1=============================
2S/390 driver model interfaces
3=============================
4
51. CCW devices
6--------------
7
8All devices which can be addressed by means of ccws are called 'CCW devices' -
9even if they aren't actually driven by ccws.
10
11All ccw devices are accessed via a subchannel, this is reflected in the
12structures under devices/::
13
14  devices/
15     - system/
16     - css0/
17	   - 0.0.0000/0.0.0815/
18	   - 0.0.0001/0.0.4711/
19	   - 0.0.0002/
20	   - 0.1.0000/0.1.1234/
21	   ...
22	   - defunct/
23
24In this example, device 0815 is accessed via subchannel 0 in subchannel set 0,
25device 4711 via subchannel 1 in subchannel set 0, and subchannel 2 is a non-I/O
26subchannel. Device 1234 is accessed via subchannel 0 in subchannel set 1.
27
28The subchannel named 'defunct' does not represent any real subchannel on the
29system; it is a pseudo subchannel where disconnected ccw devices are moved to
30if they are displaced by another ccw device becoming operational on their
31former subchannel. The ccw devices will be moved again to a proper subchannel
32if they become operational again on that subchannel.
33
34You should address a ccw device via its bus id (e.g. 0.0.4711); the device can
35be found under bus/ccw/devices/.
36
37All ccw devices export some data via sysfs.
38
39cutype:
40	The control unit type / model.
41
42devtype:
43	The device type / model, if applicable.
44
45availability:
46	      Can be 'good' or 'boxed'; 'no path' or 'no device' for
47	      disconnected devices.
48
49online:
50	    An interface to set the device online and offline.
51	    In the special case of the device being disconnected (see the
52	    notify function under 1.2), piping 0 to online will forcibly delete
53	    the device.
54
55The device drivers can add entries to export per-device data and interfaces.
56
57There is also some data exported on a per-subchannel basis (see under
58bus/css/devices/):
59
60chpids:
61	Via which chpids the device is connected.
62
63pimpampom:
64	The path installed, path available and path operational masks.
65
66There also might be additional data, for example for block devices.
67
68
691.1 Bringing up a ccw device
70----------------------------
71
72This is done in several steps.
73
74a. Each driver can provide one or more parameter interfaces where parameters can
75   be specified. These interfaces are also in the driver's responsibility.
76b. After a. has been performed, if necessary, the device is finally brought up
77   via the 'online' interface.
78
79
801.2 Writing a driver for ccw devices
81------------------------------------
82
83The basic struct ccw_device and struct ccw_driver data structures can be found
84under include/asm/ccwdev.h::
85
86  struct ccw_device {
87	spinlock_t *ccwlock;
88	struct ccw_device_private *private;
89	struct ccw_device_id id;
90
91	struct ccw_driver *drv;
92	struct device dev;
93	int online;
94
95	void (*handler) (struct ccw_device *dev, unsigned long intparm,
96			 struct irb *irb);
97  };
98
99  struct ccw_driver {
100	struct module *owner;
101	struct ccw_device_id *ids;
102	int (*probe) (struct ccw_device *);
103	int (*remove) (struct ccw_device *);
104	int (*set_online) (struct ccw_device *);
105	int (*set_offline) (struct ccw_device *);
106	int (*notify) (struct ccw_device *, int);
107	struct device_driver driver;
108	char *name;
109  };
110
111The 'private' field contains data needed for internal i/o operation only, and
112is not available to the device driver.
113
114Each driver should declare in a MODULE_DEVICE_TABLE into which CU types/models
115and/or device types/models it is interested. This information can later be found
116in the struct ccw_device_id fields::
117
118  struct ccw_device_id {
119	__u16   match_flags;
120
121	__u16   cu_type;
122	__u16   dev_type;
123	__u8    cu_model;
124	__u8    dev_model;
125
126	unsigned long driver_info;
127  };
128
129The functions in ccw_driver should be used in the following way:
130
131probe:
132	 This function is called by the device layer for each device the driver
133	 is interested in. The driver should only allocate private structures
134	 to put in dev->driver_data and create attributes (if needed). Also,
135	 the interrupt handler (see below) should be set here.
136
137::
138
139  int (*probe) (struct ccw_device *cdev);
140
141Parameters:
142		cdev
143			- the device to be probed.
144
145
146remove:
147	 This function is called by the device layer upon removal of the driver,
148	 the device or the module. The driver should perform cleanups here.
149
150::
151
152  int (*remove) (struct ccw_device *cdev);
153
154Parameters:
155		cdev
156			- the device to be removed.
157
158
159set_online:
160	    This function is called by the common I/O layer when the device is
161	    activated via the 'online' attribute. The driver should finally
162	    setup and activate the device here.
163
164::
165
166  int (*set_online) (struct ccw_device *);
167
168Parameters:
169		cdev
170			- the device to be activated. The common layer has
171			  verified that the device is not already online.
172
173
174set_offline: This function is called by the common I/O layer when the device is
175	     de-activated via the 'online' attribute. The driver should shut
176	     down the device, but not de-allocate its private data.
177
178::
179
180  int (*set_offline) (struct ccw_device *);
181
182Parameters:
183		cdev
184			- the device to be deactivated. The common layer has
185			   verified that the device is online.
186
187
188notify:
189	This function is called by the common I/O layer for some state changes
190	of the device.
191
192	Signalled to the driver are:
193
194	* In online state, device detached (CIO_GONE) or last path gone
195	  (CIO_NO_PATH). The driver must return !0 to keep the device; for
196	  return code 0, the device will be deleted as usual (also when no
197	  notify function is registered). If the driver wants to keep the
198	  device, it is moved into disconnected state.
199	* In disconnected state, device operational again (CIO_OPER). The
200	  common I/O layer performs some sanity checks on device number and
201	  Device / CU to be reasonably sure if it is still the same device.
202	  If not, the old device is removed and a new one registered. By the
203	  return code of the notify function the device driver signals if it
204	  wants the device back: !0 for keeping, 0 to make the device being
205	  removed and re-registered.
206
207::
208
209  int (*notify) (struct ccw_device *, int);
210
211Parameters:
212		cdev
213			- the device whose state changed.
214
215		event
216			- the event that happened. This can be one of CIO_GONE,
217			  CIO_NO_PATH or CIO_OPER.
218
219The handler field of the struct ccw_device is meant to be set to the interrupt
220handler for the device. In order to accommodate drivers which use several
221distinct handlers (e.g. multi subchannel devices), this is a member of ccw_device
222instead of ccw_driver.
223The handler is registered with the common layer during set_online() processing
224before the driver is called, and is deregistered during set_offline() after the
225driver has been called. Also, after registering / before deregistering, path
226grouping resp. disbanding of the path group (if applicable) are performed.
227
228::
229
230  void (*handler) (struct ccw_device *dev, unsigned long intparm, struct irb *irb);
231
232Parameters:     dev     - the device the handler is called for
233		intparm - the intparm which allows the device driver to identify
234			  the i/o the interrupt is associated with, or to recognize
235			  the interrupt as unsolicited.
236		irb     - interruption response block which contains the accumulated
237			  status.
238
239The device driver is called from the common ccw_device layer and can retrieve
240information about the interrupt from the irb parameter.
241
242
2431.3 ccwgroup devices
244--------------------
245
246The ccwgroup mechanism is designed to handle devices consisting of multiple ccw
247devices, like lcs or ctc.
248
249The ccw driver provides a 'group' attribute. Piping bus ids of ccw devices to
250this attributes creates a ccwgroup device consisting of these ccw devices (if
251possible). This ccwgroup device can be set online or offline just like a normal
252ccw device.
253
254Each ccwgroup device also provides an 'ungroup' attribute to destroy the device
255again (only when offline). This is a generic ccwgroup mechanism (the driver does
256not need to implement anything beyond normal removal routines).
257
258A ccw device which is a member of a ccwgroup device carries a pointer to the
259ccwgroup device in the driver_data of its device struct. This field must not be
260touched by the driver - it should use the ccwgroup device's driver_data for its
261private data.
262
263To implement a ccwgroup driver, please refer to include/asm/ccwgroup.h. Keep in
264mind that most drivers will need to implement both a ccwgroup and a ccw
265driver.
266
267
2682. Channel paths
269-----------------
270
271Channel paths show up, like subchannels, under the channel subsystem root (css0)
272and are called 'chp0.<chpid>'. They have no driver and do not belong to any bus.
273Please note, that unlike /proc/chpids in 2.4, the channel path objects reflect
274only the logical state and not the physical state, since we cannot track the
275latter consistently due to lacking machine support (we don't need to be aware
276of it anyway).
277
278status
279       - Can be 'online' or 'offline'.
280	 Piping 'on' or 'off' sets the chpid logically online/offline.
281	 Piping 'on' to an online chpid triggers path reprobing for all devices
282	 the chpid connects to. This can be used to force the kernel to re-use
283	 a channel path the user knows to be online, but the machine hasn't
284	 created a machine check for.
285
286type
287       - The physical type of the channel path.
288
289shared
290       - Whether the channel path is shared.
291
292cmg
293       - The channel measurement group.
294
2953. System devices
296-----------------
297
2983.1 xpram
299---------
300
301xpram shows up under devices/system/ as 'xpram'.
302
3033.2 cpus
304--------
305
306For each cpu, a directory is created under devices/system/cpu/. Each cpu has an
307attribute 'online' which can be 0 or 1.
308
309
3104. Other devices
311----------------
312
3134.1 Netiucv
314-----------
315
316The netiucv driver creates an attribute 'connection' under
317bus/iucv/drivers/netiucv. Piping to this attribute creates a new netiucv
318connection to the specified host.
319
320Netiucv connections show up under devices/iucv/ as "netiucv<ifnum>". The interface
321number is assigned sequentially to the connections defined via the 'connection'
322attribute.
323
324user
325    - shows the connection partner.
326
327buffer
328    - maximum buffer size. Pipe to it to change buffer size.
329