276 lines
9.0 KiB
XML
276 lines
9.0 KiB
XML
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<refentry id="vidioc-dbg-g-register">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_DBG_G_REGISTER</refname>
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<refname>VIDIOC_DBG_S_REGISTER</refname>
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<refpurpose>Read or write hardware registers</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_dbg_register *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>const struct v4l2_dbg_register
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*<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<note>
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<title>Experimental</title>
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<para>This is an <link linkend="experimental">experimental</link>
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interface and may change in the future.</para>
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</note>
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<para>For driver debugging purposes these ioctls allow test
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applications to access hardware registers directly. Regular
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applications must not use them.</para>
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<para>Since writing or even reading registers can jeopardize the
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system security, its stability and damage the hardware, both ioctls
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require superuser privileges. Additionally the Linux kernel must be
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compiled with the <constant>CONFIG_VIDEO_ADV_DEBUG</constant> option
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to enable these ioctls.</para>
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<para>To write a register applications must initialize all fields
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of a &v4l2-dbg-register; and call
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<constant>VIDIOC_DBG_S_REGISTER</constant> with a pointer to this
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structure. The <structfield>match.type</structfield> and
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<structfield>match.addr</structfield> or <structfield>match.name</structfield>
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fields select a chip on the TV
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card, the <structfield>reg</structfield> field specifies a register
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number and the <structfield>val</structfield> field the value to be
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written into the register.</para>
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<para>To read a register applications must initialize the
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<structfield>match.type</structfield>,
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<structfield>match.chip</structfield> or <structfield>match.name</structfield> and
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<structfield>reg</structfield> fields, and call
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<constant>VIDIOC_DBG_G_REGISTER</constant> with a pointer to this
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structure. On success the driver stores the register value in the
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<structfield>val</structfield> field. On failure the structure remains
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unchanged.</para>
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<para>When <structfield>match.type</structfield> is
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<constant>V4L2_CHIP_MATCH_HOST</constant>,
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<structfield>match.addr</structfield> selects the nth non-&i2c; chip
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on the TV card. The number zero always selects the host chip, ⪚ the
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chip connected to the PCI or USB bus. You can find out which chips are
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present with the &VIDIOC-DBG-G-CHIP-IDENT; ioctl.</para>
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<para>When <structfield>match.type</structfield> is
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<constant>V4L2_CHIP_MATCH_I2C_DRIVER</constant>,
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<structfield>match.name</structfield> contains the I2C driver name.
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For instance
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<constant>"saa7127"</constant> will match any chip
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supported by the saa7127 driver, regardless of its &i2c; bus address.
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When multiple chips supported by the same driver are present, the
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effect of these ioctls is undefined. Again with the
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&VIDIOC-DBG-G-CHIP-IDENT; ioctl you can find out which &i2c; chips are
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present.</para>
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<para>When <structfield>match.type</structfield> is
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<constant>V4L2_CHIP_MATCH_I2C_ADDR</constant>,
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<structfield>match.addr</structfield> selects a chip by its 7 bit &i2c;
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bus address.</para>
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<para>When <structfield>match.type</structfield> is
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<constant>V4L2_CHIP_MATCH_AC97</constant>,
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<structfield>match.addr</structfield> selects the nth AC97 chip
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on the TV card.</para>
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<note>
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<title>Success not guaranteed</title>
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<para>Due to a flaw in the Linux &i2c; bus driver these ioctls may
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return successfully without actually reading or writing a register. To
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catch the most likely failure we recommend a &VIDIOC-DBG-G-CHIP-IDENT;
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call confirming the presence of the selected &i2c; chip.</para>
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</note>
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<para>These ioctls are optional, not all drivers may support them.
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However when a driver supports these ioctls it must also support
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&VIDIOC-DBG-G-CHIP-IDENT;. Conversely it may support
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<constant>VIDIOC_DBG_G_CHIP_IDENT</constant> but not these ioctls.</para>
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<para><constant>VIDIOC_DBG_G_REGISTER</constant> and
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<constant>VIDIOC_DBG_S_REGISTER</constant> were introduced in Linux
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2.6.21, but their API was changed to the one described here in kernel 2.6.29.</para>
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<para>We recommended the <application>v4l2-dbg</application>
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utility over calling these ioctls directly. It is available from the
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LinuxTV v4l-dvb repository; see <ulink
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url="http://linuxtv.org/repo/">http://linuxtv.org/repo/</ulink> for
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access instructions.</para>
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<!-- Note for convenience vidioc-dbg-g-chip-ident.sgml
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contains a duplicate of this table. -->
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<table pgwide="1" frame="none" id="v4l2-dbg-match">
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<title>struct <structname>v4l2_dbg_match</structname></title>
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<tgroup cols="4">
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&cs-ustr;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>type</structfield></entry>
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<entry>See <xref linkend="ident-chip-match-types" /> for a list of
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possible types.</entry>
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</row>
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<row>
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<entry>union</entry>
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<entry>(anonymous)</entry>
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</row>
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<row>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>addr</structfield></entry>
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<entry>Match a chip by this number, interpreted according
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to the <structfield>type</structfield> field.</entry>
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</row>
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<row>
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<entry></entry>
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<entry>char</entry>
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<entry><structfield>name[32]</structfield></entry>
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<entry>Match a chip by this name, interpreted according
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to the <structfield>type</structfield> field.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-dbg-register">
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<title>struct <structname>v4l2_dbg_register</structname></title>
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<tgroup cols="4">
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<colspec colname="c1" />
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<colspec colname="c2" />
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<colspec colname="c4" />
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<tbody valign="top">
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<row>
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<entry>struct v4l2_dbg_match</entry>
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<entry><structfield>match</structfield></entry>
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<entry>How to match the chip, see <xref linkend="v4l2-dbg-match" />.</entry>
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</row>
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<row>
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<entry>__u64</entry>
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<entry><structfield>reg</structfield></entry>
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<entry>A register number.</entry>
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</row>
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<row>
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<entry>__u64</entry>
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<entry><structfield>val</structfield></entry>
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<entry>The value read from, or to be written into the
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register.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<!-- Note for convenience vidioc-dbg-g-chip-ident.sgml
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contains a duplicate of this table. -->
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<table pgwide="1" frame="none" id="chip-match-types">
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<title>Chip Match Types</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_CHIP_MATCH_HOST</constant></entry>
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<entry>0</entry>
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<entry>Match the nth chip on the card, zero for the
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host chip. Does not match &i2c; chips.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CHIP_MATCH_I2C_DRIVER</constant></entry>
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<entry>1</entry>
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<entry>Match an &i2c; chip by its driver name.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CHIP_MATCH_I2C_ADDR</constant></entry>
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<entry>2</entry>
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<entry>Match a chip by its 7 bit &i2c; bus address.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CHIP_MATCH_AC97</constant></entry>
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<entry>3</entry>
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<entry>Match the nth anciliary AC97 chip.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The driver does not support this ioctl, or the kernel
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was not compiled with the <constant>CONFIG_VIDEO_ADV_DEBUG</constant>
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option, or the <structfield>match_type</structfield> is invalid, or the
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selected chip or register does not exist.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EPERM</errorcode></term>
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<listitem>
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<para>Insufficient permissions. Root privileges are required
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to execute these ioctls.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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