1 ==================== 1 ====================
2 DMA Engine API Guide 2 DMA Engine API Guide
3 ==================== 3 ====================
4 4
5 Vinod Koul <vinod dot koul at intel.com> 5 Vinod Koul <vinod dot koul at intel.com>
6 6
7 .. note:: For DMA Engine usage in async_tx ple 7 .. note:: For DMA Engine usage in async_tx please see:
8 ``Documentation/crypto/async-tx-api. 8 ``Documentation/crypto/async-tx-api.rst``
9 9
10 10
11 Below is a guide to device driver writers on h 11 Below is a guide to device driver writers on how to use the Slave-DMA API of the
12 DMA Engine. This is applicable only for slave 12 DMA Engine. This is applicable only for slave DMA usage only.
13 13
14 DMA usage 14 DMA usage
15 ========= 15 =========
16 16
17 The slave DMA usage consists of following step 17 The slave DMA usage consists of following steps:
18 18
19 - Allocate a DMA slave channel 19 - Allocate a DMA slave channel
20 20
21 - Set slave and controller specific parameters 21 - Set slave and controller specific parameters
22 22
23 - Get a descriptor for transaction 23 - Get a descriptor for transaction
24 24
25 - Submit the transaction 25 - Submit the transaction
26 26
27 - Issue pending requests and wait for callback 27 - Issue pending requests and wait for callback notification
28 28
29 The details of these operations are: 29 The details of these operations are:
30 30
31 1. Allocate a DMA slave channel 31 1. Allocate a DMA slave channel
32 32
33 Channel allocation is slightly different in 33 Channel allocation is slightly different in the slave DMA context,
34 client drivers typically need a channel fro 34 client drivers typically need a channel from a particular DMA
35 controller only and even in some cases a sp 35 controller only and even in some cases a specific channel is desired.
36 To request a channel dma_request_chan() API 36 To request a channel dma_request_chan() API is used.
37 37
38 Interface: 38 Interface:
39 39
40 .. code-block:: c 40 .. code-block:: c
41 41
42 struct dma_chan *dma_request_chan(struct 42 struct dma_chan *dma_request_chan(struct device *dev, const char *name);
43 43
44 Which will find and return the ``name`` DMA 44 Which will find and return the ``name`` DMA channel associated with the 'dev'
45 device. The association is done via DT, ACP 45 device. The association is done via DT, ACPI or board file based
46 dma_slave_map matching table. 46 dma_slave_map matching table.
47 47
48 A channel allocated via this interface is e 48 A channel allocated via this interface is exclusive to the caller,
49 until dma_release_channel() is called. 49 until dma_release_channel() is called.
50 50
51 2. Set slave and controller specific parameter 51 2. Set slave and controller specific parameters
52 52
53 Next step is always to pass some specific i 53 Next step is always to pass some specific information to the DMA
54 driver. Most of the generic information whi 54 driver. Most of the generic information which a slave DMA can use
55 is in struct dma_slave_config. This allows 55 is in struct dma_slave_config. This allows the clients to specify
56 DMA direction, DMA addresses, bus widths, D 56 DMA direction, DMA addresses, bus widths, DMA burst lengths etc
57 for the peripheral. 57 for the peripheral.
58 58
59 If some DMA controllers have more parameter 59 If some DMA controllers have more parameters to be sent then they
60 should try to embed struct dma_slave_config 60 should try to embed struct dma_slave_config in their controller
61 specific structure. That gives flexibility 61 specific structure. That gives flexibility to client to pass more
62 parameters, if required. 62 parameters, if required.
63 63
64 Interface: 64 Interface:
65 65
66 .. code-block:: c 66 .. code-block:: c
67 67
68 int dmaengine_slave_config(struct dma_ch 68 int dmaengine_slave_config(struct dma_chan *chan,
69 struct dma_slave_confi 69 struct dma_slave_config *config)
70 70
71 Please see the dma_slave_config structure d 71 Please see the dma_slave_config structure definition in dmaengine.h
72 for a detailed explanation of the struct me 72 for a detailed explanation of the struct members. Please note
73 that the 'direction' member will be going a 73 that the 'direction' member will be going away as it duplicates the
74 direction given in the prepare call. 74 direction given in the prepare call.
75 75
76 3. Get a descriptor for transaction 76 3. Get a descriptor for transaction
77 77
78 For slave usage the various modes of slave t 78 For slave usage the various modes of slave transfers supported by the
79 DMA-engine are: 79 DMA-engine are:
80 80
81 - slave_sg: DMA a list of scatter gather buf 81 - slave_sg: DMA a list of scatter gather buffers from/to a peripheral
82 82
83 - peripheral_dma_vec: DMA an array of scatte <<
84 peripheral. Similar to slave_sg, but uses <<
85 structures instead of a scatterlist. <<
86 <<
87 - dma_cyclic: Perform a cyclic DMA operation 83 - dma_cyclic: Perform a cyclic DMA operation from/to a peripheral till the
88 operation is explicitly stopped. 84 operation is explicitly stopped.
89 85
90 - interleaved_dma: This is common to Slave a 86 - interleaved_dma: This is common to Slave as well as M2M clients. For slave
91 address of devices' fifo could be already 87 address of devices' fifo could be already known to the driver.
92 Various types of operations could be expre 88 Various types of operations could be expressed by setting
93 appropriate values to the 'dma_interleaved 89 appropriate values to the 'dma_interleaved_template' members. Cyclic
94 interleaved DMA transfers are also possibl 90 interleaved DMA transfers are also possible if supported by the channel by
95 setting the DMA_PREP_REPEAT transfer flag. 91 setting the DMA_PREP_REPEAT transfer flag.
96 92
97 A non-NULL return of this transfer API repre 93 A non-NULL return of this transfer API represents a "descriptor" for
98 the given transaction. 94 the given transaction.
99 95
100 Interface: 96 Interface:
101 97
102 .. code-block:: c 98 .. code-block:: c
103 99
104 struct dma_async_tx_descriptor *dmaengine 100 struct dma_async_tx_descriptor *dmaengine_prep_slave_sg(
105 struct dma_chan *chan, struct 101 struct dma_chan *chan, struct scatterlist *sgl,
106 unsigned int sg_len, enum dma_ 102 unsigned int sg_len, enum dma_data_direction direction,
107 unsigned long flags); <<
108 <<
109 struct dma_async_tx_descriptor *dmaengine <<
110 struct dma_chan *chan, const s <<
111 size_t nents, enum dma_data_di <<
112 unsigned long flags); 103 unsigned long flags);
113 104
114 struct dma_async_tx_descriptor *dmaengine 105 struct dma_async_tx_descriptor *dmaengine_prep_dma_cyclic(
115 struct dma_chan *chan, dma_add 106 struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,
116 size_t period_len, enum dma_da 107 size_t period_len, enum dma_data_direction direction);
117 108
118 struct dma_async_tx_descriptor *dmaengine 109 struct dma_async_tx_descriptor *dmaengine_prep_interleaved_dma(
119 struct dma_chan *chan, struct 110 struct dma_chan *chan, struct dma_interleaved_template *xt,
120 unsigned long flags); 111 unsigned long flags);
121 112
122 The peripheral driver is expected to have ma 113 The peripheral driver is expected to have mapped the scatterlist for
123 the DMA operation prior to calling dmaengine 114 the DMA operation prior to calling dmaengine_prep_slave_sg(), and must
124 keep the scatterlist mapped until the DMA op 115 keep the scatterlist mapped until the DMA operation has completed.
125 The scatterlist must be mapped using the DMA 116 The scatterlist must be mapped using the DMA struct device.
126 If a mapping needs to be synchronized later, 117 If a mapping needs to be synchronized later, dma_sync_*_for_*() must be
127 called using the DMA struct device, too. 118 called using the DMA struct device, too.
128 So, normal setup should look like this: 119 So, normal setup should look like this:
129 120
130 .. code-block:: c 121 .. code-block:: c
131 122
132 struct device *dma_dev = dmaengine_get_dm 123 struct device *dma_dev = dmaengine_get_dma_device(chan);
133 124
134 nr_sg = dma_map_sg(dma_dev, sgl, sg_len); 125 nr_sg = dma_map_sg(dma_dev, sgl, sg_len);
135 if (nr_sg == 0) 126 if (nr_sg == 0)
136 /* error */ 127 /* error */
137 128
138 desc = dmaengine_prep_slave_sg(chan, s 129 desc = dmaengine_prep_slave_sg(chan, sgl, nr_sg, direction, flags);
139 130
140 Once a descriptor has been obtained, the cal 131 Once a descriptor has been obtained, the callback information can be
141 added and the descriptor must then be submit 132 added and the descriptor must then be submitted. Some DMA engine
142 drivers may hold a spinlock between a succes 133 drivers may hold a spinlock between a successful preparation and
143 submission so it is important that these two 134 submission so it is important that these two operations are closely
144 paired. 135 paired.
145 136
146 .. note:: 137 .. note::
147 138
148 Although the async_tx API specifies that 139 Although the async_tx API specifies that completion callback
149 routines cannot submit any new operations 140 routines cannot submit any new operations, this is not the
150 case for slave/cyclic DMA. 141 case for slave/cyclic DMA.
151 142
152 For slave DMA, the subsequent transaction 143 For slave DMA, the subsequent transaction may not be available
153 for submission prior to callback function 144 for submission prior to callback function being invoked, so
154 slave DMA callbacks are permitted to prep 145 slave DMA callbacks are permitted to prepare and submit a new
155 transaction. 146 transaction.
156 147
157 For cyclic DMA, a callback function may w 148 For cyclic DMA, a callback function may wish to terminate the
158 DMA via dmaengine_terminate_async(). 149 DMA via dmaengine_terminate_async().
159 150
160 Therefore, it is important that DMA engin 151 Therefore, it is important that DMA engine drivers drop any
161 locks before calling the callback functio 152 locks before calling the callback function which may cause a
162 deadlock. 153 deadlock.
163 154
164 Note that callbacks will always be invoke 155 Note that callbacks will always be invoked from the DMA
165 engines tasklet, never from interrupt con 156 engines tasklet, never from interrupt context.
166 157
167 **Optional: per descriptor metadata** 158 **Optional: per descriptor metadata**
168 159
169 DMAengine provides two ways for metadata sup 160 DMAengine provides two ways for metadata support.
170 161
171 DESC_METADATA_CLIENT 162 DESC_METADATA_CLIENT
172 163
173 The metadata buffer is allocated/provided 164 The metadata buffer is allocated/provided by the client driver and it is
174 attached to the descriptor. 165 attached to the descriptor.
175 166
176 .. code-block:: c 167 .. code-block:: c
177 168
178 int dmaengine_desc_attach_metadata(struct 169 int dmaengine_desc_attach_metadata(struct dma_async_tx_descriptor *desc,
179 void *data, 170 void *data, size_t len);
180 171
181 DESC_METADATA_ENGINE 172 DESC_METADATA_ENGINE
182 173
183 The metadata buffer is allocated/managed b 174 The metadata buffer is allocated/managed by the DMA driver. The client
184 driver can ask for the pointer, maximum si 175 driver can ask for the pointer, maximum size and the currently used size of
185 the metadata and can directly update or re 176 the metadata and can directly update or read it.
186 177
187 Because the DMA driver manages the memory 178 Because the DMA driver manages the memory area containing the metadata,
188 clients must make sure that they do not tr 179 clients must make sure that they do not try to access or get the pointer
189 after their transfer completion callback h 180 after their transfer completion callback has run for the descriptor.
190 If no completion callback has been defined 181 If no completion callback has been defined for the transfer, then the
191 metadata must not be accessed after issue_ 182 metadata must not be accessed after issue_pending.
192 In other words: if the aim is to read back 183 In other words: if the aim is to read back metadata after the transfer is
193 completed, then the client must use comple 184 completed, then the client must use completion callback.
194 185
195 .. code-block:: c 186 .. code-block:: c
196 187
197 void *dmaengine_desc_get_metadata_ptr(str 188 void *dmaengine_desc_get_metadata_ptr(struct dma_async_tx_descriptor *desc,
198 size_t *payload_len, size_t *m 189 size_t *payload_len, size_t *max_len);
199 190
200 int dmaengine_desc_set_metadata_len(struc 191 int dmaengine_desc_set_metadata_len(struct dma_async_tx_descriptor *desc,
201 size_t payload_len); 192 size_t payload_len);
202 193
203 Client drivers can query if a given mode is 194 Client drivers can query if a given mode is supported with:
204 195
205 .. code-block:: c 196 .. code-block:: c
206 197
207 bool dmaengine_is_metadata_mode_supported 198 bool dmaengine_is_metadata_mode_supported(struct dma_chan *chan,
208 enum dma_desc_metadata_mode mo 199 enum dma_desc_metadata_mode mode);
209 200
210 Depending on the used mode client drivers mu 201 Depending on the used mode client drivers must follow different flow.
211 202
212 DESC_METADATA_CLIENT 203 DESC_METADATA_CLIENT
213 204
214 - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM: 205 - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM:
215 206
216 1. prepare the descriptor (dmaengine_pre 207 1. prepare the descriptor (dmaengine_prep_*)
217 construct the metadata in the client' 208 construct the metadata in the client's buffer
218 2. use dmaengine_desc_attach_metadata() 209 2. use dmaengine_desc_attach_metadata() to attach the buffer to the
219 descriptor 210 descriptor
220 3. submit the transfer 211 3. submit the transfer
221 212
222 - DMA_DEV_TO_MEM: 213 - DMA_DEV_TO_MEM:
223 214
224 1. prepare the descriptor (dmaengine_pre 215 1. prepare the descriptor (dmaengine_prep_*)
225 2. use dmaengine_desc_attach_metadata() 216 2. use dmaengine_desc_attach_metadata() to attach the buffer to the
226 descriptor 217 descriptor
227 3. submit the transfer 218 3. submit the transfer
228 4. when the transfer is completed, the m 219 4. when the transfer is completed, the metadata should be available in the
229 attached buffer 220 attached buffer
230 221
231 DESC_METADATA_ENGINE 222 DESC_METADATA_ENGINE
232 223
233 - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM: 224 - DMA_MEM_TO_DEV / DEV_MEM_TO_MEM:
234 225
235 1. prepare the descriptor (dmaengine_pre 226 1. prepare the descriptor (dmaengine_prep_*)
236 2. use dmaengine_desc_get_metadata_ptr() 227 2. use dmaengine_desc_get_metadata_ptr() to get the pointer to the
237 engine's metadata area 228 engine's metadata area
238 3. update the metadata at the pointer 229 3. update the metadata at the pointer
239 4. use dmaengine_desc_set_metadata_len() 230 4. use dmaengine_desc_set_metadata_len() to tell the DMA engine the
240 amount of data the client has placed 231 amount of data the client has placed into the metadata buffer
241 5. submit the transfer 232 5. submit the transfer
242 233
243 - DMA_DEV_TO_MEM: 234 - DMA_DEV_TO_MEM:
244 235
245 1. prepare the descriptor (dmaengine_pre 236 1. prepare the descriptor (dmaengine_prep_*)
246 2. submit the transfer 237 2. submit the transfer
247 3. on transfer completion, use dmaengine 238 3. on transfer completion, use dmaengine_desc_get_metadata_ptr() to get
248 the pointer to the engine's metadata 239 the pointer to the engine's metadata area
249 4. read out the metadata from the pointe 240 4. read out the metadata from the pointer
250 241
251 .. note:: 242 .. note::
252 243
253 When DESC_METADATA_ENGINE mode is used th 244 When DESC_METADATA_ENGINE mode is used the metadata area for the descriptor
254 is no longer valid after the transfer has 245 is no longer valid after the transfer has been completed (valid up to the
255 point when the completion callback return 246 point when the completion callback returns if used).
256 247
257 Mixed use of DESC_METADATA_CLIENT / DESC_ 248 Mixed use of DESC_METADATA_CLIENT / DESC_METADATA_ENGINE is not allowed,
258 client drivers must use either of the mod 249 client drivers must use either of the modes per descriptor.
259 250
260 4. Submit the transaction 251 4. Submit the transaction
261 252
262 Once the descriptor has been prepared and t 253 Once the descriptor has been prepared and the callback information
263 added, it must be placed on the DMA engine 254 added, it must be placed on the DMA engine drivers pending queue.
264 255
265 Interface: 256 Interface:
266 257
267 .. code-block:: c 258 .. code-block:: c
268 259
269 dma_cookie_t dmaengine_submit(struct dma 260 dma_cookie_t dmaengine_submit(struct dma_async_tx_descriptor *desc)
270 261
271 This returns a cookie can be used to check 262 This returns a cookie can be used to check the progress of DMA engine
272 activity via other DMA engine calls not cov 263 activity via other DMA engine calls not covered in this document.
273 264
274 dmaengine_submit() will not start the DMA o 265 dmaengine_submit() will not start the DMA operation, it merely adds
275 it to the pending queue. For this, see step 266 it to the pending queue. For this, see step 5, dma_async_issue_pending.
276 267
277 .. note:: 268 .. note::
278 269
279 After calling ``dmaengine_submit()`` the 270 After calling ``dmaengine_submit()`` the submitted transfer descriptor
280 (``struct dma_async_tx_descriptor``) bel 271 (``struct dma_async_tx_descriptor``) belongs to the DMA engine.
281 Consequently, the client must consider i 272 Consequently, the client must consider invalid the pointer to that
282 descriptor. 273 descriptor.
283 274
284 5. Issue pending DMA requests and wait for cal 275 5. Issue pending DMA requests and wait for callback notification
285 276
286 The transactions in the pending queue can b 277 The transactions in the pending queue can be activated by calling the
287 issue_pending API. If channel is idle then 278 issue_pending API. If channel is idle then the first transaction in
288 queue is started and subsequent ones queued 279 queue is started and subsequent ones queued up.
289 280
290 On completion of each DMA operation, the ne 281 On completion of each DMA operation, the next in queue is started and
291 a tasklet triggered. The tasklet will then 282 a tasklet triggered. The tasklet will then call the client driver
292 completion callback routine for notificatio 283 completion callback routine for notification, if set.
293 284
294 Interface: 285 Interface:
295 286
296 .. code-block:: c 287 .. code-block:: c
297 288
298 void dma_async_issue_pending(struct dma_ 289 void dma_async_issue_pending(struct dma_chan *chan);
299 290
300 Further APIs 291 Further APIs
301 ------------ 292 ------------
302 293
303 1. Terminate APIs 294 1. Terminate APIs
304 295
305 .. code-block:: c 296 .. code-block:: c
306 297
307 int dmaengine_terminate_sync(struct dma_ 298 int dmaengine_terminate_sync(struct dma_chan *chan)
308 int dmaengine_terminate_async(struct dma 299 int dmaengine_terminate_async(struct dma_chan *chan)
309 int dmaengine_terminate_all(struct dma_c 300 int dmaengine_terminate_all(struct dma_chan *chan) /* DEPRECATED */
310 301
311 This causes all activity for the DMA channe 302 This causes all activity for the DMA channel to be stopped, and may
312 discard data in the DMA FIFO which hasn't b 303 discard data in the DMA FIFO which hasn't been fully transferred.
313 No callback functions will be called for an 304 No callback functions will be called for any incomplete transfers.
314 305
315 Two variants of this function are available 306 Two variants of this function are available.
316 307
317 dmaengine_terminate_async() might not wait 308 dmaengine_terminate_async() might not wait until the DMA has been fully
318 stopped or until any running complete callb 309 stopped or until any running complete callbacks have finished. But it is
319 possible to call dmaengine_terminate_async( 310 possible to call dmaengine_terminate_async() from atomic context or from
320 within a complete callback. dmaengine_synch 311 within a complete callback. dmaengine_synchronize() must be called before it
321 is safe to free the memory accessed by the 312 is safe to free the memory accessed by the DMA transfer or free resources
322 accessed from within the complete callback. 313 accessed from within the complete callback.
323 314
324 dmaengine_terminate_sync() will wait for th 315 dmaengine_terminate_sync() will wait for the transfer and any running
325 complete callbacks to finish before it retu 316 complete callbacks to finish before it returns. But the function must not be
326 called from atomic context or from within a 317 called from atomic context or from within a complete callback.
327 318
328 dmaengine_terminate_all() is deprecated and 319 dmaengine_terminate_all() is deprecated and should not be used in new code.
329 320
330 2. Pause API 321 2. Pause API
331 322
332 .. code-block:: c 323 .. code-block:: c
333 324
334 int dmaengine_pause(struct dma_chan *cha 325 int dmaengine_pause(struct dma_chan *chan)
335 326
336 This pauses activity on the DMA channel wit 327 This pauses activity on the DMA channel without data loss.
337 328
338 3. Resume API 329 3. Resume API
339 330
340 .. code-block:: c 331 .. code-block:: c
341 332
342 int dmaengine_resume(struct dma_chan *c 333 int dmaengine_resume(struct dma_chan *chan)
343 334
344 Resume a previously paused DMA channel. It 335 Resume a previously paused DMA channel. It is invalid to resume a
345 channel which is not currently paused. 336 channel which is not currently paused.
346 337
347 4. Check Txn complete 338 4. Check Txn complete
348 339
349 .. code-block:: c 340 .. code-block:: c
350 341
351 enum dma_status dma_async_is_tx_complete 342 enum dma_status dma_async_is_tx_complete(struct dma_chan *chan,
352 dma_cookie_t cookie, dma_cooki 343 dma_cookie_t cookie, dma_cookie_t *last, dma_cookie_t *used)
353 344
354 This can be used to check the status of the 345 This can be used to check the status of the channel. Please see
355 the documentation in include/linux/dmaengin 346 the documentation in include/linux/dmaengine.h for a more complete
356 description of this API. 347 description of this API.
357 348
358 This can be used in conjunction with dma_as 349 This can be used in conjunction with dma_async_is_complete() and
359 the cookie returned from dmaengine_submit() 350 the cookie returned from dmaengine_submit() to check for
360 completion of a specific DMA transaction. 351 completion of a specific DMA transaction.
361 352
362 .. note:: 353 .. note::
363 354
364 Not all DMA engine drivers can return re 355 Not all DMA engine drivers can return reliable information for
365 a running DMA channel. It is recommended 356 a running DMA channel. It is recommended that DMA engine users
366 pause or stop (via dmaengine_terminate_a 357 pause or stop (via dmaengine_terminate_all()) the channel before
367 using this API. 358 using this API.
368 359
369 5. Synchronize termination API 360 5. Synchronize termination API
370 361
371 .. code-block:: c 362 .. code-block:: c
372 363
373 void dmaengine_synchronize(struct dma_ch 364 void dmaengine_synchronize(struct dma_chan *chan)
374 365
375 Synchronize the termination of the DMA chan 366 Synchronize the termination of the DMA channel to the current context.
376 367
377 This function should be used after dmaengin 368 This function should be used after dmaengine_terminate_async() to synchronize
378 the termination of the DMA channel to the c 369 the termination of the DMA channel to the current context. The function will
379 wait for the transfer and any running compl 370 wait for the transfer and any running complete callbacks to finish before it
380 returns. 371 returns.
381 372
382 If dmaengine_terminate_async() is used to s 373 If dmaengine_terminate_async() is used to stop the DMA channel this function
383 must be called before it is safe to free me 374 must be called before it is safe to free memory accessed by previously
384 submitted descriptors or to free any resour 375 submitted descriptors or to free any resources accessed within the complete
385 callback of previously submitted descriptor 376 callback of previously submitted descriptors.
386 377
387 The behavior of this function is undefined 378 The behavior of this function is undefined if dma_async_issue_pending() has
388 been called between dmaengine_terminate_asy 379 been called between dmaengine_terminate_async() and this function.
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