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Linux/Documentation/userspace-api/media/v4l/dev-subdev.rst

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Diff markup

Differences between /Documentation/userspace-api/media/v4l/dev-subdev.rst (Version linux-6.12-rc7) and /Documentation/userspace-api/media/v4l/dev-subdev.rst (Version linux-5.17.15)


  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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