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diff --git a/Documentation/isdn/credits.rst b/Documentation/isdn/credits.rst
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+=======
+Credits
+=======
+
+
+I want to thank all who contributed to this project and especially to:
+(in alphabetical order)
+
+Thomas Bogendörfer (tsbogend@bigbug.franken.de)
+  Tester, lots of bugfixes and hints.
+
+Alan Cox (alan@lxorguk.ukuu.org.uk)
+  For help getting into standard-kernel.
+
+Henner Eisen (eis@baty.hanse.de)
+  For X.25 implementation.
+
+Volker Götz (volker@oops.franken.de)
+  For contribution of man-pages, the imontty-tool and a perfect
+  maintaining of the mailing-list at hub-wue.
+
+Matthias Hessler (hessler@isdn4linux.de)
+  For creating and maintaining the FAQ.
+
+Bernhard Hailer (Bernhard.Hailer@lrz.uni-muenchen.de)
+  For creating the FAQ, and the leafsite HOWTO.
+
+Michael 'Ghandi' Herold (michael@abadonna.franken.de)
+  For contribution of the vbox answering machine.
+
+Michael Hipp (Michael.Hipp@student.uni-tuebingen.de)
+  For his Sync-PPP-code.
+
+Karsten Keil (keil@isdn4linux.de)
+  For adding 1TR6-support to the Teles-driver.
+  For the HiSax-driver.
+
+Michael Knigge (knick@cove.han.de)
+  For contributing the imon-tool
+
+Andreas Kool (akool@Kool.f.EUnet.de)
+  For contribution of the isdnlog/isdnrep-tool
+
+Pedro Roque Marques (roque@di.fc.ul.pt)
+  For lot of new ideas and the pcbit driver.
+
+Eberhard Mönkeberg (emoenke@gwdg.de)
+  For testing and help to get into kernel.
+
+Thomas Neumann (tn@ruhr.de)
+  For help with Cisco-SLARP and keepalive
+
+Jan den Ouden (denouden@groovin.xs4all.nl)
+  For contribution of the original teles-driver
+
+Carsten Paeth (calle@calle.in-berlin.de)
+  For the AVM-B1-CAPI2.0 driver
+
+Thomas Pfeiffer (pfeiffer@pds.de)
+  For V.110, extended T.70 and Hylafax extensions in isdn_tty.c
+
+Max Riegel (riegel@max.franken.de)
+  For making the ICN hardware-documentation and test-equipment available.
+
+Armin Schindler (mac@melware.de)
+  For the eicon active card driver.
+
+Gerhard 'Fido' Schneider (fido@wuff.mayn.de)
+  For heavy-duty-beta-testing with his BBS ;)
+
+Thomas Uhl (uhl@think.de)
+  For distributing the cards.
+  For pushing me to work ;-)
diff --git a/Documentation/isdn/index.rst b/Documentation/isdn/index.rst
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+++ b/Documentation/isdn/index.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+====
+ISDN
+====
+
+.. toctree::
+   :maxdepth: 2
+
+   interface_capi
+
+   m_isdn
+
+   credits
+
+.. only::  subproject and html
+
+   Indices
+   =======
+
+   * :ref:`genindex`
diff --git a/Documentation/isdn/interface_capi.rst b/Documentation/isdn/interface_capi.rst
new file mode 100644
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+=========================================
+Kernel CAPI Interface to Hardware Drivers
+=========================================
+
+1. Overview
+===========
+
+From the CAPI 2.0 specification:
+COMMON-ISDN-API (CAPI) is an application programming interface standard used
+to access ISDN equipment connected to basic rate interfaces (BRI) and primary
+rate interfaces (PRI).
+
+Kernel CAPI operates as a dispatching layer between CAPI applications and CAPI
+hardware drivers. Hardware drivers register ISDN devices (controllers, in CAPI
+lingo) with Kernel CAPI to indicate their readiness to provide their service
+to CAPI applications. CAPI applications also register with Kernel CAPI,
+requesting association with a CAPI device. Kernel CAPI then dispatches the
+application registration to an available device, forwarding it to the
+corresponding hardware driver. Kernel CAPI then forwards CAPI messages in both
+directions between the application and the hardware driver.
+
+Format and semantics of CAPI messages are specified in the CAPI 2.0 standard.
+This standard is freely available from https://www.capi.org.
+
+
+2. Driver and Device Registration
+=================================
+
+CAPI drivers must register each of the ISDN devices they control with Kernel
+CAPI by calling the Kernel CAPI function attach_capi_ctr() with a pointer to a
+struct capi_ctr before they can be used. This structure must be filled with
+the names of the driver and controller, and a number of callback function
+pointers which are subsequently used by Kernel CAPI for communicating with the
+driver. The registration can be revoked by calling the function
+detach_capi_ctr() with a pointer to the same struct capi_ctr.
+
+Before the device can be actually used, the driver must fill in the device
+information fields 'manu', 'version', 'profile' and 'serial' in the capi_ctr
+structure of the device, and signal its readiness by calling capi_ctr_ready().
+From then on, Kernel CAPI may call the registered callback functions for the
+device.
+
+If the device becomes unusable for any reason (shutdown, disconnect ...), the
+driver has to call capi_ctr_down(). This will prevent further calls to the
+callback functions by Kernel CAPI.
+
+
+3. Application Registration and Communication
+=============================================
+
+Kernel CAPI forwards registration requests from applications (calls to CAPI
+operation CAPI_REGISTER) to an appropriate hardware driver by calling its
+register_appl() callback function. A unique Application ID (ApplID, u16) is
+allocated by Kernel CAPI and passed to register_appl() along with the
+parameter structure provided by the application. This is analogous to the
+open() operation on regular files or character devices.
+
+After a successful return from register_appl(), CAPI messages from the
+application may be passed to the driver for the device via calls to the
+send_message() callback function. Conversely, the driver may call Kernel
+CAPI's capi_ctr_handle_message() function to pass a received CAPI message to
+Kernel CAPI for forwarding to an application, specifying its ApplID.
+
+Deregistration requests (CAPI operation CAPI_RELEASE) from applications are
+forwarded as calls to the release_appl() callback function, passing the same
+ApplID as with register_appl(). After return from release_appl(), no CAPI
+messages for that application may be passed to or from the device anymore.
+
+
+4. Data Structures
+==================
+
+4.1 struct capi_driver
+----------------------
+
+This structure describes a Kernel CAPI driver itself. It is used in the
+register_capi_driver() and unregister_capi_driver() functions, and contains
+the following non-private fields, all to be set by the driver before calling
+register_capi_driver():
+
+``char name[32]``
+	the name of the driver, as a zero-terminated ASCII string
+``char revision[32]``
+	the revision number of the driver, as a zero-terminated ASCII string
+
+4.2 struct capi_ctr
+-------------------
+
+This structure describes an ISDN device (controller) handled by a Kernel CAPI
+driver. After registration via the attach_capi_ctr() function it is passed to
+all controller specific lower layer interface and callback functions to
+identify the controller to operate on.
+
+It contains the following non-private fields:
+
+to be set by the driver before calling attach_capi_ctr():
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``struct module *owner``
+	pointer to the driver module owning the device
+
+``void *driverdata``
+	an opaque pointer to driver specific data, not touched by Kernel CAPI
+
+``char name[32]``
+	the name of the controller, as a zero-terminated ASCII string
+
+``char *driver_name``
+	the name of the driver, as a zero-terminated ASCII string
+
+``int (*load_firmware)(struct capi_ctr *ctrlr, capiloaddata *ldata)``
+	(optional) pointer to a callback function for sending firmware and
+	configuration data to the device
+
+	The function may return before the operation has completed.
+
+	Completion must be signalled by a call to capi_ctr_ready().
+
+	Return value: 0 on success, error code on error
+	Called in process context.
+
+``void (*reset_ctr)(struct capi_ctr *ctrlr)``
+	(optional) pointer to a callback function for stopping the device,
+	releasing all registered applications
+
+	The function may return before the operation has completed.
+
+	Completion must be signalled by a call to capi_ctr_down().
+
+	Called in process context.
+
+``void (*register_appl)(struct capi_ctr *ctrlr, u16 applid, capi_register_params *rparam)``
+	pointers to callback function for registration of
+	applications with the device
+
+	Calls to these functions are serialized by Kernel CAPI so that only
+	one call to any of them is active at any time.
+
+``void (*release_appl)(struct capi_ctr *ctrlr, u16 applid)``
+	pointers to callback functions deregistration of
+	applications with the device
+
+	Calls to these functions are serialized by Kernel CAPI so that only
+	one call to any of them is active at any time.
+
+``u16  (*send_message)(struct capi_ctr *ctrlr, struct sk_buff *skb)``
+	pointer to a callback function for sending a CAPI message to the
+	device
+
+	Return value: CAPI error code
+
+	If the method returns 0 (CAPI_NOERROR) the driver has taken ownership
+	of the skb and the caller may no longer access it. If it returns a
+	non-zero (error) value then ownership of the skb returns to the caller
+	who may reuse or free it.
+
+	The return value should only be used to signal problems with respect
+	to accepting or queueing the message. Errors occurring during the
+	actual processing of the message should be signaled with an
+	appropriate reply message.
+
+	May be called in process or interrupt context.
+
+	Calls to this function are not serialized by Kernel CAPI, ie. it must
+	be prepared to be re-entered.
+
+``char *(*procinfo)(struct capi_ctr *ctrlr)``
+	pointer to a callback function returning the entry for the device in
+	the CAPI controller info table, /proc/capi/controller
+
+Note:
+  Callback functions except send_message() are never called in interrupt
+  context.
+
+to be filled in before calling capi_ctr_ready():
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``u8 manu[CAPI_MANUFACTURER_LEN]``
+	value to return for CAPI_GET_MANUFACTURER
+
+``capi_version version``
+	value to return for CAPI_GET_VERSION
+
+``capi_profile profile``
+	value to return for CAPI_GET_PROFILE
+
+``u8 serial[CAPI_SERIAL_LEN]``
+	value to return for CAPI_GET_SERIAL
+
+
+4.3 SKBs
+--------
+
+CAPI messages are passed between Kernel CAPI and the driver via send_message()
+and capi_ctr_handle_message(), stored in the data portion of a socket buffer
+(skb).  Each skb contains a single CAPI message coded according to the CAPI 2.0
+standard.
+
+For the data transfer messages, DATA_B3_REQ and DATA_B3_IND, the actual
+payload data immediately follows the CAPI message itself within the same skb.
+The Data and Data64 parameters are not used for processing. The Data64
+parameter may be omitted by setting the length field of the CAPI message to 22
+instead of 30.
+
+
+4.4 The _cmsg Structure
+-----------------------
+
+(declared in <linux/isdn/capiutil.h>)
+
+The _cmsg structure stores the contents of a CAPI 2.0 message in an easily
+accessible form. It contains members for all possible CAPI 2.0 parameters,
+including subparameters of the Additional Info and B Protocol structured
+parameters, with the following exceptions:
+
+* second Calling party number (CONNECT_IND)
+
+* Data64 (DATA_B3_REQ and DATA_B3_IND)
+
+* Sending complete (subparameter of Additional Info, CONNECT_REQ and INFO_REQ)
+
+* Global Configuration (subparameter of B Protocol, CONNECT_REQ, CONNECT_RESP
+  and SELECT_B_PROTOCOL_REQ)
+
+Only those parameters appearing in the message type currently being processed
+are actually used. Unused members should be set to zero.
+
+Members are named after the CAPI 2.0 standard names of the parameters they
+represent. See <linux/isdn/capiutil.h> for the exact spelling. Member data
+types are:
+
+=========== =================================================================
+u8          for CAPI parameters of type 'byte'
+
+u16         for CAPI parameters of type 'word'
+
+u32         for CAPI parameters of type 'dword'
+
+_cstruct    for CAPI parameters of type 'struct'
+	    The member is a pointer to a buffer containing the parameter in
+	    CAPI encoding (length + content). It may also be NULL, which will
+	    be taken to represent an empty (zero length) parameter.
+	    Subparameters are stored in encoded form within the content part.
+
+_cmstruct   alternative representation for CAPI parameters of type 'struct'
+	    (used only for the 'Additional Info' and 'B Protocol' parameters)
+	    The representation is a single byte containing one of the values:
+	    CAPI_DEFAULT: The parameter is empty/absent.
+	    CAPI_COMPOSE: The parameter is present.
+	    Subparameter values are stored individually in the corresponding
+	    _cmsg structure members.
+=========== =================================================================
+
+
+5. Lower Layer Interface Functions
+==================================
+
+::
+
+  int attach_capi_ctr(struct capi_ctr *ctrlr)
+  int detach_capi_ctr(struct capi_ctr *ctrlr)
+
+register/unregister a device (controller) with Kernel CAPI
+
+::
+
+  void capi_ctr_ready(struct capi_ctr *ctrlr)
+  void capi_ctr_down(struct capi_ctr *ctrlr)
+
+signal controller ready/not ready
+
+::
+
+  void capi_ctr_handle_message(struct capi_ctr * ctrlr, u16 applid,
+			       struct sk_buff *skb)
+
+pass a received CAPI message to Kernel CAPI
+for forwarding to the specified application
+
+
+6. Helper Functions and Macros
+==============================
+
+Macros to extract/set element values from/in a CAPI message header
+(from <linux/isdn/capiutil.h>):
+
+======================  =============================   ====================
+Get Macro		Set Macro			Element (Type)
+======================  =============================   ====================
+CAPIMSG_LEN(m)		CAPIMSG_SETLEN(m, len)		Total Length (u16)
+CAPIMSG_APPID(m)	CAPIMSG_SETAPPID(m, applid)	ApplID (u16)
+CAPIMSG_COMMAND(m)	CAPIMSG_SETCOMMAND(m,cmd)	Command (u8)
+CAPIMSG_SUBCOMMAND(m)	CAPIMSG_SETSUBCOMMAND(m, cmd)	Subcommand (u8)
+CAPIMSG_CMD(m)		-				Command*256
+							+ Subcommand (u16)
+CAPIMSG_MSGID(m)	CAPIMSG_SETMSGID(m, msgid)	Message Number (u16)
+
+CAPIMSG_CONTROL(m)	CAPIMSG_SETCONTROL(m, contr)	Controller/PLCI/NCCI
+							(u32)
+CAPIMSG_DATALEN(m)	CAPIMSG_SETDATALEN(m, len)	Data Length (u16)
+======================  =============================   ====================
+
+
+Library functions for working with _cmsg structures
+(from <linux/isdn/capiutil.h>):
+
+``char *capi_cmd2str(u8 Command, u8 Subcommand)``
+	Returns the CAPI 2.0 message name corresponding to the given command
+	and subcommand values, as a static ASCII string. The return value may
+	be NULL if the command/subcommand is not one of those defined in the
+	CAPI 2.0 standard.
+
+
+7. Debugging
+============
+
+The module kernelcapi has a module parameter showcapimsgs controlling some
+debugging output produced by the module. It can only be set when the module is
+loaded, via a parameter "showcapimsgs=<n>" to the modprobe command, either on
+the command line or in the configuration file.
+
+If the lowest bit of showcapimsgs is set, kernelcapi logs controller and
+application up and down events.
+
+In addition, every registered CAPI controller has an associated traceflag
+parameter controlling how CAPI messages sent from and to tha controller are
+logged. The traceflag parameter is initialized with the value of the
+showcapimsgs parameter when the controller is registered, but can later be
+changed via the MANUFACTURER_REQ command KCAPI_CMD_TRACE.
+
+If the value of traceflag is non-zero, CAPI messages are logged.
+DATA_B3 messages are only logged if the value of traceflag is > 2.
+
+If the lowest bit of traceflag is set, only the command/subcommand and message
+length are logged. Otherwise, kernelcapi logs a readable representation of
+the entire message.
diff --git a/Documentation/isdn/m_isdn.rst b/Documentation/isdn/m_isdn.rst
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+============
+mISDN Driver
+============
+
+mISDN is a new modular ISDN driver, in the long term it should replace
+the old I4L driver architecture for passiv ISDN cards.
+It was designed to allow a broad range of applications and interfaces
+but only have the basic function in kernel, the interface to the user
+space is based on sockets with a own address family AF_ISDN.