About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

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

Custom Search

Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.

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>
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>
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>
28	  <refsect1>
29	    <title>Arguments</title>
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>
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>
54	  <refsect1>
55	    <title>Description</title>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
404	  </refsect1>
406	  <refsect1>
407	    &return-value;
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>
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.