Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml

   1 <refentry id="vidioc-g-ext-ctrls">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
   4 VIDIOC_TRY_EXT_CTRLS</refentrytitle>
   5     &manvol;
   6   </refmeta>
   7
   8   <refnamediv>
   9     <refname>VIDIOC_G_EXT_CTRLS</refname>
  10     <refname>VIDIOC_S_EXT_CTRLS</refname>
  11     <refname>VIDIOC_TRY_EXT_CTRLS</refname>
  12     <refpurpose>Get or set the value of several controls, try control
  13 values</refpurpose>
  14   </refnamediv>
  15
  16   <refsynopsisdiv>
  17     <funcsynopsis>
  18       <funcprototype>
  19         <funcdef>int <function>ioctl</function></funcdef>
  20         <paramdef>int <parameter>fd</parameter></paramdef>
  21         <paramdef>int <parameter>request</parameter></paramdef>
  22         <paramdef>struct v4l2_ext_controls
  23 *<parameter>argp</parameter></paramdef>
  24       </funcprototype>
  25     </funcsynopsis>
  26   </refsynopsisdiv>
  27
  28   <refsect1>
  29     <title>Arguments</title>
  30
  31     <variablelist>
  32       <varlistentry>
  33         <term><parameter>fd</parameter></term>
  34         <listitem>
  35           <para>&fd;</para>
  36         </listitem>
  37       </varlistentry>
  38       <varlistentry>
  39         <term><parameter>request</parameter></term>
  40         <listitem>
  41           <para>VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
  42 VIDIOC_TRY_EXT_CTRLS</para>
  43         </listitem>
  44       </varlistentry>
  45       <varlistentry>
  46         <term><parameter>argp</parameter></term>
  47         <listitem>
  48           <para></para>
  49         </listitem>
  50       </varlistentry>
  51     </variablelist>
  52   </refsect1>
  53
  54   <refsect1>
  55     <title>Description</title>
  56
  57     <para>These ioctls allow the caller to get or set multiple
  58 controls atomically. Control IDs are grouped into control classes (see
  59 <xref linkend="ctrl-class" />) and all controls in the control array
  60 must belong to the same control class.</para>
  61
  62     <para>Applications must always fill in the
  63 <structfield>count</structfield>,
  64 <structfield>which</structfield>,
  65 <structfield>controls</structfield> and
  66 <structfield>reserved</structfield> fields of &v4l2-ext-controls;, and
  67 initialize the &v4l2-ext-control; array pointed to by the
  68 <structfield>controls</structfield> fields.</para>
  69
  70     <para>To get the current value of a set of controls applications
  71 initialize the <structfield>id</structfield>,
  72 <structfield>size</structfield> and <structfield>reserved2</structfield> fields
  73 of each &v4l2-ext-control; and call the
  74 <constant>VIDIOC_G_EXT_CTRLS</constant> ioctl. String controls controls
  75 must also set the <structfield>string</structfield> field. Controls
  76 of compound types (<constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant> is set)
  77 must set the <structfield>ptr</structfield> field.</para>
  78
  79     <para>If the <structfield>size</structfield> is too small to
  80 receive the control result (only relevant for pointer-type controls
  81 like strings), then the driver will set <structfield>size</structfield>
  82 to a valid value and return an &ENOSPC;. You should re-allocate the
  83 memory to this new size and try again. For the string type it is possible that
  84 the same issue occurs again if the string has grown in the meantime. It is
  85 recommended to call &VIDIOC-QUERYCTRL; first and use
  86 <structfield>maximum</structfield>+1 as the new <structfield>size</structfield>
  87 value. It is guaranteed that that is sufficient memory.
  88 </para>
  89
  90     <para>N-dimensional arrays are set and retrieved row-by-row. You cannot set a partial
  91 array, all elements have to be set or retrieved. The total size is calculated
  92 as <structfield>elems</structfield> * <structfield>elem_size</structfield>.
  93 These values can be obtained by calling &VIDIOC-QUERY-EXT-CTRL;.</para>
  94
  95     <para>To change the value of a set of controls applications
  96 initialize the <structfield>id</structfield>, <structfield>size</structfield>,
  97 <structfield>reserved2</structfield> and
  98 <structfield>value/value64/string/ptr</structfield> fields of each &v4l2-ext-control; and
  99 call the <constant>VIDIOC_S_EXT_CTRLS</constant> ioctl. The controls
 100 will only be set if <emphasis>all</emphasis> control values are
 101 valid.</para>
 102
 103     <para>To check if a set of controls have correct values applications
 104 initialize the <structfield>id</structfield>, <structfield>size</structfield>,
 105 <structfield>reserved2</structfield> and
 106 <structfield>value/value64/string/ptr</structfield> fields of each &v4l2-ext-control; and
 107 call the <constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctl. It is up to
 108 the driver whether wrong values are automatically adjusted to a valid
 109 value or if an error is returned.</para>
 110
 111     <para>When the <structfield>id</structfield> or
 112 <structfield>which</structfield> is invalid drivers return an
 113 &EINVAL;. When the value is out of bounds drivers can choose to take
 114 the closest valid value or return an &ERANGE;, whatever seems more
 115 appropriate. In the first case the new value is set in
 116 &v4l2-ext-control;. If the new control value is inappropriate (e.g. the
 117 given menu index is not supported by the menu control), then this will
 118 also result in an &EINVAL; error.</para>
 119
 120     <para>The driver will only set/get these controls if all control
 121 values are correct. This prevents the situation where only some of the
 122 controls were set/get. Only low-level errors (&eg; a failed i2c
 123 command) can still cause this situation.</para>
 124
 125     <table pgwide="1" frame="none" id="v4l2-ext-control">
 126       <title>struct <structname>v4l2_ext_control</structname></title>
 127       <tgroup cols="4">
 128         &cs-ustr;
 129         <tbody valign="top">
 130           <row>
 131             <entry>__u32</entry>
 132             <entry><structfield>id</structfield></entry>
 133             <entry></entry>
 134             <entry>Identifies the control, set by the
 135 application.</entry>
 136           </row>
 137           <row>
 138             <entry>__u32</entry>
 139             <entry><structfield>size</structfield></entry>
 140             <entry></entry>
 141             <entry>The total size in bytes of the payload of this
 142 control. This is normally 0, but for pointer controls this should be
 143 set to the size of the memory containing the payload, or that will
 144 receive the payload. If <constant>VIDIOC_G_EXT_CTRLS</constant> finds
 145 that this value is less than is required to store
 146 the payload result, then it is set to a value large enough to store the
 147 payload result and ENOSPC is returned. Note that for string controls
 148 this <structfield>size</structfield> field should not be confused with the length of the string.
 149 This field refers to the size of the memory that contains the string.
 150 The actual <emphasis>length</emphasis> of the string may well be much smaller.
 151 </entry>
 152           </row>
 153           <row>
 154             <entry>__u32</entry>
 155             <entry><structfield>reserved2</structfield>[1]</entry>
 156             <entry></entry>
 157             <entry>Reserved for future extensions. Drivers and
 158 applications must set the array to zero.</entry>
 159           </row>
 160           <row>
 161             <entry>union</entry>
 162             <entry>(anonymous)</entry>
 163           </row>
 164           <row>
 165             <entry></entry>
 166             <entry>__s32</entry>
 167             <entry><structfield>value</structfield></entry>
 168             <entry>New value or current value. Valid if this control is not of
 169 type <constant>V4L2_CTRL_TYPE_INTEGER64</constant> and
 170 <constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant> is not set.</entry>
 171           </row>
 172           <row>
 173             <entry></entry>
 174             <entry>__s64</entry>
 175             <entry><structfield>value64</structfield></entry>
 176             <entry>New value or current value. Valid if this control is of
 177 type <constant>V4L2_CTRL_TYPE_INTEGER64</constant> and
 178 <constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant> is not set.</entry>
 179           </row>
 180           <row>
 181             <entry></entry>
 182             <entry>char *</entry>
 183             <entry><structfield>string</structfield></entry>
 184             <entry>A pointer to a string. Valid if this control is of
 185 type <constant>V4L2_CTRL_TYPE_STRING</constant>.</entry>
 186           </row>
 187           <row>
 188             <entry></entry>
 189             <entry>__u8 *</entry>
 190             <entry><structfield>p_u8</structfield></entry>
 191             <entry>A pointer to a matrix control of unsigned 8-bit values.
 192 Valid if this control is of type <constant>V4L2_CTRL_TYPE_U8</constant>.</entry>
 193           </row>
 194           <row>
 195             <entry></entry>
 196             <entry>__u16 *</entry>
 197             <entry><structfield>p_u16</structfield></entry>
 198             <entry>A pointer to a matrix control of unsigned 16-bit values.
 199 Valid if this control is of type <constant>V4L2_CTRL_TYPE_U16</constant>.</entry>
 200           </row>
 201           <row>
 202             <entry></entry>
 203             <entry>__u32 *</entry>
 204             <entry><structfield>p_u32</structfield></entry>
 205             <entry>A pointer to a matrix control of unsigned 32-bit values.
 206 Valid if this control is of type <constant>V4L2_CTRL_TYPE_U32</constant>.</entry>
 207           </row>
 208           <row>
 209             <entry></entry>
 210             <entry>void *</entry>
 211             <entry><structfield>ptr</structfield></entry>
 212             <entry>A pointer to a compound type which can be an N-dimensional array and/or a
 213 compound type (the control's type is >= <constant>V4L2_CTRL_COMPOUND_TYPES</constant>).
 214 Valid if <constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant> is set for this control.
 215 </entry>
 216           </row>
 217         </tbody>
 218       </tgroup>
 219     </table>
 220
 221     <table pgwide="1" frame="none" id="v4l2-ext-controls">
 222       <title>struct <structname>v4l2_ext_controls</structname></title>
 223       <tgroup cols="3">
 224         &cs-str;
 225         <tbody valign="top">
 226          <row>
 227             <entry>union</entry>
 228             <entry>(anonymous)</entry>
 229           </row>
 230           <row>
 231             <entry></entry>
 232             <entry>__u32</entry>
 233             <entry><structfield>ctrl_class</structfield></entry>
 234             <entry>The control class to which all controls belong, see
 235 <xref linkend="ctrl-class" />. Drivers that use a kernel framework for handling
 236 controls will also accept a value of 0 here, meaning that the controls can
 237 belong to any control class. Whether drivers support this can be tested by setting
 238 <structfield>ctrl_class</structfield> to 0 and calling <constant>VIDIOC_TRY_EXT_CTRLS</constant>
 239 with a <structfield>count</structfield> of 0. If that succeeds, then the driver
 240 supports this feature.</entry>
 241           </row>
 242           <row>
 243             <entry></entry>
 244             <entry>__u32</entry>
 245             <entry><structfield>which</structfield></entry>
 246             <entry><para>Which value of the control to get/set/try. <constant>V4L2_CTRL_WHICH_CUR_VAL</constant>
 247 will return the current value of the control and <constant>V4L2_CTRL_WHICH_DEF_VAL</constant> will
 248 return the default value of the control. Please note that you can only get the default value of the
 249 control, you cannot set or try it.</para>
 250 <para>For backwards compatibility you can also use a control class here (see
 251 <xref linkend="ctrl-class" />). In that case all controls have to belong to that
 252 control class. This usage is deprecated, instead just use <constant>V4L2_CTRL_WHICH_CUR_VAL</constant>.
 253 There are some very old drivers that do not yet support <constant>V4L2_CTRL_WHICH_CUR_VAL</constant>
 254 and that require a control class here. You can test for such drivers by setting ctrl_class to
 255 <constant>V4L2_CTRL_WHICH_CUR_VAL</constant> and calling VIDIOC_TRY_EXT_CTRLS with a count of 0.
 256 If that fails, then the driver does not support <constant>V4L2_CTRL_WHICH_CUR_VAL</constant>.</para>
 257 </entry>
 258           </row>
 259           <row>
 260             <entry>__u32</entry>
 261             <entry><structfield>count</structfield></entry>
 262             <entry>The number of controls in the controls array. May
 263 also be zero.</entry>
 264           </row>
 265           <row>
 266             <entry>__u32</entry>
 267             <entry><structfield>error_idx</structfield></entry>
 268             <entry><para>Set by the driver in case of an error. If the error is
 269 associated with a particular control, then <structfield>error_idx</structfield>
 270 is set to the index of that control. If the error is not related to a specific
 271 control, or the validation step failed (see below), then
 272 <structfield>error_idx</structfield> is set to <structfield>count</structfield>.
 273 The value is undefined if the ioctl returned 0 (success).</para>
 274
 275 <para>Before controls are read from/written to hardware a validation step
 276 takes place: this checks if all controls in the list are valid controls,
 277 if no attempt is made to write to a read-only control or read from a write-only
 278 control, and any other up-front checks that can be done without accessing the
 279 hardware. The exact validations done during this step are driver dependent
 280 since some checks might require hardware access for some devices, thus making
 281 it impossible to do those checks up-front. However, drivers should make a
 282 best-effort to do as many up-front checks as possible.</para>
 283
 284 <para>This check is done to avoid leaving the hardware in an inconsistent state due
 285 to easy-to-avoid problems. But it leads to another problem: the application needs to
 286 know whether an error came from the validation step (meaning that the hardware
 287 was not touched) or from an error during the actual reading from/writing to hardware.</para>
 288
 289 <para>The, in hindsight quite poor, solution for that is to set <structfield>error_idx</structfield>
 290 to <structfield>count</structfield> if the validation failed. This has the
 291 unfortunate side-effect that it is not possible to see which control failed the
 292 validation. If the validation was successful and the error happened while
 293 accessing the hardware, then <structfield>error_idx</structfield> is less than
 294 <structfield>count</structfield> and only the controls up to
 295 <structfield>error_idx-1</structfield> were read or written correctly, and the
 296 state of the remaining controls is undefined.</para>
 297
 298 <para>Since <constant>VIDIOC_TRY_EXT_CTRLS</constant> does not access hardware
 299 there is also no need to handle the validation step in this special way,
 300 so <structfield>error_idx</structfield> will just be set to the control that
 301 failed the validation step instead of to <structfield>count</structfield>.
 302 This means that if <constant>VIDIOC_S_EXT_CTRLS</constant> fails with
 303 <structfield>error_idx</structfield> set to <structfield>count</structfield>,
 304 then you can call <constant>VIDIOC_TRY_EXT_CTRLS</constant> to try to discover
 305 the actual control that failed the validation step. Unfortunately, there
 306 is no <constant>TRY</constant> equivalent for <constant>VIDIOC_G_EXT_CTRLS</constant>.
 307 </para></entry>
 308           </row>
 309           <row>
 310             <entry>__u32</entry>
 311             <entry><structfield>reserved</structfield>[2]</entry>
 312             <entry>Reserved for future extensions. Drivers and
 313 applications must set the array to zero.</entry>
 314           </row>
 315           <row>
 316             <entry>&v4l2-ext-control; *</entry>
 317             <entry><structfield>controls</structfield></entry>
 318             <entry>Pointer to an array of
 319 <structfield>count</structfield> v4l2_ext_control structures. Ignored
 320 if <structfield>count</structfield> equals zero.</entry>
 321           </row>
 322         </tbody>
 323       </tgroup>
 324     </table>
 325
 326     <table pgwide="1" frame="none" id="ctrl-class">
 327       <title>Control classes</title>
 328       <tgroup cols="3">
 329         &cs-def;
 330         <tbody valign="top">
 331           <row>
 332             <entry><constant>V4L2_CTRL_CLASS_USER</constant></entry>
 333             <entry>0x980000</entry>
 334             <entry>The class containing user controls. These controls
 335 are described in <xref linkend="control" />. All controls that can be set
 336 using the &VIDIOC-S-CTRL; and &VIDIOC-G-CTRL; ioctl belong to this
 337 class.</entry>
 338           </row>
 339           <row>
 340             <entry><constant>V4L2_CTRL_CLASS_MPEG</constant></entry>
 341             <entry>0x990000</entry>
 342             <entry>The class containing MPEG compression controls.
 343 These controls are described in <xref
 344                 linkend="mpeg-controls" />.</entry>
 345           </row>
 346           <row>
 347             <entry><constant>V4L2_CTRL_CLASS_CAMERA</constant></entry>
 348             <entry>0x9a0000</entry>
 349             <entry>The class containing camera controls.
 350 These controls are described in <xref
 351                 linkend="camera-controls" />.</entry>
 352           </row>
 353           <row>
 354             <entry><constant>V4L2_CTRL_CLASS_FM_TX</constant></entry>
 355             <entry>0x9b0000</entry>
 356             <entry>The class containing FM Transmitter (FM TX) controls.
 357 These controls are described in <xref
 358                 linkend="fm-tx-controls" />.</entry>
 359           </row>
 360           <row>
 361             <entry><constant>V4L2_CTRL_CLASS_FLASH</constant></entry>
 362             <entry>0x9c0000</entry>
 363             <entry>The class containing flash device controls.
 364 These controls are described in <xref
 365                 linkend="flash-controls" />.</entry>
 366           </row>
 367           <row>
 368             <entry><constant>V4L2_CTRL_CLASS_JPEG</constant></entry>
 369             <entry>0x9d0000</entry>
 370             <entry>The class containing JPEG compression controls.
 371 These controls are described in <xref
 372                 linkend="jpeg-controls" />.</entry>
 373           </row>
 374           <row>
 375             <entry><constant>V4L2_CTRL_CLASS_IMAGE_SOURCE</constant></entry>
 376             <entry>0x9e0000</entry> <entry>The class containing image
 377             source controls. These controls are described in <xref
 378             linkend="image-source-controls" />.</entry>
 379           </row>
 380           <row>
 381             <entry><constant>V4L2_CTRL_CLASS_IMAGE_PROC</constant></entry>
 382             <entry>0x9f0000</entry> <entry>The class containing image
 383             processing controls. These controls are described in <xref
 384             linkend="image-process-controls" />.</entry>
 385           </row>
 386
 387           <row>
 388             <entry><constant>V4L2_CTRL_CLASS_FM_RX</constant></entry>
 389             <entry>0xa10000</entry>
 390             <entry>The class containing FM Receiver (FM RX) controls.
 391 These controls are described in <xref
 392                 linkend="fm-rx-controls" />.</entry>
 393           </row>
 394           <row>
 395             <entry><constant>V4L2_CTRL_CLASS_RF_TUNER</constant></entry>
 396             <entry>0xa20000</entry>
 397             <entry>The class containing RF tuner controls.
 398 These controls are described in <xref linkend="rf-tuner-controls" />.</entry>
 399           </row>
 400         </tbody>
 401       </tgroup>
 402     </table>
 403
 404   </refsect1>
 405
 406   <refsect1>
 407     &return-value;
 408
 409     <variablelist>
 410       <varlistentry>
 411         <term><errorcode>EINVAL</errorcode></term>
 412         <listitem>
 413           <para>The &v4l2-ext-control; <structfield>id</structfield>
 414 is invalid, the &v4l2-ext-controls;
 415 <structfield>which</structfield> is invalid, or the &v4l2-ext-control;
 416 <structfield>value</structfield> was inappropriate (e.g. the given menu
 417 index is not supported by the driver). This error code is
 418 also returned by the <constant>VIDIOC_S_EXT_CTRLS</constant> and
 419 <constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctls if two or more
 420 control values are in conflict.</para>
 421         </listitem>
 422       </varlistentry>
 423       <varlistentry>
 424         <term><errorcode>ERANGE</errorcode></term>
 425         <listitem>
 426           <para>The &v4l2-ext-control; <structfield>value</structfield>
 427 is out of bounds.</para>
 428         </listitem>
 429       </varlistentry>
 430       <varlistentry>
 431         <term><errorcode>EBUSY</errorcode></term>
 432         <listitem>
 433           <para>The control is temporarily not changeable, possibly
 434 because another applications took over control of the device function
 435 this control belongs to.</para>
 436         </listitem>
 437       </varlistentry>
 438       <varlistentry>
 439         <term><errorcode>ENOSPC</errorcode></term>
 440         <listitem>
 441           <para>The space reserved for the control's payload is insufficient.
 442 The field <structfield>size</structfield> is set to a value that is enough
 443 to store the payload and this error code is returned.</para>
 444         </listitem>
 445       </varlistentry>
 446       <varlistentry>
 447         <term><errorcode>EACCES</errorcode></term>
 448         <listitem>
 449           <para>Attempt to try or set a read-only control or to get a
 450           write-only control.</para>
 451         </listitem>
 452       </varlistentry>
 453     </variablelist>
 454   </refsect1>
 455 </refentry>
 456