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1=========================================2Kernel CAPI Interface to Hardware Drivers3=========================================4 51. Overview6===========7 8From the CAPI 2.0 specification:9COMMON-ISDN-API (CAPI) is an application programming interface standard used10to access ISDN equipment connected to basic rate interfaces (BRI) and primary11rate interfaces (PRI).12 13Kernel CAPI operates as a dispatching layer between CAPI applications and CAPI14hardware drivers. Hardware drivers register ISDN devices (controllers, in CAPI15lingo) with Kernel CAPI to indicate their readiness to provide their service16to CAPI applications. CAPI applications also register with Kernel CAPI,17requesting association with a CAPI device. Kernel CAPI then dispatches the18application registration to an available device, forwarding it to the19corresponding hardware driver. Kernel CAPI then forwards CAPI messages in both20directions between the application and the hardware driver.21 22Format and semantics of CAPI messages are specified in the CAPI 2.0 standard.23This standard is freely available from https://www.capi.org.24 25 262. Driver and Device Registration27=================================28 29CAPI drivers must register each of the ISDN devices they control with Kernel30CAPI by calling the Kernel CAPI function attach_capi_ctr() with a pointer to a31struct capi_ctr before they can be used. This structure must be filled with32the names of the driver and controller, and a number of callback function33pointers which are subsequently used by Kernel CAPI for communicating with the34driver. The registration can be revoked by calling the function35detach_capi_ctr() with a pointer to the same struct capi_ctr.36 37Before the device can be actually used, the driver must fill in the device38information fields 'manu', 'version', 'profile' and 'serial' in the capi_ctr39structure of the device, and signal its readiness by calling capi_ctr_ready().40From then on, Kernel CAPI may call the registered callback functions for the41device.42 43If the device becomes unusable for any reason (shutdown, disconnect ...), the44driver has to call capi_ctr_down(). This will prevent further calls to the45callback functions by Kernel CAPI.46 47 483. Application Registration and Communication49=============================================50 51Kernel CAPI forwards registration requests from applications (calls to CAPI52operation CAPI_REGISTER) to an appropriate hardware driver by calling its53register_appl() callback function. A unique Application ID (ApplID, u16) is54allocated by Kernel CAPI and passed to register_appl() along with the55parameter structure provided by the application. This is analogous to the56open() operation on regular files or character devices.57 58After a successful return from register_appl(), CAPI messages from the59application may be passed to the driver for the device via calls to the60send_message() callback function. Conversely, the driver may call Kernel61CAPI's capi_ctr_handle_message() function to pass a received CAPI message to62Kernel CAPI for forwarding to an application, specifying its ApplID.63 64Deregistration requests (CAPI operation CAPI_RELEASE) from applications are65forwarded as calls to the release_appl() callback function, passing the same66ApplID as with register_appl(). After return from release_appl(), no CAPI67messages for that application may be passed to or from the device anymore.68 69 704. Data Structures71==================72 734.1 struct capi_driver74----------------------75 76This structure describes a Kernel CAPI driver itself. It is used in the77register_capi_driver() and unregister_capi_driver() functions, and contains78the following non-private fields, all to be set by the driver before calling79register_capi_driver():80 81``char name[32]``82 the name of the driver, as a zero-terminated ASCII string83``char revision[32]``84 the revision number of the driver, as a zero-terminated ASCII string85 864.2 struct capi_ctr87-------------------88 89This structure describes an ISDN device (controller) handled by a Kernel CAPI90driver. After registration via the attach_capi_ctr() function it is passed to91all controller specific lower layer interface and callback functions to92identify the controller to operate on.93 94It contains the following non-private fields:95 96to be set by the driver before calling attach_capi_ctr():97^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^98 99``struct module *owner``100 pointer to the driver module owning the device101 102``void *driverdata``103 an opaque pointer to driver specific data, not touched by Kernel CAPI104 105``char name[32]``106 the name of the controller, as a zero-terminated ASCII string107 108``char *driver_name``109 the name of the driver, as a zero-terminated ASCII string110 111``int (*load_firmware)(struct capi_ctr *ctrlr, capiloaddata *ldata)``112 (optional) pointer to a callback function for sending firmware and113 configuration data to the device114 115 The function may return before the operation has completed.116 117 Completion must be signalled by a call to capi_ctr_ready().118 119 Return value: 0 on success, error code on error120 Called in process context.121 122``void (*reset_ctr)(struct capi_ctr *ctrlr)``123 (optional) pointer to a callback function for stopping the device,124 releasing all registered applications125 126 The function may return before the operation has completed.127 128 Completion must be signalled by a call to capi_ctr_down().129 130 Called in process context.131 132``void (*register_appl)(struct capi_ctr *ctrlr, u16 applid, capi_register_params *rparam)``133 pointers to callback function for registration of134 applications with the device135 136 Calls to these functions are serialized by Kernel CAPI so that only137 one call to any of them is active at any time.138 139``void (*release_appl)(struct capi_ctr *ctrlr, u16 applid)``140 pointers to callback functions deregistration of141 applications with the device142 143 Calls to these functions are serialized by Kernel CAPI so that only144 one call to any of them is active at any time.145 146``u16 (*send_message)(struct capi_ctr *ctrlr, struct sk_buff *skb)``147 pointer to a callback function for sending a CAPI message to the148 device149 150 Return value: CAPI error code151 152 If the method returns 0 (CAPI_NOERROR) the driver has taken ownership153 of the skb and the caller may no longer access it. If it returns a154 non-zero (error) value then ownership of the skb returns to the caller155 who may reuse or free it.156 157 The return value should only be used to signal problems with respect158 to accepting or queueing the message. Errors occurring during the159 actual processing of the message should be signaled with an160 appropriate reply message.161 162 May be called in process or interrupt context.163 164 Calls to this function are not serialized by Kernel CAPI, ie. it must165 be prepared to be re-entered.166 167``char *(*procinfo)(struct capi_ctr *ctrlr)``168 pointer to a callback function returning the entry for the device in169 the CAPI controller info table, /proc/capi/controller170 171Note:172 Callback functions except send_message() are never called in interrupt173 context.174 175to be filled in before calling capi_ctr_ready():176^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^177 178``u8 manu[CAPI_MANUFACTURER_LEN]``179 value to return for CAPI_GET_MANUFACTURER180 181``capi_version version``182 value to return for CAPI_GET_VERSION183 184``capi_profile profile``185 value to return for CAPI_GET_PROFILE186 187``u8 serial[CAPI_SERIAL_LEN]``188 value to return for CAPI_GET_SERIAL189 190 1914.3 SKBs192--------193 194CAPI messages are passed between Kernel CAPI and the driver via send_message()195and capi_ctr_handle_message(), stored in the data portion of a socket buffer196(skb). Each skb contains a single CAPI message coded according to the CAPI 2.0197standard.198 199For the data transfer messages, DATA_B3_REQ and DATA_B3_IND, the actual200payload data immediately follows the CAPI message itself within the same skb.201The Data and Data64 parameters are not used for processing. The Data64202parameter may be omitted by setting the length field of the CAPI message to 22203instead of 30.204 205 2064.4 The _cmsg Structure207-----------------------208 209(declared in <linux/isdn/capiutil.h>)210 211The _cmsg structure stores the contents of a CAPI 2.0 message in an easily212accessible form. It contains members for all possible CAPI 2.0 parameters,213including subparameters of the Additional Info and B Protocol structured214parameters, with the following exceptions:215 216* second Calling party number (CONNECT_IND)217 218* Data64 (DATA_B3_REQ and DATA_B3_IND)219 220* Sending complete (subparameter of Additional Info, CONNECT_REQ and INFO_REQ)221 222* Global Configuration (subparameter of B Protocol, CONNECT_REQ, CONNECT_RESP223 and SELECT_B_PROTOCOL_REQ)224 225Only those parameters appearing in the message type currently being processed226are actually used. Unused members should be set to zero.227 228Members are named after the CAPI 2.0 standard names of the parameters they229represent. See <linux/isdn/capiutil.h> for the exact spelling. Member data230types are:231 232=========== =================================================================233u8 for CAPI parameters of type 'byte'234 235u16 for CAPI parameters of type 'word'236 237u32 for CAPI parameters of type 'dword'238 239_cstruct for CAPI parameters of type 'struct'240 The member is a pointer to a buffer containing the parameter in241 CAPI encoding (length + content). It may also be NULL, which will242 be taken to represent an empty (zero length) parameter.243 Subparameters are stored in encoded form within the content part.244 245_cmstruct alternative representation for CAPI parameters of type 'struct'246 (used only for the 'Additional Info' and 'B Protocol' parameters)247 The representation is a single byte containing one of the values:248 CAPI_DEFAULT: The parameter is empty/absent.249 CAPI_COMPOSE: The parameter is present.250 Subparameter values are stored individually in the corresponding251 _cmsg structure members.252=========== =================================================================253 254 2555. Lower Layer Interface Functions256==================================257 258::259 260 int attach_capi_ctr(struct capi_ctr *ctrlr)261 int detach_capi_ctr(struct capi_ctr *ctrlr)262 263register/unregister a device (controller) with Kernel CAPI264 265::266 267 void capi_ctr_ready(struct capi_ctr *ctrlr)268 void capi_ctr_down(struct capi_ctr *ctrlr)269 270signal controller ready/not ready271 272::273 274 void capi_ctr_handle_message(struct capi_ctr * ctrlr, u16 applid,275 struct sk_buff *skb)276 277pass a received CAPI message to Kernel CAPI278for forwarding to the specified application279 280 2816. Helper Functions and Macros282==============================283 284Macros to extract/set element values from/in a CAPI message header285(from <linux/isdn/capiutil.h>):286 287====================== ============================= ====================288Get Macro Set Macro Element (Type)289====================== ============================= ====================290CAPIMSG_LEN(m) CAPIMSG_SETLEN(m, len) Total Length (u16)291CAPIMSG_APPID(m) CAPIMSG_SETAPPID(m, applid) ApplID (u16)292CAPIMSG_COMMAND(m) CAPIMSG_SETCOMMAND(m,cmd) Command (u8)293CAPIMSG_SUBCOMMAND(m) CAPIMSG_SETSUBCOMMAND(m, cmd) Subcommand (u8)294CAPIMSG_CMD(m) - Command*256295 + Subcommand (u16)296CAPIMSG_MSGID(m) CAPIMSG_SETMSGID(m, msgid) Message Number (u16)297 298CAPIMSG_CONTROL(m) CAPIMSG_SETCONTROL(m, contr) Controller/PLCI/NCCI299 (u32)300CAPIMSG_DATALEN(m) CAPIMSG_SETDATALEN(m, len) Data Length (u16)301====================== ============================= ====================302 303 304Library functions for working with _cmsg structures305(from <linux/isdn/capiutil.h>):306 307``char *capi_cmd2str(u8 Command, u8 Subcommand)``308 Returns the CAPI 2.0 message name corresponding to the given command309 and subcommand values, as a static ASCII string. The return value may310 be NULL if the command/subcommand is not one of those defined in the311 CAPI 2.0 standard.312 313 3147. Debugging315============316 317The module kernelcapi has a module parameter showcapimsgs controlling some318debugging output produced by the module. It can only be set when the module is319loaded, via a parameter "showcapimsgs=<n>" to the modprobe command, either on320the command line or in the configuration file.321 322If the lowest bit of showcapimsgs is set, kernelcapi logs controller and323application up and down events.324 325In addition, every registered CAPI controller has an associated traceflag326parameter controlling how CAPI messages sent from and to the controller are327logged. The traceflag parameter is initialized with the value of the328showcapimsgs parameter when the controller is registered, but can later be329changed via the MANUFACTURER_REQ command KCAPI_CMD_TRACE.330 331If the value of traceflag is non-zero, CAPI messages are logged.332DATA_B3 messages are only logged if the value of traceflag is > 2.333 334If the lowest bit of traceflag is set, only the command/subcommand and message335length are logged. Otherwise, kernelcapi logs a readable representation of336the entire message.337