Adding upstream version 6.1.76.upstream/6.1.76

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

1 files changed, 195 insertions, 0 deletions

diff --git a/Documentation/networking/caif/linux_caif.rst b/Documentation/networking/caif/linux_caif.rst
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+.. 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.