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Diffstat (limited to 'kernel/Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml')
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diff --git a/kernel/Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml b/kernel/Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml new file mode 100644 index 000000000..c5bdbfcc4 --- /dev/null +++ b/kernel/Documentation/DocBook/media/v4l/vidioc-g-ext-ctrls.xml @@ -0,0 +1,427 @@ +<refentry id="vidioc-g-ext-ctrls"> + <refmeta> + <refentrytitle>ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, +VIDIOC_TRY_EXT_CTRLS</refentrytitle> + &manvol; + </refmeta> + + <refnamediv> + <refname>VIDIOC_G_EXT_CTRLS</refname> + <refname>VIDIOC_S_EXT_CTRLS</refname> + <refname>VIDIOC_TRY_EXT_CTRLS</refname> + <refpurpose>Get or set the value of several controls, try control +values</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_ext_controls +*<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_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, +VIDIOC_TRY_EXT_CTRLS</para> + </listitem> + </varlistentry> + <varlistentry> + <term><parameter>argp</parameter></term> + <listitem> + <para></para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Description</title> + + <para>These ioctls allow the caller to get or set multiple +controls atomically. Control IDs are grouped into control classes (see +<xref linkend="ctrl-class" />) and all controls in the control array +must belong to the same control class.</para> + + <para>Applications must always fill in the +<structfield>count</structfield>, +<structfield>ctrl_class</structfield>, +<structfield>controls</structfield> and +<structfield>reserved</structfield> fields of &v4l2-ext-controls;, and +initialize the &v4l2-ext-control; array pointed to by the +<structfield>controls</structfield> fields.</para> + + <para>To get the current value of a set of controls applications +initialize the <structfield>id</structfield>, +<structfield>size</structfield> and <structfield>reserved2</structfield> fields +of each &v4l2-ext-control; and call the +<constant>VIDIOC_G_EXT_CTRLS</constant> ioctl. String controls controls +must also set the <structfield>string</structfield> field. Controls +of compound types (<constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant> is set) +must set the <structfield>ptr</structfield> field.</para> + + <para>If the <structfield>size</structfield> is too small to +receive the control result (only relevant for pointer-type controls +like strings), then the driver will set <structfield>size</structfield> +to a valid value and return an &ENOSPC;. You should re-allocate the +memory to this new size and try again. For the string type it is possible that +the same issue occurs again if the string has grown in the meantime. It is +recommended to call &VIDIOC-QUERYCTRL; first and use +<structfield>maximum</structfield>+1 as the new <structfield>size</structfield> +value. It is guaranteed that that is sufficient memory. +</para> + + <para>N-dimensional arrays are set and retrieved row-by-row. You cannot set a partial +array, all elements have to be set or retrieved. The total size is calculated +as <structfield>elems</structfield> * <structfield>elem_size</structfield>. +These values can be obtained by calling &VIDIOC-QUERY-EXT-CTRL;.</para> + + <para>To change the value of a set of controls applications +initialize the <structfield>id</structfield>, <structfield>size</structfield>, +<structfield>reserved2</structfield> and +<structfield>value/value64/string/ptr</structfield> fields of each &v4l2-ext-control; and +call the <constant>VIDIOC_S_EXT_CTRLS</constant> ioctl. The controls +will only be set if <emphasis>all</emphasis> control values are +valid.</para> + + <para>To check if a set of controls have correct values applications +initialize the <structfield>id</structfield>, <structfield>size</structfield>, +<structfield>reserved2</structfield> and +<structfield>value/value64/string/ptr</structfield> fields of each &v4l2-ext-control; and +call the <constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctl. It is up to +the driver whether wrong values are automatically adjusted to a valid +value or if an error is returned.</para> + + <para>When the <structfield>id</structfield> or +<structfield>ctrl_class</structfield> is invalid drivers return an +&EINVAL;. When the value is out of bounds drivers can choose to take +the closest valid value or return an &ERANGE;, whatever seems more +appropriate. In the first case the new value is set in +&v4l2-ext-control;. If the new control value is inappropriate (e.g. the +given menu index is not supported by the menu control), then this will +also result in an &EINVAL; error.</para> + + <para>The driver will only set/get these controls if all control +values are correct. This prevents the situation where only some of the +controls were set/get. Only low-level errors (⪚ a failed i2c +command) can still cause this situation.</para> + + <table pgwide="1" frame="none" id="v4l2-ext-control"> + <title>struct <structname>v4l2_ext_control</structname></title> + <tgroup cols="4"> + &cs-ustr; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>id</structfield></entry> + <entry></entry> + <entry>Identifies the control, set by the +application.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>size</structfield></entry> + <entry></entry> + <entry>The total size in bytes of the payload of this +control. This is normally 0, but for pointer controls this should be +set to the size of the memory containing the payload, or that will +receive the payload. If <constant>VIDIOC_G_EXT_CTRLS</constant> finds +that this value is less than is required to store +the payload result, then it is set to a value large enough to store the +payload result and ENOSPC is returned. Note that for string controls +this <structfield>size</structfield> field should not be confused with the length of the string. +This field refers to the size of the memory that contains the string. +The actual <emphasis>length</emphasis> of the string may well be much smaller. +</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>reserved2</structfield>[1]</entry> + <entry></entry> + <entry>Reserved for future extensions. Drivers and +applications must set the array to zero.</entry> + </row> + <row> + <entry>union</entry> + <entry>(anonymous)</entry> + </row> + <row> + <entry></entry> + <entry>__s32</entry> + <entry><structfield>value</structfield></entry> + <entry>New value or current value. Valid if this control is not of +type <constant>V4L2_CTRL_TYPE_INTEGER64</constant> and +<constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant> is not set.</entry> + </row> + <row> + <entry></entry> + <entry>__s64</entry> + <entry><structfield>value64</structfield></entry> + <entry>New value or current value. Valid if this control is of +type <constant>V4L2_CTRL_TYPE_INTEGER64</constant> and +<constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant> is not set.</entry> + </row> + <row> + <entry></entry> + <entry>char *</entry> + <entry><structfield>string</structfield></entry> + <entry>A pointer to a string. Valid if this control is of +type <constant>V4L2_CTRL_TYPE_STRING</constant>.</entry> + </row> + <row> + <entry></entry> + <entry>__u8 *</entry> + <entry><structfield>p_u8</structfield></entry> + <entry>A pointer to a matrix control of unsigned 8-bit values. +Valid if this control is of type <constant>V4L2_CTRL_TYPE_U8</constant>.</entry> + </row> + <row> + <entry></entry> + <entry>__u16 *</entry> + <entry><structfield>p_u16</structfield></entry> + <entry>A pointer to a matrix control of unsigned 16-bit values. +Valid if this control is of type <constant>V4L2_CTRL_TYPE_U16</constant>.</entry> + </row> + <row> + <entry></entry> + <entry>void *</entry> + <entry><structfield>ptr</structfield></entry> + <entry>A pointer to a compound type which can be an N-dimensional array and/or a +compound type (the control's type is >= <constant>V4L2_CTRL_COMPOUND_TYPES</constant>). +Valid if <constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant> is set for this control. +</entry> + </row> + </tbody> + </tgroup> + </table> + + <table pgwide="1" frame="none" id="v4l2-ext-controls"> + <title>struct <structname>v4l2_ext_controls</structname></title> + <tgroup cols="3"> + &cs-str; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>ctrl_class</structfield></entry> + <entry>The control class to which all controls belong, see +<xref linkend="ctrl-class" />. Drivers that use a kernel framework for handling +controls will also accept a value of 0 here, meaning that the controls can +belong to any control class. Whether drivers support this can be tested by setting +<structfield>ctrl_class</structfield> to 0 and calling <constant>VIDIOC_TRY_EXT_CTRLS</constant> +with a <structfield>count</structfield> of 0. If that succeeds, then the driver +supports this feature.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>count</structfield></entry> + <entry>The number of controls in the controls array. May +also be zero.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>error_idx</structfield></entry> + <entry><para>Set by the driver in case of an error. If the error is +associated with a particular control, then <structfield>error_idx</structfield> +is set to the index of that control. If the error is not related to a specific +control, or the validation step failed (see below), then +<structfield>error_idx</structfield> is set to <structfield>count</structfield>. +The value is undefined if the ioctl returned 0 (success).</para> + +<para>Before controls are read from/written to hardware a validation step +takes place: this checks if all controls in the list are valid controls, +if no attempt is made to write to a read-only control or read from a write-only +control, and any other up-front checks that can be done without accessing the +hardware. The exact validations done during this step are driver dependent +since some checks might require hardware access for some devices, thus making +it impossible to do those checks up-front. However, drivers should make a +best-effort to do as many up-front checks as possible.</para> + +<para>This check is done to avoid leaving the hardware in an inconsistent state due +to easy-to-avoid problems. But it leads to another problem: the application needs to +know whether an error came from the validation step (meaning that the hardware +was not touched) or from an error during the actual reading from/writing to hardware.</para> + +<para>The, in hindsight quite poor, solution for that is to set <structfield>error_idx</structfield> +to <structfield>count</structfield> if the validation failed. This has the +unfortunate side-effect that it is not possible to see which control failed the +validation. If the validation was successful and the error happened while +accessing the hardware, then <structfield>error_idx</structfield> is less than +<structfield>count</structfield> and only the controls up to +<structfield>error_idx-1</structfield> were read or written correctly, and the +state of the remaining controls is undefined.</para> + +<para>Since <constant>VIDIOC_TRY_EXT_CTRLS</constant> does not access hardware +there is also no need to handle the validation step in this special way, +so <structfield>error_idx</structfield> will just be set to the control that +failed the validation step instead of to <structfield>count</structfield>. +This means that if <constant>VIDIOC_S_EXT_CTRLS</constant> fails with +<structfield>error_idx</structfield> set to <structfield>count</structfield>, +then you can call <constant>VIDIOC_TRY_EXT_CTRLS</constant> to try to discover +the actual control that failed the validation step. Unfortunately, there +is no <constant>TRY</constant> equivalent for <constant>VIDIOC_G_EXT_CTRLS</constant>. +</para></entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>reserved</structfield>[2]</entry> + <entry>Reserved for future extensions. Drivers and +applications must set the array to zero.</entry> + </row> + <row> + <entry>&v4l2-ext-control; *</entry> + <entry><structfield>controls</structfield></entry> + <entry>Pointer to an array of +<structfield>count</structfield> v4l2_ext_control structures. Ignored +if <structfield>count</structfield> equals zero.</entry> + </row> + </tbody> + </tgroup> + </table> + + <table pgwide="1" frame="none" id="ctrl-class"> + <title>Control classes</title> + <tgroup cols="3"> + &cs-def; + <tbody valign="top"> + <row> + <entry><constant>V4L2_CTRL_CLASS_USER</constant></entry> + <entry>0x980000</entry> + <entry>The class containing user controls. These controls +are described in <xref linkend="control" />. All controls that can be set +using the &VIDIOC-S-CTRL; and &VIDIOC-G-CTRL; ioctl belong to this +class.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_CLASS_MPEG</constant></entry> + <entry>0x990000</entry> + <entry>The class containing MPEG compression controls. +These controls are described in <xref + linkend="mpeg-controls" />.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_CLASS_CAMERA</constant></entry> + <entry>0x9a0000</entry> + <entry>The class containing camera controls. +These controls are described in <xref + linkend="camera-controls" />.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_CLASS_FM_TX</constant></entry> + <entry>0x9b0000</entry> + <entry>The class containing FM Transmitter (FM TX) controls. +These controls are described in <xref + linkend="fm-tx-controls" />.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_CLASS_FLASH</constant></entry> + <entry>0x9c0000</entry> + <entry>The class containing flash device controls. +These controls are described in <xref + linkend="flash-controls" />.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_CLASS_JPEG</constant></entry> + <entry>0x9d0000</entry> + <entry>The class containing JPEG compression controls. +These controls are described in <xref + linkend="jpeg-controls" />.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_CLASS_IMAGE_SOURCE</constant></entry> + <entry>0x9e0000</entry> <entry>The class containing image + source controls. These controls are described in <xref + linkend="image-source-controls" />.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_CLASS_IMAGE_PROC</constant></entry> + <entry>0x9f0000</entry> <entry>The class containing image + processing controls. These controls are described in <xref + linkend="image-process-controls" />.</entry> + </row> + + <row> + <entry><constant>V4L2_CTRL_CLASS_FM_RX</constant></entry> + <entry>0xa10000</entry> + <entry>The class containing FM Receiver (FM RX) controls. +These controls are described in <xref + linkend="fm-rx-controls" />.</entry> + </row> + <row> + <entry><constant>V4L2_CTRL_CLASS_RF_TUNER</constant></entry> + <entry>0xa20000</entry> + <entry>The class containing RF tuner controls. +These controls are described in <xref linkend="rf-tuner-controls" />.</entry> + </row> + </tbody> + </tgroup> + </table> + + </refsect1> + + <refsect1> + &return-value; + + <variablelist> + <varlistentry> + <term><errorcode>EINVAL</errorcode></term> + <listitem> + <para>The &v4l2-ext-control; <structfield>id</structfield> +is invalid, the &v4l2-ext-controls; +<structfield>ctrl_class</structfield> is invalid, or the &v4l2-ext-control; +<structfield>value</structfield> was inappropriate (e.g. the given menu +index is not supported by the driver). This error code is +also returned by the <constant>VIDIOC_S_EXT_CTRLS</constant> and +<constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctls if two or more +control values are in conflict.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><errorcode>ERANGE</errorcode></term> + <listitem> + <para>The &v4l2-ext-control; <structfield>value</structfield> +is out of bounds.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><errorcode>EBUSY</errorcode></term> + <listitem> + <para>The control is temporarily not changeable, possibly +because another applications took over control of the device function +this control belongs to.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><errorcode>ENOSPC</errorcode></term> + <listitem> + <para>The space reserved for the control's payload is insufficient. +The field <structfield>size</structfield> is set to a value that is enough +to store the payload and this error code is returned.</para> + </listitem> + </varlistentry> + <varlistentry> + <term><errorcode>EACCES</errorcode></term> + <listitem> + <para>Attempt to try or set a read-only control or to get a + write-only control.</para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> +</refentry> + |