Documentation/DocBook/media/v4l/vidioc-dbg-g-register.xml

   1 <refentry id="vidioc-dbg-g-register">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_DBG_G_REGISTER</refname>
   9     <refname>VIDIOC_DBG_S_REGISTER</refname>
  10     <refpurpose>Read or write hardware registers</refpurpose>
  11   </refnamediv>
  12
  13   <refsynopsisdiv>
  14     <funcsynopsis>
  15       <funcprototype>
  16         <funcdef>int <function>ioctl</function></funcdef>
  17         <paramdef>int <parameter>fd</parameter></paramdef>
  18         <paramdef>int <parameter>request</parameter></paramdef>
  19         <paramdef>struct v4l2_dbg_register *<parameter>argp</parameter></paramdef>
  20       </funcprototype>
  21     </funcsynopsis>
  22     <funcsynopsis>
  23       <funcprototype>
  24         <funcdef>int <function>ioctl</function></funcdef>
  25         <paramdef>int <parameter>fd</parameter></paramdef>
  26         <paramdef>int <parameter>request</parameter></paramdef>
  27         <paramdef>const struct v4l2_dbg_register
  28 *<parameter>argp</parameter></paramdef>
  29       </funcprototype>
  30     </funcsynopsis>
  31   </refsynopsisdiv>
  32
  33   <refsect1>
  34     <title>Arguments</title>
  35
  36     <variablelist>
  37       <varlistentry>
  38         <term><parameter>fd</parameter></term>
  39         <listitem>
  40           <para>&fd;</para>
  41         </listitem>
  42       </varlistentry>
  43       <varlistentry>
  44         <term><parameter>request</parameter></term>
  45         <listitem>
  46           <para>VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER</para>
  47         </listitem>
  48       </varlistentry>
  49       <varlistentry>
  50         <term><parameter>argp</parameter></term>
  51         <listitem>
  52           <para></para>
  53         </listitem>
  54       </varlistentry>
  55     </variablelist>
  56   </refsect1>
  57
  58   <refsect1>
  59     <title>Description</title>
  60
  61     <note>
  62       <title>Experimental</title>
  63
  64       <para>This is an <link linkend="experimental">experimental</link>
  65 interface and may change in the future.</para>
  66     </note>
  67
  68     <para>For driver debugging purposes these ioctls allow test
  69 applications to access hardware registers directly. Regular
  70 applications must not use them.</para>
  71
  72     <para>Since writing or even reading registers can jeopardize the
  73 system security, its stability and damage the hardware, both ioctls
  74 require superuser privileges. Additionally the Linux kernel must be
  75 compiled with the <constant>CONFIG_VIDEO_ADV_DEBUG</constant> option
  76 to enable these ioctls.</para>
  77
  78     <para>To write a register applications must initialize all fields
  79 of a &v4l2-dbg-register; except for <structfield>size</structfield> and call
  80 <constant>VIDIOC_DBG_S_REGISTER</constant> with a pointer to this
  81 structure. The <structfield>match.type</structfield> and
  82 <structfield>match.addr</structfield> or <structfield>match.name</structfield>
  83 fields select a chip on the TV
  84 card, the <structfield>reg</structfield> field specifies a register
  85 number and the <structfield>val</structfield> field the value to be
  86 written into the register.</para>
  87
  88     <para>To read a register applications must initialize the
  89 <structfield>match.type</structfield>,
  90 <structfield>match.addr</structfield> or <structfield>match.name</structfield> and
  91 <structfield>reg</structfield> fields, and call
  92 <constant>VIDIOC_DBG_G_REGISTER</constant> with a pointer to this
  93 structure. On success the driver stores the register value in the
  94 <structfield>val</structfield> field and the size (in bytes) of the
  95 value in <structfield>size</structfield>.</para>
  96
  97     <para>When <structfield>match.type</structfield> is
  98 <constant>V4L2_CHIP_MATCH_BRIDGE</constant>,
  99 <structfield>match.addr</structfield> selects the nth non-sub-device chip
 100 on the TV card.  The number zero always selects the host chip, &eg; the
 101 chip connected to the PCI or USB bus. You can find out which chips are
 102 present with the &VIDIOC-DBG-G-CHIP-INFO; ioctl.</para>
 103
 104     <para>When <structfield>match.type</structfield> is
 105 <constant>V4L2_CHIP_MATCH_SUBDEV</constant>,
 106 <structfield>match.addr</structfield> selects the nth sub-device.</para>
 107
 108     <para>These ioctls are optional, not all drivers may support them.
 109 However when a driver supports these ioctls it must also support
 110 &VIDIOC-DBG-G-CHIP-INFO;. Conversely it may support
 111 <constant>VIDIOC_DBG_G_CHIP_INFO</constant> but not these ioctls.</para>
 112
 113     <para><constant>VIDIOC_DBG_G_REGISTER</constant> and
 114 <constant>VIDIOC_DBG_S_REGISTER</constant> were introduced in Linux
 115 2.6.21, but their API was changed to the one described here in kernel 2.6.29.</para>
 116
 117     <para>We recommended the <application>v4l2-dbg</application>
 118 utility over calling these ioctls directly. It is available from the
 119 LinuxTV v4l-dvb repository; see <ulink
 120 url="https://linuxtv.org/repo/">https://linuxtv.org/repo/</ulink> for
 121 access instructions.</para>
 122
 123     <!-- Note for convenience vidioc-dbg-g-chip-info.sgml
 124          contains a duplicate of this table. -->
 125     <table pgwide="1" frame="none" id="v4l2-dbg-match">
 126       <title>struct <structname>v4l2_dbg_match</structname></title>
 127       <tgroup cols="4">
 128         &cs-ustr;
 129         <tbody valign="top">
 130           <row>
 131             <entry>__u32</entry>
 132             <entry><structfield>type</structfield></entry>
 133             <entry>See <xref linkend="chip-match-types" /> for a list of
 134 possible types.</entry>
 135           </row>
 136           <row>
 137             <entry>union</entry>
 138             <entry>(anonymous)</entry>
 139           </row>
 140           <row>
 141             <entry></entry>
 142             <entry>__u32</entry>
 143             <entry><structfield>addr</structfield></entry>
 144             <entry>Match a chip by this number, interpreted according
 145 to the <structfield>type</structfield> field.</entry>
 146           </row>
 147           <row>
 148             <entry></entry>
 149             <entry>char</entry>
 150             <entry><structfield>name[32]</structfield></entry>
 151             <entry>Match a chip by this name, interpreted according
 152 to the <structfield>type</structfield> field. Currently unused.</entry>
 153           </row>
 154         </tbody>
 155       </tgroup>
 156     </table>
 157
 158
 159     <table pgwide="1" frame="none" id="v4l2-dbg-register">
 160       <title>struct <structname>v4l2_dbg_register</structname></title>
 161       <tgroup cols="4">
 162         <colspec colname="c1" />
 163         <colspec colname="c2" />
 164         <colspec colname="c4" />
 165         <tbody valign="top">
 166           <row>
 167             <entry>struct v4l2_dbg_match</entry>
 168             <entry><structfield>match</structfield></entry>
 169             <entry>How to match the chip, see <xref linkend="v4l2-dbg-match" />.</entry>
 170           </row>
 171           <row>
 172             <entry>__u32</entry>
 173             <entry><structfield>size</structfield></entry>
 174             <entry>The register size in bytes.</entry>
 175           </row>
 176           <row>
 177             <entry>__u64</entry>
 178             <entry><structfield>reg</structfield></entry>
 179             <entry>A register number.</entry>
 180           </row>
 181           <row>
 182             <entry>__u64</entry>
 183             <entry><structfield>val</structfield></entry>
 184             <entry>The value read from, or to be written into the
 185 register.</entry>
 186           </row>
 187         </tbody>
 188       </tgroup>
 189     </table>
 190
 191     <!-- Note for convenience vidioc-dbg-g-chip-info.sgml
 192          contains a duplicate of this table. -->
 193     <table pgwide="1" frame="none" id="chip-match-types">
 194       <title>Chip Match Types</title>
 195       <tgroup cols="3">
 196         &cs-def;
 197         <tbody valign="top">
 198           <row>
 199             <entry><constant>V4L2_CHIP_MATCH_BRIDGE</constant></entry>
 200             <entry>0</entry>
 201             <entry>Match the nth chip on the card, zero for the
 202             bridge chip. Does not match sub-devices.</entry>
 203           </row>
 204           <row>
 205             <entry><constant>V4L2_CHIP_MATCH_SUBDEV</constant></entry>
 206             <entry>4</entry>
 207             <entry>Match the nth sub-device.</entry>
 208           </row>
 209         </tbody>
 210       </tgroup>
 211     </table>
 212   </refsect1>
 213
 214   <refsect1>
 215     &return-value;
 216
 217     <variablelist>
 218       <varlistentry>
 219         <term><errorcode>EPERM</errorcode></term>
 220         <listitem>
 221           <para>Insufficient permissions. Root privileges are required
 222 to execute these ioctls.</para>
 223         </listitem>
 224       </varlistentry>
 225     </variablelist>
 226   </refsect1>
 227 </refentry>