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+S/390 driver model interfaces
+1. CCW devices
+All devices which can be addressed by means of ccws are called 'CCW devices' -
+even if they aren't actually driven by ccws.
+All ccw devices are accessed via a subchannel, this is reflected in the
+structures under root/:
+ - sys
+ - legacy
+ - css0/
+ - 0.0.0000/0.0.0815/
+ - 0.0.0001/0.0.4711/
+ - 0.0.0002/
+ ...
+In this example, device 0815 is accessed via subchannel 0, device 4711 via
+subchannel 1, and subchannel 2 is a non-I/O subchannel.
+You should address a ccw device via its bus id (e.g. 0.0.4711); the device can
+be found under bus/ccw/devices/.
+All ccw devices export some data via sysfs.
+cutype: The control unit type / model.
+devtype: The device type / model, if applicable.
+availability: Can be 'good' or 'boxed'; 'no path' or 'no device' for
+ disconnected devices.
+online: An interface to set the device online and offline.
+ In the special case of the device being disconnected (see the
+ notify function under 1.2), piping 0 to online will focibly delete
+ the device.
+The device drivers can add entries to export per-device data and interfaces.
+There is also some data exported on a per-subchannel basis (see under
+chpids: Via which chpids the device is connected.
+pimpampom: The path installed, path available and path operational masks.
+There also might be additional data, for example for block devices.
+1.1 Bringing up a ccw device
+This is done in several steps.
+a. Each driver can provide one or more parameter interfaces where parameters can
+ be specified. These interfaces are also in the driver's responsibility.
+b. After a. has been performed, if necessary, the device is finally brought up
+ via the 'online' interface.
+1.2 Writing a driver for ccw devices
+The basic struct ccw_device and struct ccw_driver data structures can be found
+under include/asm/ccwdev.h.
+struct ccw_device {
+ spinlock_t *ccwlock;
+ struct ccw_device_private *private;
+ struct ccw_device_id id;
+ struct ccw_driver *drv;
+ struct device dev;
+ int online;
+ void (*handler) (struct ccw_device *dev, unsigned long intparm,
+ struct irb *irb);
+struct ccw_driver {
+ struct module *owner;
+ struct ccw_device_id *ids;
+ int (*probe) (struct ccw_device *);
+ int (*remove) (struct ccw_device *);
+ int (*set_online) (struct ccw_device *);
+ int (*set_offline) (struct ccw_device *);
+ int (*notify) (struct ccw_device *, int);
+ struct device_driver driver;
+ char *name;
+The 'private' field contains data needed for internal i/o operation only, and
+is not available to the device driver.
+Each driver should declare in a MODULE_DEVICE_TABLE into which CU types/models
+and/or device types/models it is interested. This information can later be found
+found in the struct ccw_device_id fields:
+struct ccw_device_id {
+ __u16 match_flags;
+ __u16 cu_type;
+ __u16 dev_type;
+ __u8 cu_model;
+ __u8 dev_model;
+ unsigned long driver_info;
+The functions in ccw_driver should be used in the following way:
+probe: This function is called by the device layer for each device the driver
+ is interested in. The driver should only allocate private structures
+ to put in dev->driver_data and create attributes (if needed). Also,
+ the interrupt handler (see below) should be set here.
+int (*probe) (struct ccw_device *cdev);
+Parameters: cdev - the device to be probed.
+remove: This function is called by the device layer upon removal of the driver,
+ the device or the module. The driver should perform cleanups here.
+int (*remove) (struct ccw_device *cdev);
+Parameters: cdev - the device to be removed.
+set_online: This function is called by the common I/O layer when the device is
+ activated via the 'online' attribute. The driver should finally
+ setup and activate the device here.
+int (*set_online) (struct ccw_device *);
+Parameters: cdev - the device to be activated. The common layer has
+ verified that the device is not already online.
+set_offline: This function is called by the common I/O layer when the device is
+ de-activated via the 'online' attribute. The driver should shut
+ down the device, but not de-allocate its private data.
+int (*set_offline) (struct ccw_device *);
+Parameters: cdev - the device to be deactivated. The common layer has
+ verified that the device is online.
+notify: This function is called by the common I/O layer for some state changes
+ of the device.
+ Signalled to the driver are:
+ * In online state, device detached (CIO_GONE) or last path gone
+ (CIO_NO_PATH). The driver must return !0 to keep the device; for
+ return code 0, the device will be deleted as usual (also when no
+ notify function is registerd). If the driver wants to keep the
+ device, it is moved into disconnected state.
+ * In disconnected state, device operational again (CIO_OPER). The
+ common I/O layer performs some sanity checks on device number and
+ Device / CU to be reasonably sure if it is still the same device.
+ If not, the old device is removed and a new one registered. By the
+ return code of the notify function the device driver signals if it
+ wants the device back: !0 for keeping, 0 to make the device being
+ removed and re-registered.
+int (*notify) (struct ccw_device *, int);
+Parameters: cdev - the device whose state changed.
+ event - the event that happened. This can be one of CIO_GONE,
+The handler field of the struct ccw_device is meant to be set to the interrupt
+handler for the device. In order to accommodate drivers which use several
+distinct handlers (e.g. multi subchannel devices), this is a member of ccw_device
+instead of ccw_driver.
+The handler is registered with the common layer during set_online() processing
+before the driver is called, and is deregistered during set_offline() after the
+driver has been called. Also, after registering / before deregistering, path
+grouping resp. disbanding of the path group (if applicable) are performed.
+void (*handler) (struct ccw_device *dev, unsigned long intparm, struct irb *irb);
+Parameters: dev - the device the handler is called for
+ intparm - the intparm which allows the device driver to identify
+ the i/o the interrupt is associated with, or to recognize
+ the interrupt as unsolicited.
+ irb - interruption response block which contains the accumulated
+ status.
+The device driver is called from the common ccw_device layer and can retrieve
+information about the interrupt from the irb parameter.
+1.3 ccwgroup devices
+The ccwgroup mechanism is designed to handle devices consisting of multiple ccw
+devices, like lcs or ctc.
+The ccw driver provides a 'group' attribute. Piping bus ids of ccw devices to
+this attributes creates a ccwgroup device consisting of these ccw devices (if
+possible). This ccwgroup device can be set online or offline just like a normal
+ccw device.
+Each ccwgroup device also provides an 'ungroup' attribute to destroy the device
+again (only when offline). This is a generic ccwgroup mechanism (the driver does
+not need to implement anything beyond normal removal routines).
+To implement a ccwgroup driver, please refer to include/asm/ccwgroup.h. Keep in
+mind that most drivers will need to implement both a ccwgroup and a ccw driver
+(unless you have a meta ccw driver, like cu3088 for lcs and ctc).
+2. Channel paths
+Channel paths show up, like subchannels, under the channel subsystem root (css0)
+and are called 'chp0.<chpid>'. They have no driver and do not belong to any bus.
+Please note, that unlike /proc/chpids in 2.4, the channel path objects reflect
+only the logical state and not the physical state, since we cannot track the
+latter consistently due to lacking machine support (we don't need to be aware
+of anyway).
+status - Can be 'online' or 'offline'.
+ Piping 'on' or 'off' sets the chpid logically online/offline.
+ Piping 'on' to an online chpid triggers path reprobing for all devices
+ the chpid connects to. This can be used to force the kernel to re-use
+ a channel path the user knows to be online, but the machine hasn't
+ created a machine check for.
+3. System devices
+Note: cpus may yet be added here.
+3.1 xpram
+xpram shows up under sys/ as 'xpram'.
+4. Other devices
+4.1 Netiucv
+The netiucv driver creates an attribute 'connection' under
+bus/iucv/drivers/netiucv. Piping to this attibute creates a new netiucv
+connection to the specified host.
+Netiucv connections show up under devices/iucv/ as "netiucv<ifnum>". The interface
+number is assigned sequentially to the connections defined via the 'connection'
+user - shows the connection partner.
+buffer - maximum buffer size.
+ Pipe to it to change buffer size.