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