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