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Date: Wed, 20 Jan 2010 23:55:29 +0100
From: sjur.brandeland@...ricsson.com
To: netdev@...r.kernel.org
Cc: davem@...emloft.net, marcel@...tmann.org,
stefano.babic@...ic.homelinux.org, randy.dunlap@...cle.com,
Sjur Braendeland <sjur.brandeland@...ricsson.com>
Subject: [PATCH net-next-2.6 12/13] net-caif: add CAIF documentation
From: Sjur Braendeland <sjur.brandeland@...ricsson.com>
Documentation of the CAIF Protocol.
Signed-off-by: Sjur Braendeland <sjur.brandeland@...ricsson.com>
---
Documentation/networking/caif/Linux-CAIF.txt | 235 ++++++++++++++++++++++++++
Documentation/networking/caif/README | 27 +++
2 files changed, 262 insertions(+), 0 deletions(-)
diff --git a/Documentation/networking/caif/Linux-CAIF.txt b/Documentation/networking/caif/Linux-CAIF.txt
new file mode 100644
index 0000000..5576e42
--- /dev/null
+++ b/Documentation/networking/caif/Linux-CAIF.txt
@@ -0,0 +1,235 @@
+Linux CAIF
+===========
+copyright (C) ST-Ericsson AB 2010
+Author: Sjur Brendeland/ sjur.brandeland@...ricsson.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, Kernel API, and Net Device.
+* CAIF Generic Protocol Implementation
+* CAIF Link Layer, implemented as NET devices.
+
+
+ RTNL/IOCTL
+ !
+ ! +------+ +------+ +------+
+ ! +------+! +------+! +------+!
+ ! ! Sock !! !Kernel!! ! Net !!
+ ! ! API !+ ! API !+ ! Dev !+ <- CAIF Client APIs
+ ! +------+ +------! +------+
+ ! ! ! !
+ ! +----------!----------+
+ ! +------+ <- CAIF Protocol Implementation
+ +-------> ! CAIF !
+ +------+
+ +--------!--------+
+ ! !
+ +------+ +-----+
+ !Loop ! ! TTY ! <- Link Layer (Net Devices)
+ +------+ +-----+
+
+
+Using CAIF (IP) Net Device
+----------------------
+CAIF Net device can be created by use of Socket IOCTLs,
+or RT Netlink.
+
+ static struct ifcaif_param param = {
+ .ipv4_connid = 1,
+ .loop = 0
+ };
+ static struct ifreq ifr = {
+ .ifr_name = "caif%d",
+ .ifr_ifru.ifru_data = ¶m
+
+ };
+ s = socket(AF_CAIF, SOCK_SEQPACKET, CAIFPROTO_AT);
+ ioctl(s, SIOCCAIFNETNEW, &ifr);
+
+
+Using the Kernel API
+----------------------
+The Kernel API is used for accessing CAIF channels from the
+kernel.
+The user of the API has to implement two callbacks for receive
+and control.
+The receive callback gives a CAIF packet as a SKB. The control
+callback will
+notify of channel initialization complete, and flow-on/flow-
+off.
+
+
+ struct caif_device caif_dev = {
+ .caif_config = {
+ .name = "MYDEV"
+ .type = CAIF_CHTY_AT
+ }
+ .receive_cb = my_receive,
+ .control_cb = my_control,
+ };
+ caif_add_device(&caif_dev);
+ caif_transmit(&caif_dev, skb);
+
+See the caif_kernel.h for details about the CAIF kernel API.
+
+
+I M P L E M E N T A T I O N
+===========================
+===========================
+
+Generic CAIF Protocol Layer
+=========================================
+
+caif/generic is a generic CAIF protocol implementation. It 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 goal is to have generic CAIF as OS and system independent as possible.
+All generic CAIF code can be found under net/caif/generic and
+include/net/caif/generic.
+
+The generic CAIF implementation is:
+ - Simple implementation of CAIF.
+ - Layered architecture (a la Streams), each layer in the CAIF
+ specification is implemented in a separate c-file.
+ - Clients must implement PHY layer to access physical HW
+ with receive and transmit functions.
+ - Clients must call configuration function to add PHY layer.
+ - Clients must implement adaptation layer to consume/produce
+ CAIF payload with receive and transmit functions.
+ - Clients must call configuration function to add adaptation
+ layer.
+ - When receiving / transmitting CAIF Packets (cfpkt), ownership is passed
+ to the called function (except for framing layers' receive functions
+ or if a transmit function returns an error, in which case the caller
+ must free the packet).
+
+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.
+
+ - CFLST CAIF list implementation.
+
+ - CFGLUE CAIF Glue. Contains OS Specifics, such as memory
+ allocation, endianness, etc.
+
+The CAIF Protocol implementation contains:
+
+ - CFCNFG CAIF Configuration layer. Configures the CAIF Protocol
+ Stack and has 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 VEI layer (AT-Channel),
+ encodes/decodes VEI frames.
+
+ - CFDGML CAIF Data-gram layer. Handles CAIF Data-gram 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 apropriate 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" applies.
+ - All layers embedd the same structure "struct layer"
+ - 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);
+
+
+Linux Driver Implementation
+===========================
+
+Linux GPRS Net Device and CAIF socket are implemented on top of the
+Generic CAIF protocol. The Net device and CAIF socket have an instance of
+'struct layer', just like the generic CAIF protocol stack.
+Net device and Socket implement the 'receive()' function defined by
+'struct layer', 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.
+
+The layer on top of the generic CAIF implementation is
+sometimes refered to as the "adaptation layer".
+
+
+Configuration of Link Layer
+---------------------------
+The Link Layer is implemented as Linux net devices (struct net_device).
+Payload handling and registration is done using standard Linux mecanisms.
+
+The CAIF Protocol relies on a lossless link layer without implementing
+retransmission. This implies that packet drops must not happen.
+Therefor a flow-control mecanism is implemented where the physical
+interface can initiate flow stop for all CAIF Channels.
diff --git a/Documentation/networking/caif/README b/Documentation/networking/caif/README
new file mode 100644
index 0000000..b3b4694
--- /dev/null
+++ b/Documentation/networking/caif/README
@@ -0,0 +1,27 @@
+copyright (C) ST-Ericsson AB 2010
+Author: Sjur Brendeland/ sjur.brandeland@...ricsson.com
+License terms: GNU General Public License (GPL) version 2
+
+=== Start ===
+If you have compiled CAIF for modules do:
+
+$modprobe caif
+$modprobe caif_socket
+$modprobe chnl_net
+
+
+=== Preparing the setup with a STE modem ===
+
+Make sure that the kernel is built with module support.
+
+There are some things that need to be tweaked to get the host TTY
+correctly set up to talk to the modem.
+Since the CAIF stack is running in the kernel and we want to use the existing
+TTY, we are installing our physical serial driver as a line discipline above
+the TTY device. The TTY device used to communicate to modem must be specified
+as a module parameter to caif_serial (ser_ttyname=<name>).
+The use of Start-of-frame-extension (STX) must also be set as
+module parameter, if not the parameter must be set to "no".
+
+$ modprobe caif_serial ser_ttyname=/dev/ttyS0 ser_use_stx=yes
+$ ifconfig caifser0 up
--
1.6.3.3
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