1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 2
3 .. _subdev: 3 .. _subdev:
4 4
5 ******************** 5 ********************
6 Sub-device Interface 6 Sub-device Interface
7 ******************** 7 ********************
8 8
9 The complex nature of V4L2 devices, where hard 9 The complex nature of V4L2 devices, where hardware is often made of
10 several integrated circuits that need to inter 10 several integrated circuits that need to interact with each other in a
11 controlled way, leads to complex V4L2 drivers. 11 controlled way, leads to complex V4L2 drivers. The drivers usually
12 reflect the hardware model in software, and mo 12 reflect the hardware model in software, and model the different hardware
13 components as software blocks called sub-devic 13 components as software blocks called sub-devices.
14 14
15 V4L2 sub-devices are usually kernel-only objec 15 V4L2 sub-devices are usually kernel-only objects. If the V4L2 driver
16 implements the media device API, they will aut 16 implements the media device API, they will automatically inherit from
17 media entities. Applications will be able to e 17 media entities. Applications will be able to enumerate the sub-devices
18 and discover the hardware topology using the m 18 and discover the hardware topology using the media entities, pads and
19 links enumeration API. 19 links enumeration API.
20 20
21 In addition to make sub-devices discoverable, 21 In addition to make sub-devices discoverable, drivers can also choose to
22 make them directly configurable by application 22 make them directly configurable by applications. When both the
23 sub-device driver and the V4L2 device driver s 23 sub-device driver and the V4L2 device driver support this, sub-devices
24 will feature a character device node on which 24 will feature a character device node on which ioctls can be called to
25 25
26 - query, read and write sub-devices controls 26 - query, read and write sub-devices controls
27 27
28 - subscribe and unsubscribe to events and ret 28 - subscribe and unsubscribe to events and retrieve them
29 29
30 - negotiate image formats on individual pads 30 - negotiate image formats on individual pads
31 31
32 - inspect and modify internal data routing be 32 - inspect and modify internal data routing between pads of the same entity
33 33
34 Sub-device character device nodes, conventiona 34 Sub-device character device nodes, conventionally named
35 ``/dev/v4l-subdev*``, use major number 81. 35 ``/dev/v4l-subdev*``, use major number 81.
36 36
37 Drivers may opt to limit the sub-device charac 37 Drivers may opt to limit the sub-device character devices to only expose
38 operations that do not modify the device state 38 operations that do not modify the device state. In such a case the sub-devices
39 are referred to as ``read-only`` in the rest o 39 are referred to as ``read-only`` in the rest of this documentation, and the
40 related restrictions are documented in individ 40 related restrictions are documented in individual ioctls.
41 41
42 42
43 Controls 43 Controls
44 ======== 44 ========
45 45
46 Most V4L2 controls are implemented by sub-devi 46 Most V4L2 controls are implemented by sub-device hardware. Drivers
47 usually merge all controls and expose them thr 47 usually merge all controls and expose them through video device nodes.
48 Applications can control all sub-devices throu 48 Applications can control all sub-devices through a single interface.
49 49
50 Complex devices sometimes implement the same c 50 Complex devices sometimes implement the same control in different pieces
51 of hardware. This situation is common in embed 51 of hardware. This situation is common in embedded platforms, where both
52 sensors and image processing hardware implemen 52 sensors and image processing hardware implement identical functions,
53 such as contrast adjustment, white balance or 53 such as contrast adjustment, white balance or faulty pixels correction.
54 As the V4L2 controls API doesn't support sever 54 As the V4L2 controls API doesn't support several identical controls in a
55 single device, all but one of the identical co 55 single device, all but one of the identical controls are hidden.
56 56
57 Applications can access those hidden controls 57 Applications can access those hidden controls through the sub-device
58 node with the V4L2 control API described in :r 58 node with the V4L2 control API described in :ref:`control`. The ioctls
59 behave identically as when issued on V4L2 devi 59 behave identically as when issued on V4L2 device nodes, with the
60 exception that they deal only with controls im 60 exception that they deal only with controls implemented in the
61 sub-device. 61 sub-device.
62 62
63 Depending on the driver, those controls might 63 Depending on the driver, those controls might also be exposed through
64 one (or several) V4L2 device nodes. 64 one (or several) V4L2 device nodes.
65 65
66 66
67 Events 67 Events
68 ====== 68 ======
69 69
70 V4L2 sub-devices can notify applications of ev 70 V4L2 sub-devices can notify applications of events as described in
71 :ref:`event`. The API behaves identically as w 71 :ref:`event`. The API behaves identically as when used on V4L2 device
72 nodes, with the exception that it only deals w 72 nodes, with the exception that it only deals with events generated by
73 the sub-device. Depending on the driver, those 73 the sub-device. Depending on the driver, those events might also be
74 reported on one (or several) V4L2 device nodes 74 reported on one (or several) V4L2 device nodes.
75 75
76 76
77 .. _pad-level-formats: 77 .. _pad-level-formats:
78 78
79 Pad-level Formats 79 Pad-level Formats
80 ================= 80 =================
81 81
82 .. warning:: 82 .. warning::
83 83
84 Pad-level formats are only applicable to v 84 Pad-level formats are only applicable to very complex devices that
85 need to expose low-level format configurat 85 need to expose low-level format configuration to user space. Generic
86 V4L2 applications do *not* need to use the 86 V4L2 applications do *not* need to use the API described in this
87 section. 87 section.
88 88
89 .. note:: 89 .. note::
90 90
91 For the purpose of this section, the term 91 For the purpose of this section, the term *format* means the
92 combination of media bus data format, fram 92 combination of media bus data format, frame width and frame height.
93 93
94 Image formats are typically negotiated on vide 94 Image formats are typically negotiated on video capture and output
95 devices using the format and 95 devices using the format and
96 :ref:`selection <VIDIOC_SUBDEV_G_SELECTION>` i 96 :ref:`selection <VIDIOC_SUBDEV_G_SELECTION>` ioctls. The driver is
97 responsible for configuring every block in the 97 responsible for configuring every block in the video pipeline according
98 to the requested format at the pipeline input 98 to the requested format at the pipeline input and/or output.
99 99
100 For complex devices, such as often found in em 100 For complex devices, such as often found in embedded systems, identical
101 image sizes at the output of a pipeline can be 101 image sizes at the output of a pipeline can be achieved using different
102 hardware configurations. One such example is s 102 hardware configurations. One such example is shown on
103 :ref:`pipeline-scaling`, where image scaling c 103 :ref:`pipeline-scaling`, where image scaling can be performed on both
104 the video sensor and the host image processing 104 the video sensor and the host image processing hardware.
105 105
106 106
107 .. _pipeline-scaling: 107 .. _pipeline-scaling:
108 108
109 .. kernel-figure:: pipeline.dot 109 .. kernel-figure:: pipeline.dot
110 :alt: pipeline.dot 110 :alt: pipeline.dot
111 :align: center 111 :align: center
112 112
113 Image Format Negotiation on Pipelines 113 Image Format Negotiation on Pipelines
114 114
115 High quality and high speed pipeline confi 115 High quality and high speed pipeline configuration
116 116
117 117
118 118
119 The sensor scaler is usually of less quality t 119 The sensor scaler is usually of less quality than the host scaler, but
120 scaling on the sensor is required to achieve h 120 scaling on the sensor is required to achieve higher frame rates.
121 Depending on the use case (quality vs. speed), 121 Depending on the use case (quality vs. speed), the pipeline must be
122 configured differently. Applications need to c 122 configured differently. Applications need to configure the formats at
123 every point in the pipeline explicitly. 123 every point in the pipeline explicitly.
124 124
125 Drivers that implement the :ref:`media API <me 125 Drivers that implement the :ref:`media API <media-controller-intro>`
126 can expose pad-level image format configuratio 126 can expose pad-level image format configuration to applications. When
127 they do, applications can use the 127 they do, applications can use the
128 :ref:`VIDIOC_SUBDEV_G_FMT <VIDIOC_SUBDEV_G_FMT 128 :ref:`VIDIOC_SUBDEV_G_FMT <VIDIOC_SUBDEV_G_FMT>` and
129 :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT 129 :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctls. to
130 negotiate formats on a per-pad basis. 130 negotiate formats on a per-pad basis.
131 131
132 Applications are responsible for configuring c 132 Applications are responsible for configuring coherent parameters on the
133 whole pipeline and making sure that connected 133 whole pipeline and making sure that connected pads have compatible
134 formats. The pipeline is checked for formats m 134 formats. The pipeline is checked for formats mismatch at
135 :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` time, 135 :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` time, and an ``EPIPE`` error
136 code is then returned if the configuration is 136 code is then returned if the configuration is invalid.
137 137
138 Pad-level image format configuration support c 138 Pad-level image format configuration support can be tested by calling
139 the :ref:`VIDIOC_SUBDEV_G_FMT` ioctl on pad 139 the :ref:`VIDIOC_SUBDEV_G_FMT` ioctl on pad
140 0. If the driver returns an ``EINVAL`` error c 140 0. If the driver returns an ``EINVAL`` error code pad-level format
141 configuration is not supported by the sub-devi 141 configuration is not supported by the sub-device.
142 142
143 143
144 Format Negotiation 144 Format Negotiation
145 ------------------ 145 ------------------
146 146
147 Acceptable formats on pads can (and usually do 147 Acceptable formats on pads can (and usually do) depend on a number of
148 external parameters, such as formats on other 148 external parameters, such as formats on other pads, active links, or
149 even controls. Finding a combination of format 149 even controls. Finding a combination of formats on all pads in a video
150 pipeline, acceptable to both application and d 150 pipeline, acceptable to both application and driver, can't rely on
151 formats enumeration only. A format negotiation 151 formats enumeration only. A format negotiation mechanism is required.
152 152
153 Central to the format negotiation mechanism ar 153 Central to the format negotiation mechanism are the get/set format
154 operations. When called with the ``which`` arg 154 operations. When called with the ``which`` argument set to
155 :ref:`V4L2_SUBDEV_FORMAT_TRY <VIDIOC_SUBDEV_G_ 155 :ref:`V4L2_SUBDEV_FORMAT_TRY <VIDIOC_SUBDEV_G_FMT>`, the
156 :ref:`VIDIOC_SUBDEV_G_FMT <VIDIOC_SUBDEV_G_FMT 156 :ref:`VIDIOC_SUBDEV_G_FMT <VIDIOC_SUBDEV_G_FMT>` and
157 :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT 157 :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctls operate on
158 a set of formats parameters that are not conne 158 a set of formats parameters that are not connected to the hardware
159 configuration. Modifying those 'try' formats l 159 configuration. Modifying those 'try' formats leaves the device state
160 untouched (this applies to both the software s 160 untouched (this applies to both the software state stored in the driver
161 and the hardware state stored in the device it 161 and the hardware state stored in the device itself).
162 162
163 While not kept as part of the device state, tr 163 While not kept as part of the device state, try formats are stored in
164 the sub-device file handles. A 164 the sub-device file handles. A
165 :ref:`VIDIOC_SUBDEV_G_FMT <VIDIOC_SUBDEV_G_FMT 165 :ref:`VIDIOC_SUBDEV_G_FMT <VIDIOC_SUBDEV_G_FMT>` call will return
166 the last try format set *on the same sub-devic 166 the last try format set *on the same sub-device file handle*. Several
167 applications querying the same sub-device at t 167 applications querying the same sub-device at the same time will thus not
168 interact with each other. 168 interact with each other.
169 169
170 To find out whether a particular format is sup 170 To find out whether a particular format is supported by the device,
171 applications use the 171 applications use the
172 :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT 172 :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctl. Drivers
173 verify and, if needed, change the requested `` 173 verify and, if needed, change the requested ``format`` based on device
174 requirements and return the possibly modified 174 requirements and return the possibly modified value. Applications can
175 then choose to try a different format or accep 175 then choose to try a different format or accept the returned value and
176 continue. 176 continue.
177 177
178 Formats returned by the driver during a negoti 178 Formats returned by the driver during a negotiation iteration are
179 guaranteed to be supported by the device. In p 179 guaranteed to be supported by the device. In particular, drivers
180 guarantee that a returned format will not be f 180 guarantee that a returned format will not be further changed if passed
181 to an :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV 181 to an :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` call as-is
182 (as long as external parameters, such as forma 182 (as long as external parameters, such as formats on other pads or links'
183 configuration are not changed). 183 configuration are not changed).
184 184
185 Drivers automatically propagate formats inside 185 Drivers automatically propagate formats inside sub-devices. When a try
186 or active format is set on a pad, correspondin 186 or active format is set on a pad, corresponding formats on other pads of
187 the same sub-device can be modified by the dri 187 the same sub-device can be modified by the driver. Drivers are free to
188 modify formats as required by the device. Howe 188 modify formats as required by the device. However, they should comply
189 with the following rules when possible: 189 with the following rules when possible:
190 190
191 - Formats should be propagated from sink pads 191 - Formats should be propagated from sink pads to source pads. Modifying
192 a format on a source pad should not modify 192 a format on a source pad should not modify the format on any sink
193 pad. 193 pad.
194 194
195 - Sub-devices that scale frames using variabl 195 - Sub-devices that scale frames using variable scaling factors should
196 reset the scale factors to default values w 196 reset the scale factors to default values when sink pads formats are
197 modified. If the 1:1 scaling ratio is suppo 197 modified. If the 1:1 scaling ratio is supported, this means that
198 source pads formats should be reset to the 198 source pads formats should be reset to the sink pads formats.
199 199
200 Formats are not propagated across links, as th 200 Formats are not propagated across links, as that would involve
201 propagating them from one sub-device file hand 201 propagating them from one sub-device file handle to another.
202 Applications must then take care to configure 202 Applications must then take care to configure both ends of every link
203 explicitly with compatible formats. Identical 203 explicitly with compatible formats. Identical formats on the two ends of
204 a link are guaranteed to be compatible. Driver 204 a link are guaranteed to be compatible. Drivers are free to accept
205 different formats matching device requirements 205 different formats matching device requirements as being compatible.
206 206
207 :ref:`sample-pipeline-config` shows a sample c 207 :ref:`sample-pipeline-config` shows a sample configuration sequence
208 for the pipeline described in :ref:`pipeline-s 208 for the pipeline described in :ref:`pipeline-scaling` (table columns
209 list entity names and pad numbers). 209 list entity names and pad numbers).
210 210
211 211
212 .. raw:: latex 212 .. raw:: latex
213 213
214 \begingroup 214 \begingroup
215 \scriptsize 215 \scriptsize
216 \setlength{\tabcolsep}{2pt} 216 \setlength{\tabcolsep}{2pt}
217 217
218 .. tabularcolumns:: |p{2.0cm}|p{2.1cm}|p{2.1cm 218 .. tabularcolumns:: |p{2.0cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|p{2.1cm}|
219 219
220 .. _sample-pipeline-config: 220 .. _sample-pipeline-config:
221 221
222 .. flat-table:: Sample Pipeline Configuration 222 .. flat-table:: Sample Pipeline Configuration
223 :header-rows: 1 223 :header-rows: 1
224 :stub-columns: 0 224 :stub-columns: 0
225 :widths: 5 5 5 5 5 5 5 225 :widths: 5 5 5 5 5 5 5
226 226
227 * - 227 * -
228 - Sensor/0 228 - Sensor/0
229 229
230 format 230 format
231 - Frontend/0 231 - Frontend/0
232 232
233 format 233 format
234 - Frontend/1 234 - Frontend/1
235 235
236 format 236 format
237 - Scaler/0 237 - Scaler/0
238 238
239 format 239 format
240 - Scaler/0 240 - Scaler/0
241 241
242 compose selection rectangle 242 compose selection rectangle
243 - Scaler/1 243 - Scaler/1
244 244
245 format 245 format
246 * - Initial state 246 * - Initial state
247 - 2048x1536 247 - 2048x1536
248 248
249 SGRBG8_1X8 249 SGRBG8_1X8
250 - (default) 250 - (default)
251 - (default) 251 - (default)
252 - (default) 252 - (default)
253 - (default) 253 - (default)
254 - (default) 254 - (default)
255 * - Configure frontend sink format 255 * - Configure frontend sink format
256 - 2048x1536 256 - 2048x1536
257 257
258 SGRBG8_1X8 258 SGRBG8_1X8
259 - *2048x1536* 259 - *2048x1536*
260 260
261 *SGRBG8_1X8* 261 *SGRBG8_1X8*
262 - *2046x1534* 262 - *2046x1534*
263 263
264 *SGRBG8_1X8* 264 *SGRBG8_1X8*
265 - (default) 265 - (default)
266 - (default) 266 - (default)
267 - (default) 267 - (default)
268 * - Configure scaler sink format 268 * - Configure scaler sink format
269 - 2048x1536 269 - 2048x1536
270 270
271 SGRBG8_1X8 271 SGRBG8_1X8
272 - 2048x1536 272 - 2048x1536
273 273
274 SGRBG8_1X8 274 SGRBG8_1X8
275 - 2046x1534 275 - 2046x1534
276 276
277 SGRBG8_1X8 277 SGRBG8_1X8
278 - *2046x1534* 278 - *2046x1534*
279 279
280 *SGRBG8_1X8* 280 *SGRBG8_1X8*
281 - *0,0/2046x1534* 281 - *0,0/2046x1534*
282 - *2046x1534* 282 - *2046x1534*
283 283
284 *SGRBG8_1X8* 284 *SGRBG8_1X8*
285 * - Configure scaler sink compose selectio 285 * - Configure scaler sink compose selection
286 - 2048x1536 286 - 2048x1536
287 287
288 SGRBG8_1X8 288 SGRBG8_1X8
289 - 2048x1536 289 - 2048x1536
290 290
291 SGRBG8_1X8 291 SGRBG8_1X8
292 - 2046x1534 292 - 2046x1534
293 293
294 SGRBG8_1X8 294 SGRBG8_1X8
295 - 2046x1534 295 - 2046x1534
296 296
297 SGRBG8_1X8 297 SGRBG8_1X8
298 - *0,0/1280x960* 298 - *0,0/1280x960*
299 - *1280x960* 299 - *1280x960*
300 300
301 *SGRBG8_1X8* 301 *SGRBG8_1X8*
302 302
303 .. raw:: latex 303 .. raw:: latex
304 304
305 \endgroup 305 \endgroup
306 306
307 1. Initial state. The sensor source pad format 307 1. Initial state. The sensor source pad format is set to its native 3MP
308 size and V4L2_MBUS_FMT_SGRBG8_1X8 media bus 308 size and V4L2_MBUS_FMT_SGRBG8_1X8 media bus code. Formats on the
309 host frontend and scaler sink and source pa 309 host frontend and scaler sink and source pads have the default
310 values, as well as the compose rectangle on 310 values, as well as the compose rectangle on the scaler's sink pad.
311 311
312 2. The application configures the frontend sin 312 2. The application configures the frontend sink pad format's size to
313 2048x1536 and its media bus code to V4L2_MB 313 2048x1536 and its media bus code to V4L2_MBUS_FMT_SGRBG_1X8. The
314 driver propagates the format to the fronten 314 driver propagates the format to the frontend source pad.
315 315
316 3. The application configures the scaler sink 316 3. The application configures the scaler sink pad format's size to
317 2046x1534 and the media bus code to V4L2_MB 317 2046x1534 and the media bus code to V4L2_MBUS_FMT_SGRBG_1X8 to
318 match the frontend source size and media bu 318 match the frontend source size and media bus code. The media bus code
319 on the sink pad is set to V4L2_MBUS_FMT_SGR 319 on the sink pad is set to V4L2_MBUS_FMT_SGRBG_1X8. The driver
320 propagates the size to the compose selectio 320 propagates the size to the compose selection rectangle on the
321 scaler's sink pad, and the format to the sc 321 scaler's sink pad, and the format to the scaler source pad.
322 322
323 4. The application configures the size of the 323 4. The application configures the size of the compose selection
324 rectangle of the scaler's sink pad 1280x960 324 rectangle of the scaler's sink pad 1280x960. The driver propagates
325 the size to the scaler's source pad format. 325 the size to the scaler's source pad format.
326 326
327 When satisfied with the try results, applicati 327 When satisfied with the try results, applications can set the active
328 formats by setting the ``which`` argument to 328 formats by setting the ``which`` argument to
329 ``V4L2_SUBDEV_FORMAT_ACTIVE``. Active formats 329 ``V4L2_SUBDEV_FORMAT_ACTIVE``. Active formats are changed exactly as try
330 formats by drivers. To avoid modifying the har 330 formats by drivers. To avoid modifying the hardware state during format
331 negotiation, applications should negotiate try 331 negotiation, applications should negotiate try formats first and then
332 modify the active settings using the try forma 332 modify the active settings using the try formats returned during the
333 last negotiation iteration. This guarantees th 333 last negotiation iteration. This guarantees that the active format will
334 be applied as-is by the driver without being m 334 be applied as-is by the driver without being modified.
335 335
336 336
337 .. _v4l2-subdev-selections: 337 .. _v4l2-subdev-selections:
338 338
339 Selections: cropping, scaling and composition 339 Selections: cropping, scaling and composition
340 --------------------------------------------- 340 ---------------------------------------------
341 341
342 Many sub-devices support cropping frames on th 342 Many sub-devices support cropping frames on their input or output pads
343 (or possible even on both). Cropping is used t 343 (or possible even on both). Cropping is used to select the area of
344 interest in an image, typically on an image se 344 interest in an image, typically on an image sensor or a video decoder.
345 It can also be used as part of digital zoom im 345 It can also be used as part of digital zoom implementations to select
346 the area of the image that will be scaled up. 346 the area of the image that will be scaled up.
347 347
348 Crop settings are defined by a crop rectangle 348 Crop settings are defined by a crop rectangle and represented in a
349 struct :c:type:`v4l2_rect` by the coordinates 349 struct :c:type:`v4l2_rect` by the coordinates of the top
350 left corner and the rectangle size. Both the c 350 left corner and the rectangle size. Both the coordinates and sizes are
351 expressed in pixels. 351 expressed in pixels.
352 352
353 As for pad formats, drivers store try and acti 353 As for pad formats, drivers store try and active rectangles for the
354 selection targets :ref:`v4l2-selections-common 354 selection targets :ref:`v4l2-selections-common`.
355 355
356 On sink pads, cropping is applied relative to 356 On sink pads, cropping is applied relative to the current pad format.
357 The pad format represents the image size as re 357 The pad format represents the image size as received by the sub-device
358 from the previous block in the pipeline, and t 358 from the previous block in the pipeline, and the crop rectangle
359 represents the sub-image that will be transmit 359 represents the sub-image that will be transmitted further inside the
360 sub-device for processing. 360 sub-device for processing.
361 361
362 The scaling operation changes the size of the 362 The scaling operation changes the size of the image by scaling it to new
363 dimensions. The scaling ratio isn't specified 363 dimensions. The scaling ratio isn't specified explicitly, but is implied
364 from the original and scaled image sizes. Both 364 from the original and scaled image sizes. Both sizes are represented by
365 struct :c:type:`v4l2_rect`. 365 struct :c:type:`v4l2_rect`.
366 366
367 Scaling support is optional. When supported by 367 Scaling support is optional. When supported by a subdev, the crop
368 rectangle on the subdev's sink pad is scaled t 368 rectangle on the subdev's sink pad is scaled to the size configured
369 using the 369 using the
370 :ref:`VIDIOC_SUBDEV_S_SELECTION <VIDIOC_SUBDEV 370 :ref:`VIDIOC_SUBDEV_S_SELECTION <VIDIOC_SUBDEV_G_SELECTION>` IOCTL
371 using ``V4L2_SEL_TGT_COMPOSE`` selection targe 371 using ``V4L2_SEL_TGT_COMPOSE`` selection target on the same pad. If the
372 subdev supports scaling but not composing, the 372 subdev supports scaling but not composing, the top and left values are
373 not used and must always be set to zero. 373 not used and must always be set to zero.
374 374
375 On source pads, cropping is similar to sink pa 375 On source pads, cropping is similar to sink pads, with the exception
376 that the source size from which the cropping i 376 that the source size from which the cropping is performed, is the
377 COMPOSE rectangle on the sink pad. In both sin 377 COMPOSE rectangle on the sink pad. In both sink and source pads, the
378 crop rectangle must be entirely contained insi 378 crop rectangle must be entirely contained inside the source image size
379 for the crop operation. 379 for the crop operation.
380 380
381 The drivers should always use the closest poss 381 The drivers should always use the closest possible rectangle the user
382 requests on all selection targets, unless spec 382 requests on all selection targets, unless specifically told otherwise.
383 ``V4L2_SEL_FLAG_GE`` and ``V4L2_SEL_FLAG_LE`` 383 ``V4L2_SEL_FLAG_GE`` and ``V4L2_SEL_FLAG_LE`` flags may be used to round
384 the image size either up or down. :ref:`v4l2-s 384 the image size either up or down. :ref:`v4l2-selection-flags`
385 385
386 386
387 Types of selection targets 387 Types of selection targets
388 -------------------------- 388 --------------------------
389 389
390 390
391 Actual targets 391 Actual targets
392 ^^^^^^^^^^^^^^ 392 ^^^^^^^^^^^^^^
393 393
394 Actual targets (without a postfix) reflect the 394 Actual targets (without a postfix) reflect the actual hardware
395 configuration at any point of time. There is a 395 configuration at any point of time. There is a BOUNDS target
396 corresponding to every actual target. 396 corresponding to every actual target.
397 397
398 398
399 BOUNDS targets 399 BOUNDS targets
400 ^^^^^^^^^^^^^^ 400 ^^^^^^^^^^^^^^
401 401
402 BOUNDS targets is the smallest rectangle that 402 BOUNDS targets is the smallest rectangle that contains all valid actual
403 rectangles. It may not be possible to set the 403 rectangles. It may not be possible to set the actual rectangle as large
404 as the BOUNDS rectangle, however. This may be 404 as the BOUNDS rectangle, however. This may be because e.g. a sensor's
405 pixel array is not rectangular but cross-shape 405 pixel array is not rectangular but cross-shaped or round. The maximum
406 size may also be smaller than the BOUNDS recta 406 size may also be smaller than the BOUNDS rectangle.
407 407
408 408
409 .. _format-propagation: 409 .. _format-propagation:
410 410
411 Order of configuration and format propagation 411 Order of configuration and format propagation
412 --------------------------------------------- 412 ---------------------------------------------
413 413
414 Inside subdevs, the order of image processing 414 Inside subdevs, the order of image processing steps will always be from
415 the sink pad towards the source pad. This is a 415 the sink pad towards the source pad. This is also reflected in the order
416 in which the configuration must be performed b 416 in which the configuration must be performed by the user: the changes
417 made will be propagated to any subsequent stag 417 made will be propagated to any subsequent stages. If this behaviour is
418 not desired, the user must set ``V4L2_SEL_FLAG 418 not desired, the user must set ``V4L2_SEL_FLAG_KEEP_CONFIG`` flag. This
419 flag causes no propagation of the changes are 419 flag causes no propagation of the changes are allowed in any
420 circumstances. This may also cause the accesse 420 circumstances. This may also cause the accessed rectangle to be adjusted
421 by the driver, depending on the properties of 421 by the driver, depending on the properties of the underlying hardware.
422 422
423 The coordinates to a step always refer to the 423 The coordinates to a step always refer to the actual size of the
424 previous step. The exception to this rule is t 424 previous step. The exception to this rule is the sink compose
425 rectangle, which refers to the sink compose bo 425 rectangle, which refers to the sink compose bounds rectangle --- if it
426 is supported by the hardware. 426 is supported by the hardware.
427 427
428 1. Sink pad format. The user configures the si 428 1. Sink pad format. The user configures the sink pad format. This format
429 defines the parameters of the image the ent 429 defines the parameters of the image the entity receives through the
430 pad for further processing. 430 pad for further processing.
431 431
432 2. Sink pad actual crop selection. The sink pa 432 2. Sink pad actual crop selection. The sink pad crop defines the crop
433 performed to the sink pad format. 433 performed to the sink pad format.
434 434
435 3. Sink pad actual compose selection. The size 435 3. Sink pad actual compose selection. The size of the sink pad compose
436 rectangle defines the scaling ratio compare 436 rectangle defines the scaling ratio compared to the size of the sink
437 pad crop rectangle. The location of the com 437 pad crop rectangle. The location of the compose rectangle specifies
438 the location of the actual sink compose rec 438 the location of the actual sink compose rectangle in the sink compose
439 bounds rectangle. 439 bounds rectangle.
440 440
441 4. Source pad actual crop selection. Crop on t 441 4. Source pad actual crop selection. Crop on the source pad defines crop
442 performed to the image in the sink compose 442 performed to the image in the sink compose bounds rectangle.
443 443
444 5. Source pad format. The source pad format de 444 5. Source pad format. The source pad format defines the output pixel
445 format of the subdev, as well as the other 445 format of the subdev, as well as the other parameters with the
446 exception of the image width and height. Wi 446 exception of the image width and height. Width and height are defined
447 by the size of the source pad actual crop s 447 by the size of the source pad actual crop selection.
448 448
449 Accessing any of the above rectangles not supp 449 Accessing any of the above rectangles not supported by the subdev will
450 return ``EINVAL``. Any rectangle referring to 450 return ``EINVAL``. Any rectangle referring to a previous unsupported
451 rectangle coordinates will instead refer to th 451 rectangle coordinates will instead refer to the previous supported
452 rectangle. For example, if sink crop is not su 452 rectangle. For example, if sink crop is not supported, the compose
453 selection will refer to the sink pad format di 453 selection will refer to the sink pad format dimensions instead.
454 454
455 455
456 .. _subdev-image-processing-crop: 456 .. _subdev-image-processing-crop:
457 457
458 .. kernel-figure:: subdev-image-processing-cro 458 .. kernel-figure:: subdev-image-processing-crop.svg
459 :alt: subdev-image-processing-crop.svg 459 :alt: subdev-image-processing-crop.svg
460 :align: center 460 :align: center
461 461
462 **Figure 4.5. Image processing in subdevs: 462 **Figure 4.5. Image processing in subdevs: simple crop example**
463 463
464 In the above example, the subdev supports crop 464 In the above example, the subdev supports cropping on its sink pad. To
465 configure it, the user sets the media bus form 465 configure it, the user sets the media bus format on the subdev's sink
466 pad. Now the actual crop rectangle can be set 466 pad. Now the actual crop rectangle can be set on the sink pad --- the
467 location and size of this rectangle reflect th 467 location and size of this rectangle reflect the location and size of a
468 rectangle to be cropped from the sink format. 468 rectangle to be cropped from the sink format. The size of the sink crop
469 rectangle will also be the size of the format 469 rectangle will also be the size of the format of the subdev's source
470 pad. 470 pad.
471 471
472 472
473 .. _subdev-image-processing-scaling-multi-sour 473 .. _subdev-image-processing-scaling-multi-source:
474 474
475 .. kernel-figure:: subdev-image-processing-sca 475 .. kernel-figure:: subdev-image-processing-scaling-multi-source.svg
476 :alt: subdev-image-processing-scaling-mu 476 :alt: subdev-image-processing-scaling-multi-source.svg
477 :align: center 477 :align: center
478 478
479 **Figure 4.6. Image processing in subdevs: 479 **Figure 4.6. Image processing in subdevs: scaling with multiple sources**
480 480
481 In this example, the subdev is capable of firs 481 In this example, the subdev is capable of first cropping, then scaling
482 and finally cropping for two source pads indiv 482 and finally cropping for two source pads individually from the resulting
483 scaled image. The location of the scaled image 483 scaled image. The location of the scaled image in the cropped image is
484 ignored in sink compose target. Both of the lo 484 ignored in sink compose target. Both of the locations of the source crop
485 rectangles refer to the sink scaling rectangle 485 rectangles refer to the sink scaling rectangle, independently cropping
486 an area at location specified by the source cr 486 an area at location specified by the source crop rectangle from it.
487 487
488 488
489 .. _subdev-image-processing-full: 489 .. _subdev-image-processing-full:
490 490
491 .. kernel-figure:: subdev-image-processing-ful 491 .. kernel-figure:: subdev-image-processing-full.svg
492 :alt: subdev-image-processing-full.svg 492 :alt: subdev-image-processing-full.svg
493 :align: center 493 :align: center
494 494
495 **Figure 4.7. Image processing in subdevs: 495 **Figure 4.7. Image processing in subdevs: scaling and composition with multiple sinks and sources**
496 496
497 The subdev driver supports two sink pads and t 497 The subdev driver supports two sink pads and two source pads. The images
498 from both of the sink pads are individually cr 498 from both of the sink pads are individually cropped, then scaled and
499 further composed on the composition bounds rec 499 further composed on the composition bounds rectangle. From that, two
500 independent streams are cropped and sent out o 500 independent streams are cropped and sent out of the subdev from the
501 source pads. 501 source pads.
502 502
503 503
504 .. toctree:: 504 .. toctree::
505 :maxdepth: 1 505 :maxdepth: 1
506 506
507 subdev-formats 507 subdev-formats
508 508
509 .. _subdev-routing: 509 .. _subdev-routing:
510 510
511 Streams, multiplexed media pads and internal r 511 Streams, multiplexed media pads and internal routing
512 ---------------------------------------------- 512 ----------------------------------------------------
513 513
514 Simple V4L2 sub-devices do not support multipl 514 Simple V4L2 sub-devices do not support multiple, unrelated video streams,
515 and only a single stream can pass through a me 515 and only a single stream can pass through a media link and a media pad.
516 Thus each pad contains a format and selection 516 Thus each pad contains a format and selection configuration for that
517 single stream. A subdev can do stream processi 517 single stream. A subdev can do stream processing and split a stream into
518 two or compose two streams into one, but the i 518 two or compose two streams into one, but the inputs and outputs for the
519 subdev are still a single stream per pad. 519 subdev are still a single stream per pad.
520 520
521 Some hardware, e.g. MIPI CSI-2, support multip 521 Some hardware, e.g. MIPI CSI-2, support multiplexed streams, that is, multiple
522 data streams are transmitted on the same bus, 522 data streams are transmitted on the same bus, which is represented by a media
523 link connecting a transmitter source pad with 523 link connecting a transmitter source pad with a sink pad on the receiver. For
524 example, a camera sensor can produce two disti 524 example, a camera sensor can produce two distinct streams, a pixel stream and a
525 metadata stream, which are transmitted on the 525 metadata stream, which are transmitted on the multiplexed data bus, represented
526 by a media link which connects the single sens 526 by a media link which connects the single sensor's source pad with the receiver
527 sink pad. The stream-aware receiver will de-mu 527 sink pad. The stream-aware receiver will de-multiplex the streams received on
528 the its sink pad and allows to route them indi 528 the its sink pad and allows to route them individually to one of its source
529 pads. 529 pads.
530 530
531 Subdevice drivers that support multiplexed str 531 Subdevice drivers that support multiplexed streams are compatible with
532 non-multiplexed subdev drivers. However, if th 532 non-multiplexed subdev drivers. However, if the driver at the sink end of a link
533 does not support streams, then only stream 0 o 533 does not support streams, then only stream 0 of source end may be captured.
534 There may be additional limitations specific t 534 There may be additional limitations specific to the sink device.
535 535
536 Understanding streams 536 Understanding streams
537 ^^^^^^^^^^^^^^^^^^^^^ 537 ^^^^^^^^^^^^^^^^^^^^^
538 538
539 A stream is a stream of content (e.g. pixel da 539 A stream is a stream of content (e.g. pixel data or metadata) flowing through
540 the media pipeline from a source (e.g. a senso 540 the media pipeline from a source (e.g. a sensor) towards the final sink (e.g. a
541 receiver and demultiplexer in a SoC). Each med 541 receiver and demultiplexer in a SoC). Each media link carries all the enabled
542 streams from one end of the link to the other, 542 streams from one end of the link to the other, and sub-devices have routing
543 tables which describe how the incoming streams 543 tables which describe how the incoming streams from sink pads are routed to the
544 source pads. 544 source pads.
545 545
546 A stream ID is a media pad-local identifier fo 546 A stream ID is a media pad-local identifier for a stream. Streams IDs of
547 the same stream must be equal on both ends of 547 the same stream must be equal on both ends of a link. In other words,
548 a particular stream ID must exist on both side 548 a particular stream ID must exist on both sides of a media
549 link, but another stream ID can be used for th 549 link, but another stream ID can be used for the same stream at the other side
550 of the sub-device. 550 of the sub-device.
551 551
552 A stream at a specific point in the media pipe 552 A stream at a specific point in the media pipeline is identified by the
553 sub-device and a (pad, stream) pair. For sub-d 553 sub-device and a (pad, stream) pair. For sub-devices that do not support
554 multiplexed streams the 'stream' field is alwa 554 multiplexed streams the 'stream' field is always 0.
555 555
556 Interaction between routes, streams, formats a 556 Interaction between routes, streams, formats and selections
557 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 557 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
558 558
559 The addition of streams to the V4L2 sub-device 559 The addition of streams to the V4L2 sub-device interface moves the sub-device
560 formats and selections from pads to (pad, stre 560 formats and selections from pads to (pad, stream) pairs. Besides the
561 usual pad, also the stream ID needs to be prov 561 usual pad, also the stream ID needs to be provided for setting formats and
562 selections. The order of configuring formats a 562 selections. The order of configuring formats and selections along a stream is
563 the same as without streams (see :ref:`format- 563 the same as without streams (see :ref:`format-propagation`).
564 564
565 Instead of the sub-device wide merging of stre 565 Instead of the sub-device wide merging of streams from all sink pads
566 towards all source pads, data flows for each r 566 towards all source pads, data flows for each route are separate from each
567 other. Any number of routes from streams on si 567 other. Any number of routes from streams on sink pads towards streams on
568 source pads is allowed, to the extent supporte 568 source pads is allowed, to the extent supported by drivers. For every
569 stream on a source pad, however, only a single 569 stream on a source pad, however, only a single route is allowed.
570 570
571 Any configurations of a stream within a pad, s 571 Any configurations of a stream within a pad, such as format or selections,
572 are independent of similar configurations on o 572 are independent of similar configurations on other streams. This is
573 subject to change in the future. 573 subject to change in the future.
574 574
575 Device types and routing setup 575 Device types and routing setup
576 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 576 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
577 577
578 Different kinds of sub-devices have differing 578 Different kinds of sub-devices have differing behaviour for route activation,
579 depending on the hardware. In all cases, howev 579 depending on the hardware. In all cases, however, only routes that have the
580 ``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set are 580 ``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set are active.
581 581
582 Devices generating the streams may allow enabl 582 Devices generating the streams may allow enabling and disabling some of the
583 routes or have a fixed routing configuration. 583 routes or have a fixed routing configuration. If the routes can be disabled, not
584 declaring the routes (or declaring them withou 584 declaring the routes (or declaring them without
585 ``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set) in 585 ``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set) in ``VIDIOC_SUBDEV_S_ROUTING`` will
586 disable the routes. ``VIDIOC_SUBDEV_S_ROUTING` 586 disable the routes. ``VIDIOC_SUBDEV_S_ROUTING`` will still return such routes
587 back to the user in the routes array, with the 587 back to the user in the routes array, with the ``V4L2_SUBDEV_STREAM_FL_ACTIVE``
588 flag unset. 588 flag unset.
589 589
590 Devices transporting the streams almost always 590 Devices transporting the streams almost always have more configurability with
591 respect to routing. Typically any route betwee 591 respect to routing. Typically any route between the sub-device's sink and source
592 pads is possible, and multiple routes (usually 592 pads is possible, and multiple routes (usually up to certain limited number) may
593 be active simultaneously. For such devices, no 593 be active simultaneously. For such devices, no routes are created by the driver
594 and user-created routes are fully replaced whe 594 and user-created routes are fully replaced when ``VIDIOC_SUBDEV_S_ROUTING`` is
595 called on the sub-device. Such newly created r 595 called on the sub-device. Such newly created routes have the device's default
596 configuration for format and selection rectang 596 configuration for format and selection rectangles.
597 597
598 Configuring streams 598 Configuring streams
599 ^^^^^^^^^^^^^^^^^^^ 599 ^^^^^^^^^^^^^^^^^^^
600 600
601 The configuration of the streams is done indiv 601 The configuration of the streams is done individually for each sub-device and
602 the validity of the streams between sub-device 602 the validity of the streams between sub-devices is validated when the pipeline
603 is started. 603 is started.
604 604
605 There are three steps in configuring the strea 605 There are three steps in configuring the streams:
606 606
607 1. Set up links. Connect the pads between sub- 607 1. Set up links. Connect the pads between sub-devices using the
608 :ref:`Media Controller API <media_controlle 608 :ref:`Media Controller API <media_controller>`
609 609
610 2. Streams. Streams are declared and their rou 610 2. Streams. Streams are declared and their routing is configured by setting the
611 routing table for the sub-device using :ref 611 routing table for the sub-device using :ref:`VIDIOC_SUBDEV_S_ROUTING
612 <VIDIOC_SUBDEV_G_ROUTING>` ioctl. Note that 612 <VIDIOC_SUBDEV_G_ROUTING>` ioctl. Note that setting the routing table will
613 reset formats and selections in the sub-dev 613 reset formats and selections in the sub-device to default values.
614 614
615 3. Configure formats and selections. Formats a 615 3. Configure formats and selections. Formats and selections of each stream are
616 configured separately as documented for pla 616 configured separately as documented for plain sub-devices in
617 :ref:`format-propagation`. The stream ID is 617 :ref:`format-propagation`. The stream ID is set to the same stream ID
618 associated with either sink or source pads 618 associated with either sink or source pads of routes configured using the
619 :ref:`VIDIOC_SUBDEV_S_ROUTING <VIDIOC_SUBDE 619 :ref:`VIDIOC_SUBDEV_S_ROUTING <VIDIOC_SUBDEV_G_ROUTING>` ioctl.
620 620
621 Multiplexed streams setup example 621 Multiplexed streams setup example
622 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 622 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
623 623
624 A simple example of a multiplexed stream setup 624 A simple example of a multiplexed stream setup might be as follows:
625 625
626 - Two identical sensors (Sensor A and Sensor B 626 - Two identical sensors (Sensor A and Sensor B). Each sensor has a single source
627 pad (pad 0) which carries a pixel data strea 627 pad (pad 0) which carries a pixel data stream.
628 628
629 - Multiplexer bridge (Bridge). The bridge has 629 - Multiplexer bridge (Bridge). The bridge has two sink pads, connected to the
630 sensors (pads 0, 1), and one source pad (pad 630 sensors (pads 0, 1), and one source pad (pad 2), which outputs two streams.
631 631
632 - Receiver in the SoC (Receiver). The receiver 632 - Receiver in the SoC (Receiver). The receiver has a single sink pad (pad 0),
633 connected to the bridge, and two source pads 633 connected to the bridge, and two source pads (pads 1-2), going to the DMA
634 engine. The receiver demultiplexes the incom 634 engine. The receiver demultiplexes the incoming streams to the source pads.
635 635
636 - DMA Engines in the SoC (DMA Engine), one for 636 - DMA Engines in the SoC (DMA Engine), one for each stream. Each DMA engine is
637 connected to a single source pad in the rece 637 connected to a single source pad in the receiver.
638 638
639 The sensors, the bridge and the receiver are m 639 The sensors, the bridge and the receiver are modeled as V4L2 sub-devices,
640 exposed to userspace via /dev/v4l-subdevX devi 640 exposed to userspace via /dev/v4l-subdevX device nodes. The DMA engines are
641 modeled as V4L2 devices, exposed to userspace 641 modeled as V4L2 devices, exposed to userspace via /dev/videoX nodes.
642 642
643 To configure this pipeline, the userspace must 643 To configure this pipeline, the userspace must take the following steps:
644 644
645 1. Set up media links between entities: connec 645 1. Set up media links between entities: connect the sensors to the bridge,
646 bridge to the receiver, and the receiver to 646 bridge to the receiver, and the receiver to the DMA engines. This step does
647 not differ from normal non-multiplexed medi 647 not differ from normal non-multiplexed media controller setup.
648 648
649 2. Configure routing 649 2. Configure routing
650 650
651 .. flat-table:: Bridge routing table 651 .. flat-table:: Bridge routing table
652 :header-rows: 1 652 :header-rows: 1
653 653
654 * - Sink Pad/Stream 654 * - Sink Pad/Stream
655 - Source Pad/Stream 655 - Source Pad/Stream
656 - Routing Flags 656 - Routing Flags
657 - Comments 657 - Comments
658 * - 0/0 658 * - 0/0
659 - 2/0 659 - 2/0
660 - V4L2_SUBDEV_ROUTE_FL_ACTIVE 660 - V4L2_SUBDEV_ROUTE_FL_ACTIVE
661 - Pixel data stream from Sensor A 661 - Pixel data stream from Sensor A
662 * - 1/0 662 * - 1/0
663 - 2/1 663 - 2/1
664 - V4L2_SUBDEV_ROUTE_FL_ACTIVE 664 - V4L2_SUBDEV_ROUTE_FL_ACTIVE
665 - Pixel data stream from Sensor B 665 - Pixel data stream from Sensor B
666 666
667 .. flat-table:: Receiver routing table 667 .. flat-table:: Receiver routing table
668 :header-rows: 1 668 :header-rows: 1
669 669
670 * - Sink Pad/Stream 670 * - Sink Pad/Stream
671 - Source Pad/Stream 671 - Source Pad/Stream
672 - Routing Flags 672 - Routing Flags
673 - Comments 673 - Comments
674 * - 0/0 674 * - 0/0
675 - 1/0 675 - 1/0
676 - V4L2_SUBDEV_ROUTE_FL_ACTIVE 676 - V4L2_SUBDEV_ROUTE_FL_ACTIVE
677 - Pixel data stream from Sensor A 677 - Pixel data stream from Sensor A
678 * - 0/1 678 * - 0/1
679 - 2/0 679 - 2/0
680 - V4L2_SUBDEV_ROUTE_FL_ACTIVE 680 - V4L2_SUBDEV_ROUTE_FL_ACTIVE
681 - Pixel data stream from Sensor B 681 - Pixel data stream from Sensor B
682 682
683 3. Configure formats and selections 683 3. Configure formats and selections
684 684
685 After configuring routing, the next step is 685 After configuring routing, the next step is configuring the formats and
686 selections for the streams. This is similar 686 selections for the streams. This is similar to performing this step without
687 streams, with just one exception: the ``str 687 streams, with just one exception: the ``stream`` field needs to be assigned
688 to the value of the stream ID. 688 to the value of the stream ID.
689 689
690 A common way to accomplish this is to start 690 A common way to accomplish this is to start from the sensors and propagate
691 the configurations along the stream towards 691 the configurations along the stream towards the receiver, using
692 :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_ 692 :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctls to configure each
693 stream endpoint in each sub-device. 693 stream endpoint in each sub-device.
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