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+Kernel CAPI Interface to Hardware Drivers
+1. Overview
+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.
+2. Driver and Device Registration
+CAPI drivers optionally register themselves with Kernel CAPI by calling the
+Kernel CAPI function register_capi_driver() with a pointer to a struct
+capi_driver. This structure must be filled with the name and revision of the
+driver, and optionally a pointer to a callback function, add_card(). The
+registration can be revoked by calling the function unregister_capi_driver()
+with a pointer to the same struct capi_driver.
+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
+If the device becomes unusable for any reason (shutdown, disconnect ...), the
+driver has to call capi_ctr_reseted(). 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. The CAPI message to send is stored in the
+data portion of a skb. 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.
+Format and semantics of CAPI messages are specified in the CAPI 2.0 standard.
+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
+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
+int (*add_card)(struct capi_driver *driver, capicardparams *data)
+ a callback function pointer (may be NULL)
+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
+void (*reset_ctr)(struct capi_ctr *ctrlr)
+ pointer to a callback function for performing a reset on the device,
+ releasing all registered applications
+void (*register_appl)(struct capi_ctr *ctrlr, u16 applid,
+ capi_register_params *rparam)
+void (*release_appl)(struct capi_ctr *ctrlr, u16 applid)
+ pointers to callback functions for registration and deregistration of
+ applications with the device
+u16 (*send_message)(struct capi_ctr *ctrlr, struct sk_buff *skb)
+ pointer to a callback function for sending a CAPI message to the
+ device
+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
+read_proc_t *ctr_read_proc
+ pointer to the read_proc callback function for the device's proc file
+ system entry, /proc/capi/controllers/<n>; will be called with a
+ pointer to the device's capi_ctr structure as the last (data) argument
+- to be filled in before calling capi_ctr_ready():
+ 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
+5. Lower Layer Interface Functions
+(declared in <linux/isdn/capilli.h>)
+void register_capi_driver(struct capi_driver *drvr)
+void unregister_capi_driver(struct capi_driver *drvr)
+ register/unregister a driver with Kernel CAPI
+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_reseted(struct capi_ctr *ctrlr)
+ signal controller ready/not ready
+void capi_ctr_suspend_output(struct capi_ctr *ctrlr)
+void capi_ctr_resume_output(struct capi_ctr *ctrlr)
+ signal suspend/resume
+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
+Library functions (from <linux/isdn/capilli.h>):
+void capilib_new_ncci(struct list_head *head, u16 applid,
+ u32 ncci, u32 winsize)
+void capilib_free_ncci(struct list_head *head, u16 applid, u32 ncci)
+void capilib_release_appl(struct list_head *head, u16 applid)
+void capilib_release(struct list_head *head)
+void capilib_data_b3_conf(struct list_head *head, u16 applid,
+ u32 ncci, u16 msgid)
+u16 capilib_data_b3_req(struct list_head *head, u16 applid,
+ u32 ncci, u16 msgid)
+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_CMD(m) - Command*256
+ + Subcommand (u16)
+CAPIMSG_MSGID(m) CAPIMSG_SETMSGID(m, msgid) Message Number (u16)
+ (u32)

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