Documentation/s390/driver-model.txt

   1 S/390 driver model interfaces
   2 -----------------------------
   3
   4 1. CCW devices
   5 --------------
   6
   7 All devices which can be addressed by means of ccws are called 'CCW devices' -
   8 even if they aren't actually driven by ccws.
   9
  10 All ccw devices are accessed via a subchannel, this is reflected in the
  11 structures under root/:
  12
  13 root/
  14      - sys
  15      - legacy
  16      - css0/
  17            - 0.0.0000/0.0.0815/
  18            - 0.0.0001/0.0.4711/
  19            - 0.0.0002/
  20            ...
  21
  22 In this example, device 0815 is accessed via subchannel 0, device 4711 via
  23 subchannel 1, and subchannel 2 is a non-I/O subchannel.
  24
  25 You should address a ccw device via its bus id (e.g. 0.0.4711); the device can
  26 be found under bus/ccw/devices/.
  27
  28 All ccw devices export some data via sysfs.
  29
  30 cutype:     The control unit type / model.
  31
  32 devtype:    The device type / model, if applicable.
  33
  34 availability: Can be 'good' or 'boxed'; 'no path' or 'no device' for
  35               disconnected devices.
  36
  37 online:     An interface to set the device online and offline.
  38             In the special case of the device being disconnected (see the
  39             notify function under 1.2), piping 0 to online will focibly delete
  40             the device.
  41
  42 The device drivers can add entries to export per-device data and interfaces.
  43
  44 There is also some data exported on a per-subchannel basis (see under
  45 bus/css/devices/):
  46
  47 chpids:     Via which chpids the device is connected.
  48
  49 pimpampom:  The path installed, path available and path operational masks.
  50
  51 There also might be additional data, for example for block devices.
  52
  53
  54 1.1 Bringing up a ccw device
  55 ----------------------------
  56
  57 This is done in several steps.
  58
  59 a. Each driver can provide one or more parameter interfaces where parameters can
  60    be specified. These interfaces are also in the driver's responsibility.
  61 b. After a. has been performed, if necessary, the device is finally brought up
  62    via the 'online' interface.
  63
  64
  65 1.2 Writing a driver for ccw devices
  66 ------------------------------------
  67
  68 The basic struct ccw_device and struct ccw_driver data structures can be found
  69 under include/asm/ccwdev.h.
  70
  71 struct ccw_device {
  72         spinlock_t *ccwlock;
  73         struct ccw_device_private *private;
  74         struct ccw_device_id id;
  75
  76         struct ccw_driver *drv;
  77         struct device dev;
  78         int online;
  79
  80         void (*handler) (struct ccw_device *dev, unsigned long intparm,
  81                          struct irb *irb);
  82 };
  83
  84 struct ccw_driver {
  85         struct module *owner;
  86         struct ccw_device_id *ids;
  87         int (*probe) (struct ccw_device *);
  88         int (*remove) (struct ccw_device *);
  89         int (*set_online) (struct ccw_device *);
  90         int (*set_offline) (struct ccw_device *);
  91         int (*notify) (struct ccw_device *, int);
  92         struct device_driver driver;
  93         char *name;
  94 };
  95
  96 The 'private' field contains data needed for internal i/o operation only, and
  97 is not available to the device driver.
  98
  99 Each driver should declare in a MODULE_DEVICE_TABLE into which CU types/models
 100 and/or device types/models it is interested. This information can later be found
 101 found in the struct ccw_device_id fields:
 102
 103 struct ccw_device_id {
 104         __u16   match_flags;
 105
 106         __u16   cu_type;
 107         __u16   dev_type;
 108         __u8    cu_model;
 109         __u8    dev_model;
 110
 111         unsigned long driver_info;
 112 };
 113
 114 The functions in ccw_driver should be used in the following way:
 115 probe:   This function is called by the device layer for each device the driver
 116          is interested in. The driver should only allocate private structures
 117          to put in dev->driver_data and create attributes (if needed). Also,
 118          the interrupt handler (see below) should be set here.
 119
 120 int (*probe) (struct ccw_device *cdev);
 121
 122 Parameters:  cdev     - the device to be probed.
 123
 124
 125 remove:  This function is called by the device layer upon removal of the driver,
 126          the device or the module. The driver should perform cleanups here.
 127
 128 int (*remove) (struct ccw_device *cdev);
 129
 130 Parameters:   cdev    - the device to be removed.
 131
 132
 133 set_online: This function is called by the common I/O layer when the device is
 134             activated via the 'online' attribute. The driver should finally
 135             setup and activate the device here.
 136
 137 int (*set_online) (struct ccw_device *);
 138
 139 Parameters:   cdev      - the device to be activated. The common layer has
 140                           verified that the device is not already online.
 141
 142
 143 set_offline: This function is called by the common I/O layer when the device is
 144              de-activated via the 'online' attribute. The driver should shut
 145              down the device, but not de-allocate its private data.
 146
 147 int (*set_offline) (struct ccw_device *);
 148
 149 Parameters:   cdev       - the device to be deactivated. The common layer has
 150                            verified that the device is online.
 151
 152
 153 notify: This function is called by the common I/O layer for some state changes
 154         of the device.
 155         Signalled to the driver are:
 156         * In online state, device detached (CIO_GONE) or last path gone
 157           (CIO_NO_PATH). The driver must return !0 to keep the device; for
 158           return code 0, the device will be deleted as usual (also when no
 159           notify function is registerd). If the driver wants to keep the
 160           device, it is moved into disconnected state.
 161         * In disconnected state, device operational again (CIO_OPER). The
 162           common I/O layer performs some sanity checks on device number and
 163           Device / CU to be reasonably sure if it is still the same device.
 164           If not, the old device is removed and a new one registered. By the
 165           return code of the notify function the device driver signals if it
 166           wants the device back: !0 for keeping, 0 to make the device being
 167           removed and re-registered.
 168
 169 int (*notify) (struct ccw_device *, int);
 170
 171 Parameters:   cdev    - the device whose state changed.
 172               event   - the event that happened. This can be one of CIO_GONE,
 173                         CIO_NO_PATH or CIO_OPER.
 174
 175 The handler field of the struct ccw_device is meant to be set to the interrupt
 176 handler for the device. In order to accommodate drivers which use several
 177 distinct handlers (e.g. multi subchannel devices), this is a member of ccw_device
 178 instead of ccw_driver.
 179 The handler is registered with the common layer during set_online() processing
 180 before the driver is called, and is deregistered during set_offline() after the
 181 driver has been called. Also, after registering / before deregistering, path
 182 grouping resp. disbanding of the path group (if applicable) are performed.
 183
 184 void (*handler) (struct ccw_device *dev, unsigned long intparm, struct irb *irb);
 185
 186 Parameters:     dev     - the device the handler is called for
 187                 intparm - the intparm which allows the device driver to identify
 188                           the i/o the interrupt is associated with, or to recognize
 189                           the interrupt as unsolicited.
 190                 irb     - interruption response block which contains the accumulated
 191                           status.
 192
 193 The device driver is called from the common ccw_device layer and can retrieve
 194 information about the interrupt from the irb parameter.
 195
 196
 197 1.3 ccwgroup devices
 198 --------------------
 199
 200 The ccwgroup mechanism is designed to handle devices consisting of multiple ccw
 201 devices, like lcs or ctc.
 202
 203 The ccw driver provides a 'group' attribute. Piping bus ids of ccw devices to
 204 this attributes creates a ccwgroup device consisting of these ccw devices (if
 205 possible). This ccwgroup device can be set online or offline just like a normal
 206 ccw device.
 207
 208 Each ccwgroup device also provides an 'ungroup' attribute to destroy the device
 209 again (only when offline). This is a generic ccwgroup mechanism (the driver does
 210 not need to implement anything beyond normal removal routines).
 211
 212 To implement a ccwgroup driver, please refer to include/asm/ccwgroup.h. Keep in
 213 mind that most drivers will need to implement both a ccwgroup and a ccw driver
 214 (unless you have a meta ccw driver, like cu3088 for lcs and ctc).
 215
 216
 217 2. Channel paths
 218 -----------------
 219
 220 Channel paths show up, like subchannels, under the channel subsystem root (css0)
 221 and are called 'chp0.<chpid>'. They have no driver and do not belong to any bus.
 222 Please note, that unlike /proc/chpids in 2.4, the channel path objects reflect
 223 only the logical state and not the physical state, since we cannot track the
 224 latter consistently due to lacking machine support (we don't need to be aware
 225 of anyway).
 226
 227 status - Can be 'online' or 'offline'.
 228          Piping 'on' or 'off' sets the chpid logically online/offline.
 229          Piping 'on' to an online chpid triggers path reprobing for all devices
 230          the chpid connects to. This can be used to force the kernel to re-use
 231          a channel path the user knows to be online, but the machine hasn't
 232          created a machine check for.
 233
 234
 235 3. System devices
 236 -----------------
 237
 238 Note: cpus may yet be added here.
 239
 240 3.1 xpram
 241 ---------
 242
 243 xpram shows up under sys/ as 'xpram'.
 244
 245
 246 4. Other devices
 247 ----------------
 248
 249 4.1 Netiucv
 250 -----------
 251
 252 The netiucv driver creates an attribute 'connection' under
 253 bus/iucv/drivers/netiucv. Piping to this attibute creates a new netiucv
 254 connection to the specified host.
 255
 256 Netiucv connections show up under devices/iucv/ as "netiucv<ifnum>". The interface
 257 number is assigned sequentially to the connections defined via the 'connection'
 258 attribute.
 259
 260 user                      - shows the connection partner.
 261
 262 buffer                    - maximum buffer size.
 263                             Pipe to it to change buffer size.
 264
 265