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Diffstat (limited to 'Documentation/DocBook/media/v4l/vidioc-dbg-g-register.xml')
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diff --git a/Documentation/DocBook/media/v4l/vidioc-dbg-g-register.xml b/Documentation/DocBook/media/v4l/vidioc-dbg-g-register.xml new file mode 100644 index 0000000..a44aebc --- /dev/null +++ b/Documentation/DocBook/media/v4l/vidioc-dbg-g-register.xml @@ -0,0 +1,258 @@ +<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, ⪚ 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> |