1 VME Device Drivers
2 ==================
3
4 Driver registration
5 -------------------
6
7 As with other subsystems within the Linux kernel, VME device drivers register
8 with the VME subsystem, typically called from the devices init routine. This is
9 achieved via a call to :c:func:`vme_register_driver`.
10
11 A pointer to a structure of type :c:type:`struct vme_driver <vme_driver>` must
12 be provided to the registration function. Along with the maximum number of
13 devices your driver is able to support.
14
15 At the minimum, the '.name', '.match' and '.probe' elements of
16 :c:type:`struct vme_driver <vme_driver>` should be correctly set. The '.name'
17 element is a pointer to a string holding the device driver's name.
18
19 The '.match' function allows control over which VME devices should be registered
20 with the driver. The match function should return 1 if a device should be
21 probed and 0 otherwise. This example match function (from vme_user.c) limits
22 the number of devices probed to one:
23
24 .. code-block:: c
25
26 #define USER_BUS_MAX 1
27 ...
28 static int vme_user_match(struct vme_dev *vdev)
29 {
30 if (vdev->id.num >= USER_BUS_MAX)
31 return 0;
32 return 1;
33 }
34
35 The '.probe' element should contain a pointer to the probe routine. The
36 probe routine is passed a :c:type:`struct vme_dev <vme_dev>` pointer as an
37 argument.
38
39 Here, the 'num' field refers to the sequential device ID for this specific
40 driver. The bridge number (or bus number) can be accessed using
41 dev->bridge->num.
42
43 A function is also provided to unregister the driver from the VME core called
44 :c:func:`vme_unregister_driver` and should usually be called from the device
45 driver's exit routine.
46
47
48 Resource management
49 -------------------
50
51 Once a driver has registered with the VME core the provided match routine will
52 be called the number of times specified during the registration. If a match
53 succeeds, a non-zero value should be returned. A zero return value indicates
54 failure. For all successful matches, the probe routine of the corresponding
55 driver is called. The probe routine is passed a pointer to the devices
56 device structure. This pointer should be saved, it will be required for
57 requesting VME resources.
58
59 The driver can request ownership of one or more master windows
60 (:c:func:`vme_master_request`), slave windows (:c:func:`vme_slave_request`)
61 and/or dma channels (:c:func:`vme_dma_request`). Rather than allowing the device
62 driver to request a specific window or DMA channel (which may be used by a
63 different driver) the API allows a resource to be assigned based on the required
64 attributes of the driver in question. For slave windows these attributes are
65 split into the VME address spaces that need to be accessed in 'aspace' and VME
66 bus cycle types required in 'cycle'. Master windows add a further set of
67 attributes in 'width' specifying the required data transfer widths. These
68 attributes are defined as bitmasks and as such any combination of the
69 attributes can be requested for a single window, the core will assign a window
70 that meets the requirements, returning a pointer of type vme_resource that
71 should be used to identify the allocated resource when it is used. For DMA
72 controllers, the request function requires the potential direction of any
73 transfers to be provided in the route attributes. This is typically VME-to-MEM
74 and/or MEM-to-VME, though some hardware can support VME-to-VME and MEM-to-MEM
75 transfers as well as test pattern generation. If an unallocated window fitting
76 the requirements can not be found a NULL pointer will be returned.
77
78 Functions are also provided to free window allocations once they are no longer
79 required. These functions (:c:func:`vme_master_free`, :c:func:`vme_slave_free`
80 and :c:func:`vme_dma_free`) should be passed the pointer to the resource
81 provided during resource allocation.
82
83
84 Master windows
85 --------------
86
87 Master windows provide access from the local processor[s] out onto the VME bus.
88 The number of windows available and the available access modes is dependent on
89 the underlying chipset. A window must be configured before it can be used.
90
91
92 Master window configuration
93 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
94
95 Once a master window has been assigned :c:func:`vme_master_set` can be used to
96 configure it and :c:func:`vme_master_get` to retrieve the current settings. The
97 address spaces, transfer widths and cycle types are the same as described
98 under resource management, however some of the options are mutually exclusive.
99 For example, only one address space may be specified.
100
101
102 Master window access
103 ~~~~~~~~~~~~~~~~~~~~
104
105 The function :c:func:`vme_master_read` can be used to read from and
106 :c:func:`vme_master_write` used to write to configured master windows.
107
108 In addition to simple reads and writes, :c:func:`vme_master_rmw` is provided to
109 do a read-modify-write transaction. Parts of a VME window can also be mapped
110 into user space memory using :c:func:`vme_master_mmap`.
111
112
113 Slave windows
114 -------------
115
116 Slave windows provide devices on the VME bus access into mapped portions of the
117 local memory. The number of windows available and the access modes that can be
118 used is dependent on the underlying chipset. A window must be configured before
119 it can be used.
120
121
122 Slave window configuration
123 ~~~~~~~~~~~~~~~~~~~~~~~~~~
124
125 Once a slave window has been assigned :c:func:`vme_slave_set` can be used to
126 configure it and :c:func:`vme_slave_get` to retrieve the current settings.
127
128 The address spaces, transfer widths and cycle types are the same as described
129 under resource management, however some of the options are mutually exclusive.
130 For example, only one address space may be specified.
131
132
133 Slave window buffer allocation
134 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
135
136 Functions are provided to allow the user to allocate
137 (:c:func:`vme_alloc_consistent`) and free (:c:func:`vme_free_consistent`)
138 contiguous buffers which will be accessible by the VME bridge. These functions
139 do not have to be used, other methods can be used to allocate a buffer, though
140 care must be taken to ensure that they are contiguous and accessible by the VME
141 bridge.
142
143
144 Slave window access
145 ~~~~~~~~~~~~~~~~~~~
146
147 Slave windows map local memory onto the VME bus, the standard methods for
148 accessing memory should be used.
149
150
151 DMA channels
152 ------------
153
154 The VME DMA transfer provides the ability to run link-list DMA transfers. The
155 API introduces the concept of DMA lists. Each DMA list is a link-list which can
156 be passed to a DMA controller. Multiple lists can be created, extended,
157 executed, reused and destroyed.
158
159
160 List Management
161 ~~~~~~~~~~~~~~~
162
163 The function :c:func:`vme_new_dma_list` is provided to create and
164 :c:func:`vme_dma_list_free` to destroy DMA lists. Execution of a list will not
165 automatically destroy the list, thus enabling a list to be reused for repetitive
166 tasks.
167
168
169 List Population
170 ~~~~~~~~~~~~~~~
171
172 An item can be added to a list using :c:func:`vme_dma_list_add` (the source and
173 destination attributes need to be created before calling this function, this is
174 covered under "Transfer Attributes").
175
176 .. note::
177
178 The detailed attributes of the transfers source and destination
179 are not checked until an entry is added to a DMA list, the request
180 for a DMA channel purely checks the directions in which the
181 controller is expected to transfer data. As a result it is
182 possible for this call to return an error, for example if the
183 source or destination is in an unsupported VME address space.
184
185 Transfer Attributes
186 ~~~~~~~~~~~~~~~~~~~
187
188 The attributes for the source and destination are handled separately from adding
189 an item to a list. This is due to the diverse attributes required for each type
190 of source and destination. There are functions to create attributes for PCI, VME
191 and pattern sources and destinations (where appropriate):
192
193 - PCI source or destination: :c:func:`vme_dma_pci_attribute`
194 - VME source or destination: :c:func:`vme_dma_vme_attribute`
195 - Pattern source: :c:func:`vme_dma_pattern_attribute`
196
197 The function :c:func:`vme_dma_free_attribute` should be used to free an
198 attribute.
199
200
201 List Execution
202 ~~~~~~~~~~~~~~
203
204 The function :c:func:`vme_dma_list_exec` queues a list for execution and will
205 return once the list has been executed.
206
207
208 Interrupts
209 ----------
210
211 The VME API provides functions to attach and detach callbacks to specific VME
212 level and status ID combinations and for the generation of VME interrupts with
213 specific VME level and status IDs.
214
215
216 Attaching Interrupt Handlers
217 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
218
219 The function :c:func:`vme_irq_request` can be used to attach and
220 :c:func:`vme_irq_free` to free a specific VME level and status ID combination.
221 Any given combination can only be assigned a single callback function. A void
222 pointer parameter is provided, the value of which is passed to the callback
223 function, the use of this pointer is user undefined. The callback parameters are
224 as follows. Care must be taken in writing a callback function, callback
225 functions run in interrupt context:
226
227 .. code-block:: c
228
229 void callback(int level, int statid, void *priv);
230
231
232 Interrupt Generation
233 ~~~~~~~~~~~~~~~~~~~~
234
235 The function :c:func:`vme_irq_generate` can be used to generate a VME interrupt
236 at a given VME level and VME status ID.
237
238
239 Location monitors
240 -----------------
241
242 The VME API provides the following functionality to configure the location
243 monitor.
244
245
246 Location Monitor Management
247 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
248
249 The function :c:func:`vme_lm_request` is provided to request the use of a block
250 of location monitors and :c:func:`vme_lm_free` to free them after they are no
251 longer required. Each block may provide a number of location monitors,
252 monitoring adjacent locations. The function :c:func:`vme_lm_count` can be used
253 to determine how many locations are provided.
254
255
256 Location Monitor Configuration
257 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
258
259 Once a bank of location monitors has been allocated, the function
260 :c:func:`vme_lm_set` is provided to configure the location and mode of the
261 location monitor. The function :c:func:`vme_lm_get` can be used to retrieve
262 existing settings.
263
264
265 Location Monitor Use
266 ~~~~~~~~~~~~~~~~~~~~
267
268 The function :c:func:`vme_lm_attach` enables a callback to be attached and
269 :c:func:`vme_lm_detach` allows on to be detached from each location monitor
270 location. Each location monitor can monitor a number of adjacent locations. The
271 callback function is declared as follows.
272
273 .. code-block:: c
274
275 void callback(void *data);
276
277
278 Slot Detection
279 --------------
280
281 The function :c:func:`vme_slot_num` returns the slot ID of the provided bridge.
282
283
284 Bus Detection
285 -------------
286
287 The function :c:func:`vme_bus_num` returns the bus ID of the provided bridge.
288
289
290 VME API
291 -------
292
293 .. kernel-doc:: drivers/staging/vme_user/vme.h
294 :internal:
295
296 .. kernel-doc:: drivers/staging/vme_user/vme.c
297 :export:
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