diff options
author | 2015-08-04 12:17:53 -0700 | |
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committer | 2015-08-04 15:44:42 -0700 | |
commit | 9ca8dbcc65cfc63d6f5ef3312a33184e1d726e00 (patch) | |
tree | 1c9cafbcd35f783a87880a10f85d1a060db1a563 /kernel/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml | |
parent | 98260f3884f4a202f9ca5eabed40b1354c489b29 (diff) |
Add the rt linux 4.1.3-rt3 as base
Import the rt linux 4.1.3-rt3 as OPNFV kvm base.
It's from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-4.1.y-rt and
the base is:
commit 0917f823c59692d751951bf5ea699a2d1e2f26a2
Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Sat Jul 25 12:13:34 2015 +0200
Prepare v4.1.3-rt3
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
We lose all the git history this way and it's not good. We
should apply another opnfv project repo in future.
Change-Id: I87543d81c9df70d99c5001fbdf646b202c19f423
Signed-off-by: Yunhong Jiang <yunhong.jiang@intel.com>
Diffstat (limited to 'kernel/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml')
-rw-r--r-- | kernel/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml | 650 |
1 files changed, 650 insertions, 0 deletions
diff --git a/kernel/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml b/kernel/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml new file mode 100644 index 000000000..dc83ad70f --- /dev/null +++ b/kernel/Documentation/DocBook/media/v4l/vidioc-queryctrl.xml @@ -0,0 +1,650 @@ +<refentry id="vidioc-queryctrl"> + <refmeta> + <refentrytitle>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU</refentrytitle> + &manvol; + </refmeta> + + <refnamediv> + <refname>VIDIOC_QUERYCTRL</refname> + <refname>VIDIOC_QUERY_EXT_CTRL</refname> + <refname>VIDIOC_QUERYMENU</refname> + <refpurpose>Enumerate controls and menu control items</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <funcsynopsis> + <funcprototype> + <funcdef>int <function>ioctl</function></funcdef> + <paramdef>int <parameter>fd</parameter></paramdef> + <paramdef>int <parameter>request</parameter></paramdef> + <paramdef>struct v4l2_queryctrl *<parameter>argp</parameter></paramdef> + </funcprototype> + </funcsynopsis> + <funcsynopsis> + <funcprototype> + <funcdef>int <function>ioctl</function></funcdef> + <paramdef>int <parameter>fd</parameter></paramdef> + <paramdef>int <parameter>request</parameter></paramdef> + <paramdef>struct v4l2_query_ext_ctrl *<parameter>argp</parameter></paramdef> + </funcprototype> + </funcsynopsis> + <funcsynopsis> + <funcprototype> + <funcdef>int <function>ioctl</function></funcdef> + <paramdef>int <parameter>fd</parameter></paramdef> + <paramdef>int <parameter>request</parameter></paramdef> + <paramdef>struct v4l2_querymenu *<parameter>argp</parameter></paramdef> + </funcprototype> + </funcsynopsis> + </refsynopsisdiv> + + <refsect1> + <title>Arguments</title> + + <variablelist> + <varlistentry> + <term><parameter>fd</parameter></term> + <listitem> + <para>&fd;</para> + </listitem> + </varlistentry> + <varlistentry> + <term><parameter>request</parameter></term> + <listitem> + <para>VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU</para> + </listitem> + </varlistentry> + <varlistentry> + <term><parameter>argp</parameter></term> + <listitem> + <para></para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Description</title> + + <para>To query the attributes of a control applications set the +<structfield>id</structfield> field of a &v4l2-queryctrl; and call the +<constant>VIDIOC_QUERYCTRL</constant> ioctl with a pointer to this +structure. The driver fills the rest of the structure or returns an +&EINVAL; when the <structfield>id</structfield> is invalid.</para> + + <para>It is possible to enumerate controls by calling +<constant>VIDIOC_QUERYCTRL</constant> with successive +<structfield>id</structfield> values starting from +<constant>V4L2_CID_BASE</constant> up to and exclusive +<constant>V4L2_CID_LASTP1</constant>. Drivers may return +<errorcode>EINVAL</errorcode> if a control in this range is not +supported. Further applications can enumerate private controls, which +are not defined in this specification, by starting at +<constant>V4L2_CID_PRIVATE_BASE</constant> and incrementing +<structfield>id</structfield> until the driver returns +<errorcode>EINVAL</errorcode>.</para> + + <para>In both cases, when the driver sets the +<constant>V4L2_CTRL_FLAG_DISABLED</constant> flag in the +<structfield>flags</structfield> field this control is permanently +disabled and should be ignored by the application.<footnote> + <para><constant>V4L2_CTRL_FLAG_DISABLED</constant> was +intended for two purposes: Drivers can skip predefined controls not +supported by the hardware (although returning EINVAL would do as +well), or disable predefined and private controls after hardware +detection without the trouble of reordering control arrays and indices +(EINVAL cannot be used to skip private controls because it would +prematurely end the enumeration).</para></footnote></para> + + <para>When the application ORs <structfield>id</structfield> with +<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver returns the +next supported non-compound control, or <errorcode>EINVAL</errorcode> +if there is none. In addition, the <constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant> +flag can be specified to enumerate all compound controls (i.e. controls +with type ≥ <constant>V4L2_CTRL_COMPOUND_TYPES</constant>). Specify both +<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> and +<constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant> in order to enumerate +all controls, compound or not. Drivers which do not support these flags yet +always return <errorcode>EINVAL</errorcode>.</para> + + <para>The <constant>VIDIOC_QUERY_EXT_CTRL</constant> ioctl was +introduced in order to better support controls that can use compound +types, and to expose additional control information that cannot be +returned in &v4l2-queryctrl; since that structure is full.</para> + + <para><constant>VIDIOC_QUERY_EXT_CTRL</constant> is used in the +same way as <constant>VIDIOC_QUERYCTRL</constant>, except that the +<structfield>reserved</structfield> array must be zeroed as well.</para> + + <para>Additional information is required for menu controls: the +names of the menu items. To query them applications set the +<structfield>id</structfield> and <structfield>index</structfield> +fields of &v4l2-querymenu; and call the +<constant>VIDIOC_QUERYMENU</constant> ioctl with a pointer to this +structure. The driver fills the rest of the structure or returns an +&EINVAL; when the <structfield>id</structfield> or +<structfield>index</structfield> is invalid. Menu items are enumerated +by calling <constant>VIDIOC_QUERYMENU</constant> with successive +<structfield>index</structfield> values from &v4l2-queryctrl; +<structfield>minimum</structfield> to +<structfield>maximum</structfield>, inclusive. Note that it is possible +for <constant>VIDIOC_QUERYMENU</constant> to return an &EINVAL; for some +indices between <structfield>minimum</structfield> and <structfield>maximum</structfield>. +In that case that particular menu item is not supported by this driver. Also note that +the <structfield>minimum</structfield> value is not necessarily 0.</para> + + <para>See also the examples in <xref linkend="control" />.</para> + + <table pgwide="1" frame="none" id="v4l2-queryctrl"> + <title>struct <structname>v4l2_queryctrl</structname></title> + <tgroup cols="3"> + &cs-str; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>id</structfield></entry> + <entry>Identifies the control, set by the application. See +<xref linkend="control-id" /> for predefined IDs. When the ID is ORed +with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns +the first control with a higher ID. Drivers which do not support this +flag yet always return an &EINVAL;.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>type</structfield></entry> + <entry>Type of control, see <xref + linkend="v4l2-ctrl-type" />.</entry> + </row> + <row> + <entry>__u8</entry> + <entry><structfield>name</structfield>[32]</entry> + <entry>Name of the control, a NUL-terminated ASCII +string. This information is intended for the user.</entry> + </row> + <row> + <entry>__s32</entry> + <entry><structfield>minimum</structfield></entry> + <entry>Minimum value, inclusive. This field gives a lower +bound for the control. See &v4l2-ctrl-type; how the minimum value is to +be used for each possible control type. Note that this a signed 32-bit value.</entry> + </row> + <row> + <entry>__s32</entry> + <entry><structfield>maximum</structfield></entry> + <entry>Maximum value, inclusive. This field gives an upper +bound for the control. See &v4l2-ctrl-type; how the maximum value is to +be used for each possible control type. Note that this a signed 32-bit value.</entry> + </row> + <row> + <entry>__s32</entry> + <entry><structfield>step</structfield></entry> + <entry><para>This field gives a step size for the control. +See &v4l2-ctrl-type; how the step value is to be used for each possible +control type. Note that this an unsigned 32-bit value. +</para><para>Generally drivers should not scale hardware +control values. It may be necessary for example when the +<structfield>name</structfield> or <structfield>id</structfield> imply +a particular unit and the hardware actually accepts only multiples of +said unit. If so, drivers must take care values are properly rounded +when scaling, such that errors will not accumulate on repeated +read-write cycles.</para><para>This field gives the smallest change of +an integer control actually affecting hardware. Often the information +is needed when the user can change controls by keyboard or GUI +buttons, rather than a slider. When for example a hardware register +accepts values 0-511 and the driver reports 0-65535, step should be +128.</para><para>Note that although signed, the step value is supposed to +be always positive.</para></entry> + </row> + <row> + <entry>__s32</entry> + <entry><structfield>default_value</structfield></entry> + <entry>The default value of a +<constant>V4L2_CTRL_TYPE_INTEGER</constant>, +<constant>_BOOLEAN</constant>, <constant>_BITMASK</constant>, +<constant>_MENU</constant> or <constant>_INTEGER_MENU</constant> control. +Not valid for other types of controls. +Note that drivers reset controls to their default value only when the +driver is first loaded, never afterwards.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>flags</structfield></entry> + <entry>Control flags, see <xref + linkend="control-flags" />.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>reserved</structfield>[2]</entry> + <entry>Reserved for future extensions. Drivers must set +the array to zero.</entry> + </row> + </tbody> + </tgroup> + </table> + + <table pgwide="1" frame="none" id="v4l2-query-ext-ctrl"> + <title>struct <structname>v4l2_query_ext_ctrl</structname></title> + <tgroup cols="3"> + &cs-str; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>id</structfield></entry> + <entry>Identifies the control, set by the application. See +<xref linkend="control-id" /> for predefined IDs. When the ID is ORed +with <constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver clears the +flag and returns the first non-compound control with a higher ID. When the +ID is ORed with <constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant> the driver +clears the flag and returns the first compound control with a higher ID. +Set both to get the first control (compound or not) with a higher ID.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>type</structfield></entry> + <entry>Type of control, see <xref + linkend="v4l2-ctrl-type" />.</entry> + </row> + <row> + <entry>char</entry> + <entry><structfield>name</structfield>[32]</entry> + <entry>Name of the control, a NUL-terminated ASCII +string. This information is intended for the user.</entry> + </row> + <row> + <entry>__s64</entry> + <entry><structfield>minimum</structfield></entry> + <entry>Minimum value, inclusive. This field gives a lower +bound for the control. See &v4l2-ctrl-type; how the minimum value is to +be used for each possible control type. Note that this a signed 64-bit value.</entry> + </row> + <row> + <entry>__s64</entry> + <entry><structfield>maximum</structfield></entry> + <entry>Maximum value, inclusive. This field gives an upper +bound for the control. See &v4l2-ctrl-type; how the maximum value is to +be used for each possible control type. Note that this a signed 64-bit value.</entry> + </row> + <row> + <entry>__u64</entry> + <entry><structfield>step</structfield></entry> + <entry><para>This field gives a step size for the control. +See &v4l2-ctrl-type; how the step value is to be used for each possible +control type. Note that this an unsigned 64-bit value. +</para><para>Generally drivers should not scale hardware +control values. It may be necessary for example when the +<structfield>name</structfield> or <structfield>id</structfield> imply +a particular unit and the hardware actually accepts only multiples of +said unit. If so, drivers must take care values are properly rounded +when scaling, such that errors will not accumulate on repeated +read-write cycles.</para><para>This field gives the smallest change of +an integer control actually affecting hardware. Often the information +is needed when the user can change controls by keyboard or GUI +buttons, rather than a slider. When for example a hardware register +accepts values 0-511 and the driver reports 0-65535, step should be +128.</para></entry> + </row> + <row> + <entry>__s64</entry> + <entry><structfield>default_value</structfield></entry> + <entry>The default value of a +<constant>V4L2_CTRL_TYPE_INTEGER</constant>, <constant>_INTEGER64</constant>, +<constant>_BOOLEAN</constant>, <constant>_BITMASK</constant>, +<constant>_MENU</constant>, <constant>_INTEGER_MENU</constant>, +<constant>_U8</constant> or <constant>_U16</constant> control. +Not valid for other types of controls. +Note that drivers reset controls to their default value only when the +driver is first loaded, never afterwards. +</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>flags</structfield></entry> + <entry>Control flags, see <xref + linkend="control-flags" />.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>elem_size</structfield></entry> + <entry>The size in bytes of a single element of the array. +Given a char pointer <constant>p</constant> to a 3-dimensional array you can find the +position of cell <constant>(z, y, x)</constant> as follows: +<constant>p + ((z * dims[1] + y) * dims[0] + x) * elem_size</constant>. <structfield>elem_size</structfield> +is always valid, also when the control isn't an array. For string controls +<structfield>elem_size</structfield> is equal to <structfield>maximum + 1</structfield>. +</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>elems</structfield></entry> + <entry>The number of elements in the N-dimensional array. If this control +is not an array, then <structfield>elems</structfield> is 1. The <structfield>elems</structfield> +field can never be 0.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>nr_of_dims</structfield></entry> + <entry>The number of dimension in the N-dimensional array. If this control +is not an array, then this field is 0.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>dims[V4L2_CTRL_MAX_DIMS]</structfield></entry> + <entry>The size of each dimension. The first <structfield>nr_of_dims</structfield> +elements of this array must be non-zero, all remaining elements must be zero.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>reserved</structfield>[32]</entry> + <entry>Reserved for future extensions. Applications and drivers +must set the array to zero.</entry> + </row> + </tbody> + </tgroup> + </table> + + <table pgwide="1" frame="none" id="v4l2-querymenu"> + <title>struct <structname>v4l2_querymenu</structname></title> + <tgroup cols="4"> + &cs-str; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry></entry> + <entry><structfield>id</structfield></entry> + <entry>Identifies the control, set by the application +from the respective &v4l2-queryctrl; +<structfield>id</structfield>.</entry> + </row> + <row> + <entry>__u32</entry> + <entry></entry> + <entry><structfield>index</structfield></entry> + <entry>Index of the menu item, starting at zero, set by + the application.</entry> + </row> + <row> + <entry>union</entry> + <entry></entry> + <entry></entry> + <entry></entry> + </row> + <row> + <entry></entry> + <entry>__u8</entry> + <entry><structfield>name</structfield>[32]</entry> + <entry>Name of the menu item, a NUL-terminated ASCII +string. This information is intended for the user. This field is valid +for <constant>V4L2_CTRL_FLAG_MENU</constant> type controls.</entry> + </row> + <row> + <entry></entry> + <entry>__s64</entry> + <entry><structfield>value</structfield></entry> + <entry> + Value of the integer menu item. This field is valid for + <constant>V4L2_CTRL_FLAG_INTEGER_MENU</constant> type + controls. + </entry> + </row> + <row> + <entry>__u32</entry> + <entry></entry> + <entry><structfield>reserved</structfield></entry> + <entry>Reserved for future extensions. Drivers must set +the array to zero.</entry> + </row> + </tbody> + </tgroup> + </table> + + <table pgwide="1" frame="none" id="v4l2-ctrl-type"> + <title>enum v4l2_ctrl_type</title> + <tgroup cols="5" align="left"> + <colspec colwidth="30*" /> + <colspec colwidth="5*" align="center" /> + <colspec colwidth="5*" align="center" /> + <colspec colwidth="5*" align="center" /> + <colspec colwidth="55*" /> + <thead> + <row> + <entry>Type</entry> + <entry><structfield>minimum</structfield></entry> + <entry><structfield>step</structfield></entry> + <entry><structfield>maximum</structfield></entry> + <entry>Description</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry><constant>V4L2_CTRL_TYPE_INTEGER</constant></entry> + <entry>any</entry> + <entry>any</entry> + <entry>any</entry> + <entry>An integer-valued control ranging from minimum to +maximum inclusive. The step value indicates the increment between +values which are actually different on the hardware.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_BOOLEAN</constant></entry> + <entry>0</entry> + <entry>1</entry> + <entry>1</entry> + <entry>A boolean-valued control. Zero corresponds to +"disabled", and one means "enabled".</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_MENU</constant></entry> + <entry>≥ 0</entry> + <entry>1</entry> + <entry>N-1</entry> + <entry>The control has a menu of N choices. The names of +the menu items can be enumerated with the +<constant>VIDIOC_QUERYMENU</constant> ioctl.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_INTEGER_MENU</constant></entry> + <entry>≥ 0</entry> + <entry>1</entry> + <entry>N-1</entry> + <entry> + The control has a menu of N choices. The values of the + menu items can be enumerated with the + <constant>VIDIOC_QUERYMENU</constant> ioctl. This is + similar to <constant>V4L2_CTRL_TYPE_MENU</constant> + except that instead of strings, the menu items are + signed 64-bit integers. + </entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_BITMASK</constant></entry> + <entry>0</entry> + <entry>n/a</entry> + <entry>any</entry> + <entry>A bitmask field. The maximum value is the set of bits that can +be used, all other bits are to be 0. The maximum value is interpreted as a __u32, +allowing the use of bit 31 in the bitmask.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_BUTTON</constant></entry> + <entry>0</entry> + <entry>0</entry> + <entry>0</entry> + <entry>A control which performs an action when set. +Drivers must ignore the value passed with +<constant>VIDIOC_S_CTRL</constant> and return an &EINVAL; on a +<constant>VIDIOC_G_CTRL</constant> attempt.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_INTEGER64</constant></entry> + <entry>any</entry> + <entry>any</entry> + <entry>any</entry> + <entry>A 64-bit integer valued control. Minimum, maximum +and step size cannot be queried using <constant>VIDIOC_QUERYCTRL</constant>. +Only <constant>VIDIOC_QUERY_EXT_CTRL</constant> can retrieve the 64-bit +min/max/step values, they should be interpreted as n/a when using +<constant>VIDIOC_QUERYCTRL</constant>.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_STRING</constant></entry> + <entry>≥ 0</entry> + <entry>≥ 1</entry> + <entry>≥ 0</entry> + <entry>The minimum and maximum string lengths. The step size +means that the string must be (minimum + N * step) characters long for +N ≥ 0. These lengths do not include the terminating zero, so in order to +pass a string of length 8 to &VIDIOC-S-EXT-CTRLS; you need to set the +<structfield>size</structfield> field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can +set the <structfield>size</structfield> field to <structfield>maximum</structfield> + 1. +Which character encoding is used will depend on the string control itself and +should be part of the control documentation.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry> + <entry>n/a</entry> + <entry>n/a</entry> + <entry>n/a</entry> + <entry>This is not a control. When +<constant>VIDIOC_QUERYCTRL</constant> is called with a control ID +equal to a control class code (see <xref linkend="ctrl-class" />) + 1, the +ioctl returns the name of the control class and this control type. +Older drivers which do not support this feature return an +&EINVAL;.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_U8</constant></entry> + <entry>any</entry> + <entry>any</entry> + <entry>any</entry> + <entry>An unsigned 8-bit valued control ranging from minimum to +maximum inclusive. The step value indicates the increment between +values which are actually different on the hardware. +</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_TYPE_U16</constant></entry> + <entry>any</entry> + <entry>any</entry> + <entry>any</entry> + <entry>An unsigned 16-bit valued control ranging from minimum to +maximum inclusive. The step value indicates the increment between +values which are actually different on the hardware. +</entry> + </row> + </tbody> + </tgroup> + </table> + + <table pgwide="1" frame="none" id="control-flags"> + <title>Control Flags</title> + <tgroup cols="3"> + &cs-def; + <tbody valign="top"> + <row> + <entry><constant>V4L2_CTRL_FLAG_DISABLED</constant></entry> + <entry>0x0001</entry> + <entry>This control is permanently disabled and should be +ignored by the application. Any attempt to change the control will +result in an &EINVAL;.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_FLAG_GRABBED</constant></entry> + <entry>0x0002</entry> + <entry>This control is temporarily unchangeable, for +example because another application took over control of the +respective resource. Such controls may be displayed specially in a +user interface. Attempts to change the control may result in an +&EBUSY;.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_FLAG_READ_ONLY</constant></entry> + <entry>0x0004</entry> + <entry>This control is permanently readable only. Any +attempt to change the control will result in an &EINVAL;.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_FLAG_UPDATE</constant></entry> + <entry>0x0008</entry> + <entry>A hint that changing this control may affect the +value of other controls within the same control class. Applications +should update their user interface accordingly.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_FLAG_INACTIVE</constant></entry> + <entry>0x0010</entry> + <entry>This control is not applicable to the current +configuration and should be displayed accordingly in a user interface. +For example the flag may be set on a MPEG audio level 2 bitrate +control when MPEG audio encoding level 1 was selected with another +control.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_FLAG_SLIDER</constant></entry> + <entry>0x0020</entry> + <entry>A hint that this control is best represented as a +slider-like element in a user interface.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant></entry> + <entry>0x0040</entry> + <entry>This control is permanently writable only. Any +attempt to read the control will result in an &EACCES; error code. This +flag is typically present for relative controls or action controls where +writing a value will cause the device to carry out a given action +(⪚ motor control) but no meaningful value can be returned.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_FLAG_VOLATILE</constant></entry> + <entry>0x0080</entry> + <entry>This control is volatile, which means that the value of the control +changes continuously. A typical example would be the current gain value if the device +is in auto-gain mode. In such a case the hardware calculates the gain value based on +the lighting conditions which can change over time. Note that setting a new value for +a volatile control will have no effect and no <constant>V4L2_EVENT_CTRL_CH_VALUE</constant> +will be sent, unless the <constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant> flag +(see below) is also set. Otherwise the new value will just be ignored.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant></entry> + <entry>0x0100</entry> + <entry>This control has a pointer type, so its value has to be accessed +using one of the pointer fields of &v4l2-ext-control;. This flag is set for controls +that are an array, string, or have a compound type. In all cases you have to set a +pointer to memory containing the payload of the control.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant></entry> + <entry>0x0200</entry> + <entry>The value provided to the control will be propagated to the driver +even if remains constant. This is required when the control represents an action +on the hardware. For example: clearing an error flag or triggering the flash. All the +controls of the type <constant>V4L2_CTRL_TYPE_BUTTON</constant> have this flag set.</entry> + </row> + </tbody> + </tgroup> + </table> + </refsect1> + + <refsect1> + &return-value; + + <variablelist> + <varlistentry> + <term><errorcode>EINVAL</errorcode></term> + <listitem> + <para>The &v4l2-queryctrl; <structfield>id</structfield> +is invalid. The &v4l2-querymenu; <structfield>id</structfield> is +invalid or <structfield>index</structfield> is out of range (less than +<structfield>minimum</structfield> or greater than <structfield>maximum</structfield>) +or this particular menu item is not supported by the driver.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><errorcode>EACCES</errorcode></term> + <listitem> + <para>An attempt was made to read a write-only control.</para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> +</refentry> |