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Diffstat (limited to 'Documentation/networking/caif')
| -rw-r--r-- | Documentation/networking/caif/caif.rst | 138 | ||||
| -rw-r--r-- | Documentation/networking/caif/index.rst | 12 | ||||
| -rw-r--r-- | Documentation/networking/caif/linux_caif.rst | 195 |
3 files changed, 345 insertions, 0 deletions
diff --git a/Documentation/networking/caif/caif.rst b/Documentation/networking/caif/caif.rst new file mode 100644 index 000000000..d922d419c --- /dev/null +++ b/Documentation/networking/caif/caif.rst @@ -0,0 +1,138 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: <isonum.txt> + + +================ +Using Linux CAIF +================ + + +:Copyright: |copy| ST-Ericsson AB 2010 + +:Author: Sjur Brendeland/ sjur.brandeland@stericsson.com + +Start +===== + +If you have compiled CAIF for modules do:: + + $modprobe crc_ccitt + $modprobe caif + $modprobe caif_socket + $modprobe chnl_net + + +Preparing the setup with a STE modem +==================================== + +If you are working on integration of CAIF you should make sure +that the kernel is built with module support. + +There are some things that need to be tweaked to get the host TTY correctly +set up to talk to the modem. +Since the CAIF stack is running in the kernel and we want to use the existing +TTY, we are installing our physical serial driver as a line discipline above +the TTY device. + +To achieve this we need to install the N_CAIF ldisc from user space. +The benefit is that we can hook up to any TTY. + +The use of Start-of-frame-extension (STX) must also be set as +module parameter "ser_use_stx". + +Normally Frame Checksum is always used on UART, but this is also provided as a +module parameter "ser_use_fcs". + +:: + + $ modprobe caif_serial ser_ttyname=/dev/ttyS0 ser_use_stx=yes + $ ifconfig caif_ttyS0 up + +PLEASE NOTE: + There is a limitation in Android shell. + It only accepts one argument to insmod/modprobe! + +Trouble shooting +================ + +There are debugfs parameters provided for serial communication. +/sys/kernel/debug/caif_serial/<tty-name>/ + +* ser_state: Prints the bit-mask status where + + - 0x02 means SENDING, this is a transient state. + - 0x10 means FLOW_OFF_SENT, i.e. the previous frame has not been sent + and is blocking further send operation. Flow OFF has been propagated + to all CAIF Channels using this TTY. + +* tty_status: Prints the bit-mask tty status information + + - 0x01 - tty->warned is on. + - 0x04 - tty->packed is on. + - 0x08 - tty->flow.tco_stopped is on. + - 0x10 - tty->hw_stopped is on. + - 0x20 - tty->flow.stopped is on. + +* last_tx_msg: Binary blob Prints the last transmitted frame. + + This can be printed with:: + + $od --format=x1 /sys/kernel/debug/caif_serial/<tty>/last_rx_msg. + + The first two tx messages sent look like this. Note: The initial + byte 02 is start of frame extension (STX) used for re-syncing + upon errors. + + - Enumeration:: + + 0000000 02 05 00 00 03 01 d2 02 + | | | | | | + STX(1) | | | | + Length(2)| | | + Control Channel(1) + Command:Enumeration(1) + Link-ID(1) + Checksum(2) + + - Channel Setup:: + + 0000000 02 07 00 00 00 21 a1 00 48 df + | | | | | | | | + STX(1) | | | | | | + Length(2)| | | | | + Control Channel(1) + Command:Channel Setup(1) + Channel Type(1) + Priority and Link-ID(1) + Endpoint(1) + Checksum(2) + +* last_rx_msg: Prints the last transmitted frame. + + The RX messages for LinkSetup look almost identical but they have the + bit 0x20 set in the command bit, and Channel Setup has added one byte + before Checksum containing Channel ID. + + NOTE: + Several CAIF Messages might be concatenated. The maximum debug + buffer size is 128 bytes. + +Error Scenarios +=============== + +- last_tx_msg contains channel setup message and last_rx_msg is empty -> + The host seems to be able to send over the UART, at least the CAIF ldisc get + notified that sending is completed. + +- last_tx_msg contains enumeration message and last_rx_msg is empty -> + The host is not able to send the message from UART, the tty has not been + able to complete the transmit operation. + +- if /sys/kernel/debug/caif_serial/<tty>/tty_status is non-zero there + might be problems transmitting over UART. + + E.g. host and modem wiring is not correct you will typically see + tty_status = 0x10 (hw_stopped) and ser_state = 0x10 (FLOW_OFF_SENT). + + You will probably see the enumeration message in last_tx_message + and empty last_rx_message. diff --git a/Documentation/networking/caif/index.rst b/Documentation/networking/caif/index.rst new file mode 100644 index 000000000..ec29b6f4b --- /dev/null +++ b/Documentation/networking/caif/index.rst @@ -0,0 +1,12 @@ +.. SPDX-License-Identifier: GPL-2.0 + +CAIF +==== + +Contents: + +.. toctree:: + :maxdepth: 2 + + linux_caif + caif diff --git a/Documentation/networking/caif/linux_caif.rst b/Documentation/networking/caif/linux_caif.rst new file mode 100644 index 000000000..a0480862a --- /dev/null +++ b/Documentation/networking/caif/linux_caif.rst @@ -0,0 +1,195 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: <isonum.txt> + +========== +Linux CAIF +========== + +Copyright |copy| ST-Ericsson AB 2010 + +:Author: Sjur Brendeland/ sjur.brandeland@stericsson.com +:License terms: GNU General Public License (GPL) version 2 + + +Introduction +============ + +CAIF is a MUX protocol used by ST-Ericsson cellular modems for +communication between Modem and host. The host processes can open virtual AT +channels, initiate GPRS Data connections, Video channels and Utility Channels. +The Utility Channels are general purpose pipes between modem and host. + +ST-Ericsson modems support a number of transports between modem +and host. Currently, UART and Loopback are available for Linux. + + +Architecture +============ + +The implementation of CAIF is divided into: + +* CAIF Socket Layer and GPRS IP Interface. +* CAIF Core Protocol Implementation +* CAIF Link Layer, implemented as NET devices. + +:: + + RTNL + ! + ! +------+ +------+ + ! +------+! +------+! + ! ! IP !! !Socket!! + +-------> !interf!+ ! API !+ <- CAIF Client APIs + ! +------+ +------! + ! ! ! + ! +-----------+ + ! ! + ! +------+ <- CAIF Core Protocol + ! ! CAIF ! + ! ! Core ! + ! +------+ + ! +----------!---------+ + ! ! ! ! + ! +------+ +-----+ +------+ + +--> ! HSI ! ! TTY ! ! USB ! <- Link Layer (Net Devices) + +------+ +-----+ +------+ + + + +Implementation +============== + + +CAIF Core Protocol Layer +------------------------ + +CAIF Core layer implements the CAIF protocol as defined by ST-Ericsson. +It implements the CAIF protocol stack in a layered approach, where +each layer described in the specification is implemented as a separate layer. +The architecture is inspired by the design patterns "Protocol Layer" and +"Protocol Packet". + +CAIF structure +^^^^^^^^^^^^^^ + +The Core CAIF implementation contains: + + - Simple implementation of CAIF. + - Layered architecture (a la Streams), each layer in the CAIF + specification is implemented in a separate c-file. + - Clients must call configuration function to add PHY layer. + - Clients must implement CAIF layer to consume/produce + CAIF payload with receive and transmit functions. + - Clients must call configuration function to add and connect the + Client layer. + - When receiving / transmitting CAIF Packets (cfpkt), ownership is passed + to the called function (except for framing layers' receive function) + +Layered Architecture +==================== + +The CAIF protocol can be divided into two parts: Support functions and Protocol +Implementation. The support functions include: + + - CFPKT CAIF Packet. Implementation of CAIF Protocol Packet. The + CAIF Packet has functions for creating, destroying and adding content + and for adding/extracting header and trailers to protocol packets. + +The CAIF Protocol implementation contains: + + - CFCNFG CAIF Configuration layer. Configures the CAIF Protocol + Stack and provides a Client interface for adding Link-Layer and + Driver interfaces on top of the CAIF Stack. + + - CFCTRL CAIF Control layer. Encodes and Decodes control messages + such as enumeration and channel setup. Also matches request and + response messages. + + - CFSERVL General CAIF Service Layer functionality; handles flow + control and remote shutdown requests. + + - CFVEI CAIF VEI layer. Handles CAIF AT Channels on VEI (Virtual + External Interface). This layer encodes/decodes VEI frames. + + - CFDGML CAIF Datagram layer. Handles CAIF Datagram layer (IP + traffic), encodes/decodes Datagram frames. + + - CFMUX CAIF Mux layer. Handles multiplexing between multiple + physical bearers and multiple channels such as VEI, Datagram, etc. + The MUX keeps track of the existing CAIF Channels and + Physical Instances and selects the appropriate instance based + on Channel-Id and Physical-ID. + + - CFFRML CAIF Framing layer. Handles Framing i.e. Frame length + and frame checksum. + + - CFSERL CAIF Serial layer. Handles concatenation/split of frames + into CAIF Frames with correct length. + +:: + + +---------+ + | Config | + | CFCNFG | + +---------+ + ! + +---------+ +---------+ +---------+ + | AT | | Control | | Datagram| + | CFVEIL | | CFCTRL | | CFDGML | + +---------+ +---------+ +---------+ + \_____________!______________/ + ! + +---------+ + | MUX | + | | + +---------+ + _____!_____ + / \ + +---------+ +---------+ + | CFFRML | | CFFRML | + | Framing | | Framing | + +---------+ +---------+ + ! ! + +---------+ +---------+ + | | | Serial | + | | | CFSERL | + +---------+ +---------+ + + +In this layered approach the following "rules" apply. + + - All layers embed the same structure "struct cflayer" + - A layer does not depend on any other layer's private data. + - Layers are stacked by setting the pointers:: + + layer->up , layer->dn + + - In order to send data upwards, each layer should do:: + + layer->up->receive(layer->up, packet); + + - In order to send data downwards, each layer should do:: + + layer->dn->transmit(layer->dn, packet); + + +CAIF Socket and IP interface +============================ + +The IP interface and CAIF socket API are implemented on top of the +CAIF Core protocol. The IP Interface and CAIF socket have an instance of +'struct cflayer', just like the CAIF Core protocol stack. +Net device and Socket implement the 'receive()' function defined by +'struct cflayer', just like the rest of the CAIF stack. In this way, transmit and +receive of packets is handled as by the rest of the layers: the 'dn->transmit()' +function is called in order to transmit data. + +Configuration of Link Layer +--------------------------- +The Link Layer is implemented as Linux network devices (struct net_device). +Payload handling and registration is done using standard Linux mechanisms. + +The CAIF Protocol relies on a loss-less link layer without implementing +retransmission. This implies that packet drops must not happen. +Therefore a flow-control mechanism is implemented where the physical +interface can initiate flow stop for all CAIF Channels. |