+
+Overview / What is SocketCAN
+============================
+
+The socketcan package is an implementation of CAN protocols
+(Controller Area Network) for Linux.  CAN is a networking technology
+which has widespread use in automation, embedded devices, and
+automotive fields.  While there have been other CAN implementations
+for Linux based on character devices, SocketCAN uses the Berkeley
+socket API, the Linux network stack and implements the CAN device
+drivers as network interfaces.  The CAN socket API has been designed
+as similar as possible to the TCP/IP protocols to allow programmers,
+familiar with network programming, to easily learn how to use CAN
+sockets.
+
+
+.. _socketcan-motivation:
+
+Motivation / Why Using the Socket API
+=====================================
+
+There have been CAN implementations for Linux before SocketCAN so the
+question arises, why we have started another project.  Most existing
+implementations come as a device driver for some CAN hardware, they
+are based on character devices and provide comparatively little
+functionality.  Usually, there is only a hardware-specific device
+driver which provides a character device interface to send and
+receive raw CAN frames, directly to/from the controller hardware.
+Queueing of frames and higher-level transport protocols like ISO-TP
+have to be implemented in user space applications.  Also, most
+character-device implementations support only one single process to
+open the device at a time, similar to a serial interface.  Exchanging
+the CAN controller requires employment of another device driver and
+often the need for adaption of large parts of the application to the
+new driver's API.
+
+SocketCAN was designed to overcome all of these limitations.  A new
+protocol family has been implemented which provides a socket interface
+to user space applications and which builds upon the Linux network
+layer, enabling use all of the provided queueing functionality.  A device
+driver for CAN controller hardware registers itself with the Linux
+network layer as a network device, so that CAN frames from the
+controller can be passed up to the network layer and on to the CAN
+protocol family module and also vice-versa.  Also, the protocol family
+module provides an API for transport protocol modules to register, so
+that any number of transport protocols can be loaded or unloaded
+dynamically.  In fact, the can core module alone does not provide any
+protocol and cannot be used without loading at least one additional
+protocol module.  Multiple sockets can be opened at the same time,
+on different or the same protocol module and they can listen/send
+frames on different or the same CAN IDs.  Several sockets listening on
+the same interface for frames with the same CAN ID are all passed the
+same received matching CAN frames.  An application wishing to
+communicate using a specific transport protocol, e.g. ISO-TP, just
+selects that protocol when opening the socket, and then can read and
+write application data byte streams, without having to deal with
+CAN-IDs, frames, etc.
+
+Similar functionality visible from user-space could be provided by a
+character device, too, but this would lead to a technically inelegant
+solution for a couple of reasons:
+
+* **Intricate usage:**  Instead of passing a protocol argument to
+  socket(2) and using bind(2) to select a CAN interface and CAN ID, an
+  application would have to do all these operations using ioctl(2)s.
+
+* **Code duplication:**  A character device cannot make use of the Linux
+  network queueing code, so all that code would have to be duplicated
+  for CAN networking.
+
+* **Abstraction:**  In most existing character-device implementations, the
+  hardware-specific device driver for a CAN controller directly
+  provides the character device for the application to work with.
+  This is at least very unusual in Unix systems for both, char and
+  block devices.  For example you don't have a character device for a
+  certain UART of a serial interface, a certain sound chip in your
+  computer, a SCSI or IDE controller providing access to your hard
+  disk or tape streamer device.  Instead, you have abstraction layers
+  which provide a unified character or block device interface to the
+  application on the one hand, and a interface for hardware-specific
+  device drivers on the other hand.  These abstractions are provided
+  by subsystems like the tty layer, the audio subsystem or the SCSI
+  and IDE subsystems for the devices mentioned above.
+
+  The easiest way to implement a CAN device driver is as a character
+  device without such a (complete) abstraction layer, as is done by most
+  existing drivers.  The right way, however, would be to add such a
+  layer with all the functionality like registering for certain CAN
+  IDs, supporting several open file descriptors and (de)multiplexing
+  CAN frames between them, (sophisticated) queueing of CAN frames, and
+  providing an API for device drivers to register with.  However, then
+  it would be no more difficult, or may be even easier, to use the
+  networking framework provided by the Linux kernel, and this is what
+  SocketCAN does.
+
+The use of the networking framework of the Linux kernel is just the
+natural and most appropriate way to implement CAN for Linux.
+
+
+.. _socketcan-concept:
+
+SocketCAN Concept
+=================
+
+As described in :ref:`socketcan-motivation` the main goal of SocketCAN is to
+provide a socket interface to user space applications which builds
+upon the Linux network layer. In contrast to the commonly known
+TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
+medium that has no MAC-layer addressing like ethernet. The CAN-identifier
+(can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
+have to be chosen uniquely on the bus. When designing a CAN-ECU
+network the CAN-IDs are mapped to be sent by a specific ECU.
+For this reason a CAN-ID can be treated best as a kind of source address.
+
+
+.. _socketcan-receive-lists:
+
+Receive Lists
+-------------
+
+The network transparent access of multiple applications leads to the
+problem that different applications may be interested in the same
+CAN-IDs from the same CAN network interface. The SocketCAN core
+module - which implements the protocol family CAN - provides several
+high efficient receive lists for this reason. If e.g. a user space
+application opens a CAN RAW socket, the raw protocol module itself
+requests the (range of) CAN-IDs from the SocketCAN core that are
+requested by the user. The subscription and unsubscription of
+CAN-IDs can be done for specific CAN interfaces or for all(!) known
+CAN interfaces with the can_rx_(un)register() functions provided to
+CAN protocol modules by the SocketCAN core (see :ref:`socketcan-core-module`).
+To optimize the CPU usage at runtime the receive lists are split up
+into several specific lists per device that match the requested
+filter complexity for a given use-case.
+
+
+.. _socketcan-local-loopback1:
+
+Local Loopback of Sent Frames
+-----------------------------
+
+As known from other networking concepts the data exchanging
+applications may run on the same or different nodes without any
+change (except for the according addressing information):
+
+.. code::
+
+	 ___   ___   ___                   _______   ___
+	| _ | | _ | | _ |                 | _   _ | | _ |
+	||A|| ||B|| ||C||                 ||A| |B|| ||C||
+	|___| |___| |___|                 |_______| |___|
+	  |     |     |                       |       |
+	-----------------(1)- CAN bus -(2)---------------
+
+To ensure that application A receives the same information in the
+example (2) as it would receive in example (1) there is need for
+some kind of local loopback of the sent CAN frames on the appropriate
+node.
+
+The Linux network devices (by default) just can handle the
+transmission and reception of media dependent frames. Due to the
+arbitration on the CAN bus the transmission of a low prio CAN-ID
+may be delayed by the reception of a high prio CAN frame. To
+reflect the correct [#f1]_ traffic on the node the loopback of the sent
+data has to be performed right after a successful transmission. If
+the CAN network interface is not capable of performing the loopback for
+some reason the SocketCAN core can do this task as a fallback solution.
+See :ref:`socketcan-local-loopback1` for details (recommended).
+
+The loopback functionality is enabled by default to reflect standard
+networking behaviour for CAN applications. Due to some requests from
+the RT-SocketCAN group the loopback optionally may be disabled for each
+separate socket. See sockopts from the CAN RAW sockets in :ref:`socketcan-raw-sockets`.
+
+.. [#f1] you really like to have this when you're running analyser
+       tools like 'candump' or 'cansniffer' on the (same) node.
+
+
+.. _socketcan-network-problem-notifications:
+
+Network Problem Notifications
+-----------------------------
+
+The use of the CAN bus may lead to several problems on the physical
+and media access control layer. Detecting and logging of these lower
+layer problems is a vital requirement for CAN users to identify
+hardware issues on the physical transceiver layer as well as
+arbitration problems and error frames caused by the different
+ECUs. The occurrence of detected errors are important for diagnosis
+and have to be logged together with the exact timestamp. For this
+reason the CAN interface driver can generate so called Error Message
+Frames that can optionally be passed to the user application in the
+same way as other CAN frames. Whenever an error on the physical layer
+or the MAC layer is detected (e.g. by the CAN controller) the driver
+creates an appropriate error message frame. Error messages frames can
+be requested by the user application using the common CAN filter
+mechanisms. Inside this filter definition the (interested) type of
+errors may be selected. The reception of error messages is disabled
+by default. The format of the CAN error message frame is briefly
+described in the Linux header file "include/uapi/linux/can/error.h".
+
+
+How to use SocketCAN
+====================
+
+Like TCP/IP, you first need to open a socket for communicating over a
+CAN network. Since SocketCAN implements a new protocol family, you
+need to pass PF_CAN as the first argument to the socket(2) system
+call. Currently, there are two CAN protocols to choose from, the raw
+socket protocol and the broadcast manager (BCM). So to open a socket,
+you would write::
+
+    s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
+
+and::
+
+    s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
+
+respectively.  After the successful creation of the socket, you would
+normally use the bind(2) system call to bind the socket to a CAN
+interface (which is different from TCP/IP due to different addressing
+- see :ref:`socketcan-concept`). After binding (CAN_RAW) or connecting (CAN_BCM)
+the socket, you can read(2) and write(2) from/to the socket or use
+send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
+on the socket as usual. There are also CAN specific socket options
+described below.
+
+The basic CAN frame structure and the sockaddr structure are defined
+in include/linux/can.h:
+
+.. code-block:: C
+
+    struct can_frame {
+            canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
+            __u8    can_dlc; /* frame payload length in byte (0 .. 8) */
+            __u8    __pad;   /* padding */
+            __u8    __res0;  /* reserved / padding */
+            __u8    __res1;  /* reserved / padding */
+            __u8    data[8] __attribute__((aligned(8)));
+    };
+
+The alignment of the (linear) payload data[] to a 64bit boundary
+allows the user to define their own structs and unions to easily access
+the CAN payload. There is no given byteorder on the CAN bus by
+default. A read(2) system call on a CAN_RAW socket transfers a
+struct can_frame to the user space.
+
+The sockaddr_can structure has an interface index like the
+PF_PACKET socket, that also binds to a specific interface:
+
+.. code-block:: C
+
+    struct sockaddr_can {
+            sa_family_t can_family;
+            int         can_ifindex;
+            union {
+                    /* transport protocol class address info (e.g. ISOTP) */
+                    struct { canid_t rx_id, tx_id; } tp;
+
+                    /* reserved for future CAN protocols address information */
+            } can_addr;
+    };
+
+To determine the interface index an appropriate ioctl() has to
+be used (example for CAN_RAW sockets without error checking):
+
+.. code-block:: C
+
+    int s;
+    struct sockaddr_can addr;
+    struct ifreq ifr;
+
+    s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
+
+    strcpy(ifr.ifr_name, "can0" );
+    ioctl(s, SIOCGIFINDEX, &ifr);
+
+    addr.can_family = AF_CAN;
+    addr.can_ifindex = ifr.ifr_ifindex;
+
+    bind(s, (struct sockaddr *)&addr, sizeof(addr));
+
+    (..)
+
+To bind a socket to all(!) CAN interfaces the interface index must
+be 0 (zero). In this case the socket receives CAN frames from every
+enabled CAN interface. To determine the originating CAN interface
+the system call recvfrom(2) may be used instead of read(2). To send
+on a socket that is bound to 'any' interface sendto(2) is needed to
+specify the outgoing interface.
+
+Reading CAN frames from a bound CAN_RAW socket (see above) consists
+of reading a struct can_frame:
+
+.. code-block:: C
+
+    struct can_frame frame;
+
+    nbytes = read(s, &frame, sizeof(struct can_frame));
+
+    if (nbytes < 0) {
+            perror("can raw socket read");
+            return 1;
+    }
+
+    /* paranoid check ... */
+    if (nbytes < sizeof(struct can_frame)) {
+            fprintf(stderr, "read: incomplete CAN frame\n");
+            return 1;
+    }
+
+    /* do something with the received CAN frame */
+
+Writing CAN frames can be done similarly, with the write(2) system call::
+
+    nbytes = write(s, &frame, sizeof(struct can_frame));
+
+When the CAN interface is bound to 'any' existing CAN interface
+(addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
+information about the originating CAN interface is needed:
+
+.. code-block:: C
+
+    struct sockaddr_can addr;
+    struct ifreq ifr;
+    socklen_t len = sizeof(addr);
+    struct can_frame frame;
+
+    nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
+                      0, (struct sockaddr*)&addr, &len);
+
+    /* get interface name of the received CAN frame */
+    ifr.ifr_ifindex = addr.can_ifindex;
+    ioctl(s, SIOCGIFNAME, &ifr);
+    printf("Received a CAN frame from interface %s", ifr.ifr_name);
+
+To write CAN frames on sockets bound to 'any' CAN interface the
+outgoing interface has to be defined certainly:
+
+.. code-block:: C
+
+    strcpy(ifr.ifr_name, "can0");
+    ioctl(s, SIOCGIFINDEX, &ifr);
+    addr.can_ifindex = ifr.ifr_ifindex;
+    addr.can_family  = AF_CAN;
+
+    nbytes = sendto(s, &frame, sizeof(struct can_frame),
+                    0, (struct sockaddr*)&addr, sizeof(addr));
+
+An accurate timestamp can be obtained with an ioctl(2) call after reading
+a message from the socket:
+
+.. code-block:: C
+
+    struct timeval tv;
+    ioctl(s, SIOCGSTAMP, &tv);
+
+The timestamp has a resolution of one microsecond and is set automatically
+at the reception of a CAN frame.
+
+Remark about CAN FD (flexible data rate) support:
+
+Generally the handling of CAN FD is very similar to the formerly described
+examples. The new CAN FD capable CAN controllers support two different
+bitrates for the arbitration phase and the payload phase of the CAN FD frame
+and up to 64 bytes of payload. This extended payload length breaks all the
+kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
+bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
+the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
+switches the socket into a mode that allows the handling of CAN FD frames
+and (legacy) CAN frames simultaneously (see :ref:`socketcan-rawfd`).
+
+The struct canfd_frame is defined in include/linux/can.h:
+
+.. code-block:: C
+
+    struct canfd_frame {
+            canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
+            __u8    len;     /* frame payload length in byte (0 .. 64) */
+            __u8    flags;   /* additional flags for CAN FD */
+            __u8    __res0;  /* reserved / padding */
+            __u8    __res1;  /* reserved / padding */
+            __u8    data[64] __attribute__((aligned(8)));
+    };
+
+The struct canfd_frame and the existing struct can_frame have the can_id,
+the payload length and the payload data at the same offset inside their
+structures. This allows to handle the different structures very similar.
+When the content of a struct can_frame is copied into a struct canfd_frame
+all structure elements can be used as-is - only the data[] becomes extended.
+
+When introducing the struct canfd_frame it turned out that the data length
+code (DLC) of the struct can_frame was used as a length information as the
+length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
+the easy handling of the length information the canfd_frame.len element
+contains a plain length value from 0 .. 64. So both canfd_frame.len and
+can_frame.can_dlc are equal and contain a length information and no DLC.
+For details about the distinction of CAN and CAN FD capable devices and
+the mapping to the bus-relevant data length code (DLC), see :ref:`socketcan-can-fd-driver`.
+
+The length of the two CAN(FD) frame structures define the maximum transfer
+unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
+definitions are specified for CAN specific MTUs in include/linux/can.h:
+
+.. code-block:: C
+
+  #define CAN_MTU   (sizeof(struct can_frame))   == 16  => 'legacy' CAN frame
+  #define CANFD_MTU (sizeof(struct canfd_frame)) == 72  => CAN FD frame
+
+
+.. _socketcan-raw-sockets:
+
+RAW Protocol Sockets with can_filters (SOCK_RAW)
+------------------------------------------------
+
+Using CAN_RAW sockets is extensively comparable to the commonly
+known access to CAN character devices. To meet the new possibilities
+provided by the multi user SocketCAN approach, some reasonable
+defaults are set at RAW socket binding time:
+
+- The filters are set to exactly one filter receiving everything
+- The socket only receives valid data frames (=> no error message frames)
+- The loopback of sent CAN frames is enabled (see :ref:`socketcan-local-loopback2`)
+- The socket does not receive its own sent frames (in loopback mode)
+
+These default settings may be changed before or after binding the socket.
+To use the referenced definitions of the socket options for CAN_RAW
+sockets, include <linux/can/raw.h>.
+
+
+.. _socketcan-rawfilter:
+
+RAW socket option CAN_RAW_FILTER
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The reception of CAN frames using CAN_RAW sockets can be controlled
+by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
+
+The CAN filter structure is defined in include/linux/can.h:
+
+.. code-block:: C
+
+    struct can_filter {
+            canid_t can_id;
+            canid_t can_mask;
+    };
+
+A filter matches, when:
+
+.. code-block:: C
+
+    <received_can_id> & mask == can_id & mask
+
+which is analogous to known CAN controllers hardware filter semantics.
+The filter can be inverted in this semantic, when the CAN_INV_FILTER
+bit is set in can_id element of the can_filter structure. In
+contrast to CAN controller hardware filters the user may set 0 .. n
+receive filters for each open socket separately:
+
+.. code-block:: C
+
+    struct can_filter rfilter[2];
+
+    rfilter[0].can_id   = 0x123;
+    rfilter[0].can_mask = CAN_SFF_MASK;
+    rfilter[1].can_id   = 0x200;
+    rfilter[1].can_mask = 0x700;
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
+
+To disable the reception of CAN frames on the selected CAN_RAW socket:
+
+.. code-block:: C
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
+
+To set the filters to zero filters is quite obsolete as to not read
+data causes the raw socket to discard the received CAN frames. But
+having this 'send only' use-case we may remove the receive list in the
+Kernel to save a little (really a very little!) CPU usage.
+
+CAN Filter Usage Optimisation
+.............................
+
+The CAN filters are processed in per-device filter lists at CAN frame
+reception time. To reduce the number of checks that need to be performed
+while walking through the filter lists the CAN core provides an optimized
+filter handling when the filter subscription focusses on a single CAN ID.
+
+For the possible 2048 SFF CAN identifiers the identifier is used as an index
+to access the corresponding subscription list without any further checks.
+For the 2^29 possible EFF CAN identifiers a 10 bit XOR folding is used as
+hash function to retrieve the EFF table index.
+
+To benefit from the optimized filters for single CAN identifiers the
+CAN_SFF_MASK or CAN_EFF_MASK have to be set into can_filter.mask together
+with set CAN_EFF_FLAG and CAN_RTR_FLAG bits. A set CAN_EFF_FLAG bit in the
+can_filter.mask makes clear that it matters whether a SFF or EFF CAN ID is
+subscribed. E.g. in the example from above:
+
+.. code-block:: C
+
+    rfilter[0].can_id   = 0x123;
+    rfilter[0].can_mask = CAN_SFF_MASK;
+
+both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass.
+
+To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the
+filter has to be defined in this way to benefit from the optimized filters:
+
+.. code-block:: C
+
+    struct can_filter rfilter[2];
+
+    rfilter[0].can_id   = 0x123;
+    rfilter[0].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_SFF_MASK);
+    rfilter[1].can_id   = 0x12345678 | CAN_EFF_FLAG;
+    rfilter[1].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_EFF_MASK);
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
+
+
+RAW Socket Option CAN_RAW_ERR_FILTER
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+As described in :ref:`socketcan-network-problem-notifications` the CAN interface driver can generate so
+called Error Message Frames that can optionally be passed to the user
+application in the same way as other CAN frames. The possible
+errors are divided into different error classes that may be filtered
+using the appropriate error mask. To register for every possible
+error condition CAN_ERR_MASK can be used as value for the error mask.
+The values for the error mask are defined in linux/can/error.h:
+
+.. code-block:: C
+
+    can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
+               &err_mask, sizeof(err_mask));
+
+
+RAW Socket Option CAN_RAW_LOOPBACK
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To meet multi user needs the local loopback is enabled by default
+(see :ref:`socketcan-local-loopback1` for details). But in some embedded use-cases
+(e.g. when only one application uses the CAN bus) this loopback
+functionality can be disabled (separately for each socket):
+
+.. code-block:: C
+
+    int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
+
+
+RAW socket option CAN_RAW_RECV_OWN_MSGS
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When the local loopback is enabled, all the sent CAN frames are
+looped back to the open CAN sockets that registered for the CAN
+frames' CAN-ID on this given interface to meet the multi user
+needs. The reception of the CAN frames on the same socket that was
+sending the CAN frame is assumed to be unwanted and therefore
+disabled by default. This default behaviour may be changed on
+demand:
+
+.. code-block:: C
+
+    int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
+               &recv_own_msgs, sizeof(recv_own_msgs));
+
+
+.. _socketcan-rawfd:
+
+RAW Socket Option CAN_RAW_FD_FRAMES
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+CAN FD support in CAN_RAW sockets can be enabled with a new socket option
+CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
+not supported by the CAN_RAW socket (e.g. on older kernels), switching the
+CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
+
+Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
+and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
+when reading from the socket:
+
+.. code-block:: C
+
+    CAN_RAW_FD_FRAMES enabled:  CAN_MTU and CANFD_MTU are allowed
+    CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
+
+Example:
+
+.. code-block:: C
+
+    [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
+
+    struct canfd_frame cfd;
+
+    nbytes = read(s, &cfd, CANFD_MTU);
+
+    if (nbytes == CANFD_MTU) {
+            printf("got CAN FD frame with length %d\n", cfd.len);
+            /* cfd.flags contains valid data */
+    } else if (nbytes == CAN_MTU) {
+            printf("got legacy CAN frame with length %d\n", cfd.len);
+            /* cfd.flags is undefined */
+    } else {
+            fprintf(stderr, "read: invalid CAN(FD) frame\n");
+            return 1;
+    }
+
+    /* the content can be handled independently from the received MTU size */
+
+    printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
+    for (i = 0; i < cfd.len; i++)
+            printf("%02X ", cfd.data[i]);
+
+When reading with size CANFD_MTU only returns CAN_MTU bytes that have
+been received from the socket a legacy CAN frame has been read into the
+provided CAN FD structure. Note that the canfd_frame.flags data field is
+not specified in the struct can_frame and therefore it is only valid in
+CANFD_MTU sized CAN FD frames.
+
+Implementation hint for new CAN applications:
+
+To build a CAN FD aware application use struct canfd_frame as basic CAN
+data structure for CAN_RAW based applications. When the application is
+executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
+socket option returns an error: No problem. You'll get legacy CAN frames
+or CAN FD frames and can process them the same way.
+
+When sending to CAN devices make sure that the device is capable to handle
+CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
+The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
+
+
+RAW socket option CAN_RAW_JOIN_FILTERS
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The CAN_RAW socket can set multiple CAN identifier specific filters that
+lead to multiple filters in the af_can.c filter processing. These filters
+are indenpendent from each other which leads to logical OR'ed filters when
+applied (see :ref:`socketcan-rawfilter`).
+
+This socket option joines the given CAN filters in the way that only CAN
+frames are passed to user space that matched *all* given CAN filters. The
+semantic for the applied filters is therefore changed to a logical AND.
+
+This is useful especially when the filterset is a combination of filters
+where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
+CAN ID ranges from the incoming traffic.
+
+
+RAW Socket Returned Message Flags
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When using recvmsg() call, the msg->msg_flags may contain following flags:
+
+MSG_DONTROUTE:
+	set when the received frame was created on the local host.
+
+MSG_CONFIRM:
+	set when the frame was sent via the socket it is received on.
+	This flag can be interpreted as a 'transmission confirmation' when the
+	CAN driver supports the echo of frames on driver level, see
+	:ref:`socketcan-local-loopback1` and :ref:`socketcan-local-loopback2`.
+	In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
+
+
+Broadcast Manager Protocol Sockets (SOCK_DGRAM)
+-----------------------------------------------
+
+The Broadcast Manager protocol provides a command based configuration
+interface to filter and send (e.g. cyclic) CAN messages in kernel space.
+
+Receive filters can be used to down sample frequent messages; detect events
+such as message contents changes, packet length changes, and do time-out
+monitoring of received messages.
+
+Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
+created and modified at runtime; both the message content and the two
+possible transmit intervals can be altered.
+
+A BCM socket is not intended for sending individual CAN frames using the
+struct can_frame as known from the CAN_RAW socket. Instead a special BCM
+configuration message is defined. The basic BCM configuration message used
+to communicate with the broadcast manager and the available operations are
+defined in the linux/can/bcm.h include. The BCM message consists of a
+message header with a command ('opcode') followed by zero or more CAN frames.
+The broadcast manager sends responses to user space in the same form:
+
+.. code-block:: C
+
+    struct bcm_msg_head {
+            __u32 opcode;                   /* command */
+            __u32 flags;                    /* special flags */
+            __u32 count;                    /* run 'count' times with ival1 */
+            struct timeval ival1, ival2;    /* count and subsequent interval */
+            canid_t can_id;                 /* unique can_id for task */
+            __u32 nframes;                  /* number of can_frames following */
+            struct can_frame frames[0];
+    };
+
+The aligned payload 'frames' uses the same basic CAN frame structure defined
+at the beginning of :ref:`socketcan-rawfd` and in the include/linux/can.h include. All
+messages to the broadcast manager from user space have this structure.
+
+Note a CAN_BCM socket must be connected instead of bound after socket
+creation (example without error checking):
+
+.. code-block:: C
+
+    int s;
+    struct sockaddr_can addr;
+    struct ifreq ifr;
+
+    s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
+
+    strcpy(ifr.ifr_name, "can0");
+    ioctl(s, SIOCGIFINDEX, &ifr);
+
+    addr.can_family = AF_CAN;
+    addr.can_ifindex = ifr.ifr_ifindex;
+
+    connect(s, (struct sockaddr *)&addr, sizeof(addr));
+
+    (..)
+
+The broadcast manager socket is able to handle any number of in flight
+transmissions or receive filters concurrently. The different RX/TX jobs are
+distinguished by the unique can_id in each BCM message. However additional
+CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
+When the broadcast manager socket is bound to 'any' CAN interface (=> the
+interface index is set to zero) the configured receive filters apply to any
+CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
+interface index. When using recvfrom() instead of read() to retrieve BCM
+socket messages the originating CAN interface is provided in can_ifindex.
+
+
+Broadcast Manager Operations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The opcode defines the operation for the broadcast manager to carry out,
+or details the broadcast managers response to several events, including
+user requests.
+
+Transmit Operations (user space to broadcast manager):
+
+TX_SETUP:
+	Create (cyclic) transmission task.
+
+TX_DELETE:
+	Remove (cyclic) transmission task, requires only can_id.
+
+TX_READ:
+	Read properties of (cyclic) transmission task for can_id.
+
+TX_SEND:
+	Send one CAN frame.
+
+Transmit Responses (broadcast manager to user space):
+
+TX_STATUS:
+	Reply to TX_READ request (transmission task configuration).
+
+TX_EXPIRED:
+	Notification when counter finishes sending at initial interval
+	'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
+
+Receive Operations (user space to broadcast manager):
+
+RX_SETUP:
+	Create RX content filter subscription.
+
+RX_DELETE:
+	Remove RX content filter subscription, requires only can_id.
+
+RX_READ:
+	Read properties of RX content filter subscription for can_id.
+
+Receive Responses (broadcast manager to user space):
+
+RX_STATUS:
+	Reply to RX_READ request (filter task configuration).
+
+RX_TIMEOUT:
+	Cyclic message is detected to be absent (timer ival1 expired).
+
+RX_CHANGED:
+	BCM message with updated CAN frame (detected content change).
+	Sent on first message received or on receipt of revised CAN messages.
+
+
+Broadcast Manager Message Flags
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When sending a message to the broadcast manager the 'flags' element may
+contain the following flag definitions which influence the behaviour:
+
+SETTIMER:
+	Set the values of ival1, ival2 and count
+
+STARTTIMER:
+	Start the timer with the actual values of ival1, ival2
+	and count. Starting the timer leads simultaneously to emit a CAN frame.
+
+TX_COUNTEVT:
+	Create the message TX_EXPIRED when count expires
+
+TX_ANNOUNCE:
+	A change of data by the process is emitted immediately.
+
+TX_CP_CAN_ID:
+	Copies the can_id from the message header to each
+	subsequent frame in frames. This is intended as usage simplification. For
+	TX tasks the unique can_id from the message header may differ from the
+	can_id(s) stored for transmission in the subsequent struct can_frame(s).
+
+RX_FILTER_ID:
+	Filter by can_id alone, no frames required (nframes=0).
+
+RX_CHECK_DLC:
+	A change of the DLC leads to an RX_CHANGED.
+
+RX_NO_AUTOTIMER:
+	Prevent automatically starting the timeout monitor.
+
+RX_ANNOUNCE_RESUME:
+	If passed at RX_SETUP and a receive timeout occurred, a
+	RX_CHANGED message will be generated when the (cyclic) receive restarts.
+
+TX_RESET_MULTI_IDX:
+	Reset the index for the multiple frame transmission.
+
+RX_RTR_FRAME:
+	Send reply for RTR-request (placed in op->frames[0]).
+
+
+Broadcast Manager Transmission Timers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Periodic transmission configurations may use up to two interval timers.
+In this case the BCM sends a number of messages ('count') at an interval
+'ival1', then continuing to send at another given interval 'ival2'. When
+only one timer is needed 'count' is set to zero and only 'ival2' is used.
+When SET_TIMER and START_TIMER flag were set the timers are activated.
+The timer values can be altered at runtime when only SET_TIMER is set.
+
+
+Broadcast Manager message sequence transmission
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
+TX task configuration. The number of CAN frames is provided in the 'nframes'
+element of the BCM message head. The defined number of CAN frames are added
+as array to the TX_SETUP BCM configuration message:
+
+.. code-block:: C
+
+    /* create a struct to set up a sequence of four CAN frames */
+    struct {
+            struct bcm_msg_head msg_head;
+            struct can_frame frame[4];
+    } mytxmsg;
+
+    (..)
+    mytxmsg.msg_head.nframes = 4;
+    (..)
+
+    write(s, &mytxmsg, sizeof(mytxmsg));
+
+With every transmission the index in the array of CAN frames is increased
+and set to zero at index overflow.
+
+
+Broadcast Manager Receive Filter Timers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
+When the SET_TIMER flag is set the timers are enabled:
+
+ival1:
+	Send RX_TIMEOUT when a received message is not received again within
+	the given time. When START_TIMER is set at RX_SETUP the timeout detection
+	is activated directly - even without a former CAN frame reception.
+
+ival2:
+	Throttle the received message rate down to the value of ival2. This
+	is useful to reduce messages for the application when the signal inside the
+	CAN frame is stateless as state changes within the ival2 periode may get
+	lost.
+
+Broadcast Manager Multiplex Message Receive Filter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To filter for content changes in multiplex message sequences an array of more
+than one CAN frames can be passed in a RX_SETUP configuration message. The
+data bytes of the first CAN frame contain the mask of relevant bits that
+have to match in the subsequent CAN frames with the received CAN frame.
+If one of the subsequent CAN frames is matching the bits in that frame data
+mark the relevant content to be compared with the previous received content.
+Up to 257 CAN frames (multiplex filter bit mask CAN frame plus 256 CAN
+filters) can be added as array to the TX_SETUP BCM configuration message:
+
+.. code-block:: C
+
+    /* usually used to clear CAN frame data[] - beware of endian problems! */
+    #define U64_DATA(p) (*(unsigned long long*)(p)->data)
+
+    struct {
+            struct bcm_msg_head msg_head;
+            struct can_frame frame[5];
+    } msg;
+
+    msg.msg_head.opcode  = RX_SETUP;
+    msg.msg_head.can_id  = 0x42;
+    msg.msg_head.flags   = 0;
+    msg.msg_head.nframes = 5;
+    U64_DATA(&msg.frame[0]) = 0xFF00000000000000ULL; /* MUX mask */
+    U64_DATA(&msg.frame[1]) = 0x01000000000000FFULL; /* data mask (MUX 0x01) */
+    U64_DATA(&msg.frame[2]) = 0x0200FFFF000000FFULL; /* data mask (MUX 0x02) */
+    U64_DATA(&msg.frame[3]) = 0x330000FFFFFF0003ULL; /* data mask (MUX 0x33) */
+    U64_DATA(&msg.frame[4]) = 0x4F07FC0FF0000000ULL; /* data mask (MUX 0x4F) */
+
+    write(s, &msg, sizeof(msg));
+
+
+Broadcast Manager CAN FD Support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The programming API of the CAN_BCM depends on struct can_frame which is
+given as array directly behind the bcm_msg_head structure. To follow this
+schema for the CAN FD frames a new flag 'CAN_FD_FRAME' in the bcm_msg_head
+flags indicates that the concatenated CAN frame structures behind the
+bcm_msg_head are defined as struct canfd_frame:
+
+.. code-block:: C
+
+    struct {
+            struct bcm_msg_head msg_head;
+            struct canfd_frame frame[5];
+    } msg;
+
+    msg.msg_head.opcode  = RX_SETUP;
+    msg.msg_head.can_id  = 0x42;
+    msg.msg_head.flags   = CAN_FD_FRAME;
+    msg.msg_head.nframes = 5;
+    (..)
+
+When using CAN FD frames for multiplex filtering the MUX mask is still
+expected in the first 64 bit of the struct canfd_frame data section.
+
+
+Connected Transport Protocols (SOCK_SEQPACKET)
+----------------------------------------------
+
+(to be written)
+
+
+Unconnected Transport Protocols (SOCK_DGRAM)
+--------------------------------------------
+
+(to be written)
+
+
+.. _socketcan-core-module:
+
+SocketCAN Core Module
+=====================
+
+The SocketCAN core module implements the protocol family
+PF_CAN. CAN protocol modules are loaded by the core module at
+runtime. The core module provides an interface for CAN protocol
+modules to subscribe needed CAN IDs (see :ref:`socketcan-receive-lists`).
+
+
+can.ko Module Params
+--------------------
+
+- **stats_timer**:
+  To calculate the SocketCAN core statistics
+  (e.g. current/maximum frames per second) this 1 second timer is
+  invoked at can.ko module start time by default. This timer can be
+  disabled by using stattimer=0 on the module commandline.
+
+- **debug**:
+  (removed since SocketCAN SVN r546)
+
+
+procfs content
+--------------
+
+As described in :ref:`socketcan-receive-lists` the SocketCAN core uses several filter
+lists to deliver received CAN frames to CAN protocol modules. These
+receive lists, their filters and the count of filter matches can be
+checked in the appropriate receive list. All entries contain the
+device and a protocol module identifier::
+
+    foo@bar:~$ cat /proc/net/can/rcvlist_all
+
+    receive list 'rx_all':
+      (vcan3: no entry)
+      (vcan2: no entry)
+      (vcan1: no entry)
+      device   can_id   can_mask  function  userdata   matches  ident
+       vcan0     000    00000000  f88e6370  f6c6f400         0  raw
+      (any: no entry)
+
+In this example an application requests any CAN traffic from vcan0::
+
+    rcvlist_all - list for unfiltered entries (no filter operations)
+    rcvlist_eff - list for single extended frame (EFF) entries
+    rcvlist_err - list for error message frames masks
+    rcvlist_fil - list for mask/value filters
+    rcvlist_inv - list for mask/value filters (inverse semantic)
+    rcvlist_sff - list for single standard frame (SFF) entries
+
+Additional procfs files in /proc/net/can::
+
+    stats       - SocketCAN core statistics (rx/tx frames, match ratios, ...)
+    reset_stats - manual statistic reset
+    version     - prints the SocketCAN core version and the ABI version
+
+
+Writing Own CAN Protocol Modules
+--------------------------------
+
+To implement a new protocol in the protocol family PF_CAN a new
+protocol has to be defined in include/linux/can.h .
+The prototypes and definitions to use the SocketCAN core can be
+accessed by including include/linux/can/core.h .
+In addition to functions that register the CAN protocol and the
+CAN device notifier chain there are functions to subscribe CAN
+frames received by CAN interfaces and to send CAN frames::
+
+    can_rx_register   - subscribe CAN frames from a specific interface
+    can_rx_unregister - unsubscribe CAN frames from a specific interface
+    can_send          - transmit a CAN frame (optional with local loopback)
+
+For details see the kerneldoc documentation in net/can/af_can.c or
+the source code of net/can/raw.c or net/can/bcm.c .
+
+
+CAN Network Drivers
+===================
+
+Writing a CAN network device driver is much easier than writing a
+CAN character device driver. Similar to other known network device
+drivers you mainly have to deal with:
+
+- TX: Put the CAN frame from the socket buffer to the CAN controller.
+- RX: Put the CAN frame from the CAN controller to the socket buffer.
+
+See e.g. at Documentation/networking/netdevices.txt . The differences
+for writing CAN network device driver are described below:
+
+
+General Settings
+----------------
+
+.. code-block:: C
+
+    dev->type  = ARPHRD_CAN; /* the netdevice hardware type */
+    dev->flags = IFF_NOARP;  /* CAN has no arp */
+
+    dev->mtu = CAN_MTU; /* sizeof(struct can_frame) -> legacy CAN interface */
+
+    or alternative, when the controller supports CAN with flexible data rate:
+    dev->mtu = CANFD_MTU; /* sizeof(struct canfd_frame) -> CAN FD interface */
+
+The struct can_frame or struct canfd_frame is the payload of each socket
+buffer (skbuff) in the protocol family PF_CAN.
+
+
+.. _socketcan-local-loopback2:
+
+Local Loopback of Sent Frames
+-----------------------------
+
+As described in :ref:`socketcan-local-loopback1` the CAN network device driver should
+support a local loopback functionality similar to the local echo
+e.g. of tty devices. In this case the driver flag IFF_ECHO has to be
+set to prevent the PF_CAN core from locally echoing sent frames
+(aka loopback) as fallback solution::
+
+    dev->flags = (IFF_NOARP | IFF_ECHO);
+
+
+CAN Controller Hardware Filters
+-------------------------------
+
+To reduce the interrupt load on deep embedded systems some CAN
+controllers support the filtering of CAN IDs or ranges of CAN IDs.
+These hardware filter capabilities vary from controller to
+controller and have to be identified as not feasible in a multi-user
+networking approach. The use of the very controller specific
+hardware filters could make sense in a very dedicated use-case, as a
+filter on driver level would affect all users in the multi-user
+system. The high efficient filter sets inside the PF_CAN core allow
+to set different multiple filters for each socket separately.
+Therefore the use of hardware filters goes to the category 'handmade
+tuning on deep embedded systems'. The author is running a MPC603e
+@133MHz with four SJA1000 CAN controllers from 2002 under heavy bus
+load without any problems ...
+
+
+The Virtual CAN Driver (vcan)
+-----------------------------
+
+Similar to the network loopback devices, vcan offers a virtual local
+CAN interface. A full qualified address on CAN consists of
+
+- a unique CAN Identifier (CAN ID)
+- the CAN bus this CAN ID is transmitted on (e.g. can0)
+
+so in common use cases more than one virtual CAN interface is needed.
+
+The virtual CAN interfaces allow the transmission and reception of CAN
+frames without real CAN controller hardware. Virtual CAN network
+devices are usually named 'vcanX', like vcan0 vcan1 vcan2 ...
+When compiled as a module the virtual CAN driver module is called vcan.ko
+
+Since Linux Kernel version 2.6.24 the vcan driver supports the Kernel
+netlink interface to create vcan network devices. The creation and
+removal of vcan network devices can be managed with the ip(8) tool::
+
+  - Create a virtual CAN network interface:
+       $ ip link add type vcan
+
+  - Create a virtual CAN network interface with a specific name 'vcan42':
+       $ ip link add dev vcan42 type vcan
+
+  - Remove a (virtual CAN) network interface 'vcan42':
+       $ ip link del vcan42
+
+
+The CAN Network Device Driver Interface
+---------------------------------------
+
+The CAN network device driver interface provides a generic interface
+to setup, configure and monitor CAN network devices. The user can then
+configure the CAN device, like setting the bit-timing parameters, via
+the netlink interface using the program "ip" from the "IPROUTE2"
+utility suite. The following chapter describes briefly how to use it.
+Furthermore, the interface uses a common data structure and exports a
+set of common functions, which all real CAN network device drivers
+should use. Please have a look to the SJA1000 or MSCAN driver to
+understand how to use them. The name of the module is can-dev.ko.
+
+
+Netlink interface to set/get devices properties
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The CAN device must be configured via netlink interface. The supported
+netlink message types are defined and briefly described in
+"include/linux/can/netlink.h". CAN link support for the program "ip"
+of the IPROUTE2 utility suite is available and it can be used as shown
+below:
+
+Setting CAN device properties::
+
+    $ ip link set can0 type can help
+    Usage: ip link set DEVICE type can
+        [ bitrate BITRATE [ sample-point SAMPLE-POINT] ] |
+        [ tq TQ prop-seg PROP_SEG phase-seg1 PHASE-SEG1
+          phase-seg2 PHASE-SEG2 [ sjw SJW ] ]
+
+        [ dbitrate BITRATE [ dsample-point SAMPLE-POINT] ] |
+        [ dtq TQ dprop-seg PROP_SEG dphase-seg1 PHASE-SEG1
+          dphase-seg2 PHASE-SEG2 [ dsjw SJW ] ]
+
+        [ loopback { on | off } ]
+        [ listen-only { on | off } ]
+        [ triple-sampling { on | off } ]
+        [ one-shot { on | off } ]
+        [ berr-reporting { on | off } ]
+        [ fd { on | off } ]
+        [ fd-non-iso { on | off } ]
+        [ presume-ack { on | off } ]
+
+        [ restart-ms TIME-MS ]
+        [ restart ]
+
+        Where: BITRATE       := { 1..1000000 }
+               SAMPLE-POINT  := { 0.000..0.999 }
+               TQ            := { NUMBER }
+               PROP-SEG      := { 1..8 }
+               PHASE-SEG1    := { 1..8 }
+               PHASE-SEG2    := { 1..8 }
+               SJW           := { 1..4 }
+               RESTART-MS    := { 0 | NUMBER }
+
+Display CAN device details and statistics::
+
+    $ ip -details -statistics link show can0
+    2: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP qlen 10
+      link/can
+      can <TRIPLE-SAMPLING> state ERROR-ACTIVE restart-ms 100
+      bitrate 125000 sample_point 0.875
+      tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
+      sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
+      clock 8000000
+      re-started bus-errors arbit-lost error-warn error-pass bus-off
+      41         17457      0          41         42         41
+      RX: bytes  packets  errors  dropped overrun mcast
+      140859     17608    17457   0       0       0
+      TX: bytes  packets  errors  dropped carrier collsns
+      861        112      0       41      0       0
+
+More info to the above output:
+
+"<TRIPLE-SAMPLING>"
+	Shows the list of selected CAN controller modes: LOOPBACK,
+	LISTEN-ONLY, or TRIPLE-SAMPLING.
+
+"state ERROR-ACTIVE"
+	The current state of the CAN controller: "ERROR-ACTIVE",
+	"ERROR-WARNING", "ERROR-PASSIVE", "BUS-OFF" or "STOPPED"
+
+"restart-ms 100"
+	Automatic restart delay time. If set to a non-zero value, a
+	restart of the CAN controller will be triggered automatically
+	in case of a bus-off condition after the specified delay time
+	in milliseconds. By default it's off.
+
+"bitrate 125000 sample-point 0.875"
+	Shows the real bit-rate in bits/sec and the sample-point in the
+	range 0.000..0.999. If the calculation of bit-timing parameters
+	is enabled in the kernel (CONFIG_CAN_CALC_BITTIMING=y), the
+	bit-timing can be defined by setting the "bitrate" argument.
+	Optionally the "sample-point" can be specified. By default it's
+	0.000 assuming CIA-recommended sample-points.
+
+"tq 125 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1"
+	Shows the time quanta in ns, propagation segment, phase buffer
+	segment 1 and 2 and the synchronisation jump width in units of
+	tq. They allow to define the CAN bit-timing in a hardware
+	independent format as proposed by the Bosch CAN 2.0 spec (see
+	chapter 8 of http://www.semiconductors.bosch.de/pdf/can2spec.pdf).
+
+"sja1000: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1 clock 8000000"
+	Shows the bit-timing constants of the CAN controller, here the
+	"sja1000". The minimum and maximum values of the time segment 1
+	and 2, the synchronisation jump width in units of tq, the
+	bitrate pre-scaler and the CAN system clock frequency in Hz.
+	These constants could be used for user-defined (non-standard)
+	bit-timing calculation algorithms in user-space.
+
+"re-started bus-errors arbit-lost error-warn error-pass bus-off"
+	Shows the number of restarts, bus and arbitration lost errors,
+	and the state changes to the error-warning, error-passive and
+	bus-off state. RX overrun errors are listed in the "overrun"
+	field of the standard network statistics.
+
+Setting the CAN Bit-Timing
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The CAN bit-timing parameters can always be defined in a hardware
+independent format as proposed in the Bosch CAN 2.0 specification
+specifying the arguments "tq", "prop_seg", "phase_seg1", "phase_seg2"
+and "sjw"::
+
+    $ ip link set canX type can tq 125 prop-seg 6 \
+				phase-seg1 7 phase-seg2 2 sjw 1
+
+If the kernel option CONFIG_CAN_CALC_BITTIMING is enabled, CIA
+recommended CAN bit-timing parameters will be calculated if the bit-
+rate is specified with the argument "bitrate"::
+
+    $ ip link set canX type can bitrate 125000
+
+Note that this works fine for the most common CAN controllers with
+standard bit-rates but may *fail* for exotic bit-rates or CAN system
+clock frequencies. Disabling CONFIG_CAN_CALC_BITTIMING saves some
+space and allows user-space tools to solely determine and set the
+bit-timing parameters. The CAN controller specific bit-timing
+constants can be used for that purpose. They are listed by the
+following command::
+
+    $ ip -details link show can0
+    ...
+      sja1000: clock 8000000 tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
+
+
+Starting and Stopping the CAN Network Device
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+A CAN network device is started or stopped as usual with the command
+"ifconfig canX up/down" or "ip link set canX up/down". Be aware that
+you *must* define proper bit-timing parameters for real CAN devices
+before you can start it to avoid error-prone default settings::
+
+    $ ip link set canX up type can bitrate 125000
+
+A device may enter the "bus-off" state if too many errors occurred on
+the CAN bus. Then no more messages are received or sent. An automatic
+bus-off recovery can be enabled by setting the "restart-ms" to a
+non-zero value, e.g.::
+
+    $ ip link set canX type can restart-ms 100
+
+Alternatively, the application may realize the "bus-off" condition
+by monitoring CAN error message frames and do a restart when
+appropriate with the command::
+
+    $ ip link set canX type can restart
+
+Note that a restart will also create a CAN error message frame (see
+also :ref:`socketcan-network-problem-notifications`).
+
+
+.. _socketcan-can-fd-driver:
+
+CAN FD (Flexible Data Rate) Driver Support
+------------------------------------------
+
+CAN FD capable CAN controllers support two different bitrates for the
+arbitration phase and the payload phase of the CAN FD frame. Therefore a
+second bit timing has to be specified in order to enable the CAN FD bitrate.
+
+Additionally CAN FD capable CAN controllers support up to 64 bytes of
+payload. The representation of this length in can_frame.can_dlc and
+canfd_frame.len for userspace applications and inside the Linux network
+layer is a plain value from 0 .. 64 instead of the CAN 'data length code'.
+The data length code was a 1:1 mapping to the payload length in the legacy
+CAN frames anyway. The payload length to the bus-relevant DLC mapping is
+only performed inside the CAN drivers, preferably with the helper
+functions can_dlc2len() and can_len2dlc().
+
+The CAN netdevice driver capabilities can be distinguished by the network
+devices maximum transfer unit (MTU)::
+
+  MTU = 16 (CAN_MTU)   => sizeof(struct can_frame)   => 'legacy' CAN device
+  MTU = 72 (CANFD_MTU) => sizeof(struct canfd_frame) => CAN FD capable device
+
+The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
+N.B. CAN FD capable devices can also handle and send legacy CAN frames.
+
+When configuring CAN FD capable CAN controllers an additional 'data' bitrate
+has to be set. This bitrate for the data phase of the CAN FD frame has to be
+at least the bitrate which was configured for the arbitration phase. This
+second bitrate is specified analogue to the first bitrate but the bitrate
+setting keywords for the 'data' bitrate start with 'd' e.g. dbitrate,
+dsample-point, dsjw or dtq and similar settings. When a data bitrate is set
+within the configuration process the controller option "fd on" can be
+specified to enable the CAN FD mode in the CAN controller. This controller
+option also switches the device MTU to 72 (CANFD_MTU).
+
+The first CAN FD specification presented as whitepaper at the International
+CAN Conference 2012 needed to be improved for data integrity reasons.
+Therefore two CAN FD implementations have to be distinguished today:
+
+- ISO compliant:     The ISO 11898-1:2015 CAN FD implementation (default)
+- non-ISO compliant: The CAN FD implementation following the 2012 whitepaper
+
+Finally there are three types of CAN FD controllers:
+
+1. ISO compliant (fixed)
+2. non-ISO compliant (fixed, like the M_CAN IP core v3.0.1 in m_can.c)
+3. ISO/non-ISO CAN FD controllers (switchable, like the PEAK PCAN-USB FD)
+
+The current ISO/non-ISO mode is announced by the CAN controller driver via
+netlink and displayed by the 'ip' tool (controller option FD-NON-ISO).
+The ISO/non-ISO-mode can be altered by setting 'fd-non-iso {on|off}' for
+switchable CAN FD controllers only.
+
+Example configuring 500 kbit/s arbitration bitrate and 4 Mbit/s data bitrate::
+
+    $ ip link set can0 up type can bitrate 500000 sample-point 0.75 \
+                                   dbitrate 4000000 dsample-point 0.8 fd on
+    $ ip -details link show can0
+    5: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UNKNOWN \
+             mode DEFAULT group default qlen 10
+    link/can  promiscuity 0
+    can <FD> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
+          bitrate 500000 sample-point 0.750
+          tq 50 prop-seg 14 phase-seg1 15 phase-seg2 10 sjw 1
+          pcan_usb_pro_fd: tseg1 1..64 tseg2 1..16 sjw 1..16 brp 1..1024 \
+          brp-inc 1
+          dbitrate 4000000 dsample-point 0.800
+          dtq 12 dprop-seg 7 dphase-seg1 8 dphase-seg2 4 dsjw 1
+          pcan_usb_pro_fd: dtseg1 1..16 dtseg2 1..8 dsjw 1..4 dbrp 1..1024 \
+          dbrp-inc 1
+          clock 80000000
+
+Example when 'fd-non-iso on' is added on this switchable CAN FD adapter::
+
+   can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0
+
+
+Supported CAN Hardware
+----------------------
+
+Please check the "Kconfig" file in "drivers/net/can" to get an actual
+list of the support CAN hardware. On the SocketCAN project website
+(see :ref:`socketcan-resources`) there might be further drivers available, also for
+older kernel versions.
+
+
+.. _socketcan-resources:
+
+SocketCAN Resources
+===================
+
+The Linux CAN / SocketCAN project resources (project site / mailing list)
+are referenced in the MAINTAINERS file in the Linux source tree.
+Search for CAN NETWORK [LAYERS|DRIVERS].
+
+Credits
+=======
+
+- Oliver Hartkopp (PF_CAN core, filters, drivers, bcm, SJA1000 driver)
+- Urs Thuermann (PF_CAN core, kernel integration, socket interfaces, raw, vcan)
+- Jan Kizka (RT-SocketCAN core, Socket-API reconciliation)
+- Wolfgang Grandegger (RT-SocketCAN core & drivers, Raw Socket-API reviews, CAN device driver interface, MSCAN driver)
+- Robert Schwebel (design reviews, PTXdist integration)
+- Marc Kleine-Budde (design reviews, Kernel 2.6 cleanups, drivers)
+- Benedikt Spranger (reviews)
+- Thomas Gleixner (LKML reviews, coding style, posting hints)
+- Andrey Volkov (kernel subtree structure, ioctls, MSCAN driver)
+- Matthias Brukner (first SJA1000 CAN netdevice implementation Q2/2003)
+- Klaus Hitschler (PEAK driver integration)
+- Uwe Koppe (CAN netdevices with PF_PACKET approach)
+- Michael Schulze (driver layer loopback requirement, RT CAN drivers review)
+- Pavel Pisa (Bit-timing calculation)
+- Sascha Hauer (SJA1000 platform driver)
+- Sebastian Haas (SJA1000 EMS PCI driver)
+- Markus Plessing (SJA1000 EMS PCI driver)
+- Per Dalen (SJA1000 Kvaser PCI driver)
+- Sam Ravnborg (reviews, coding style, kbuild help)