Documentation/DocBook/media/v4l/vidioc-querycap.xml

   1 <refentry id="vidioc-querycap">
   2   <refmeta>
   3     <refentrytitle>ioctl VIDIOC_QUERYCAP</refentrytitle>
   4     &manvol;
   5   </refmeta>
   6
   7   <refnamediv>
   8     <refname>VIDIOC_QUERYCAP</refname>
   9     <refpurpose>Query device capabilities</refpurpose>
  10   </refnamediv>
  11
  12   <refsynopsisdiv>
  13     <funcsynopsis>
  14       <funcprototype>
  15         <funcdef>int <function>ioctl</function></funcdef>
  16         <paramdef>int <parameter>fd</parameter></paramdef>
  17         <paramdef>int <parameter>request</parameter></paramdef>
  18         <paramdef>struct v4l2_capability *<parameter>argp</parameter></paramdef>
  19       </funcprototype>
  20     </funcsynopsis>
  21   </refsynopsisdiv>
  22
  23   <refsect1>
  24     <title>Arguments</title>
  25
  26     <variablelist>
  27       <varlistentry>
  28         <term><parameter>fd</parameter></term>
  29         <listitem>
  30           <para>&fd;</para>
  31         </listitem>
  32       </varlistentry>
  33       <varlistentry>
  34         <term><parameter>request</parameter></term>
  35         <listitem>
  36           <para>VIDIOC_QUERYCAP</para>
  37         </listitem>
  38       </varlistentry>
  39       <varlistentry>
  40         <term><parameter>argp</parameter></term>
  41         <listitem>
  42           <para></para>
  43         </listitem>
  44       </varlistentry>
  45     </variablelist>
  46   </refsect1>
  47
  48   <refsect1>
  49     <title>Description</title>
  50
  51     <para>All V4L2 devices support the
  52 <constant>VIDIOC_QUERYCAP</constant> ioctl. It is used to identify
  53 kernel devices compatible with this specification and to obtain
  54 information about driver and hardware capabilities. The ioctl takes a
  55 pointer to a &v4l2-capability; which is filled by the driver. When the
  56 driver is not compatible with this specification the ioctl returns an
  57 &EINVAL;.</para>
  58
  59     <table pgwide="1" frame="none" id="v4l2-capability">
  60       <title>struct <structname>v4l2_capability</structname></title>
  61       <tgroup cols="3">
  62         &cs-str;
  63         <tbody valign="top">
  64           <row>
  65             <entry>__u8</entry>
  66             <entry><structfield>driver</structfield>[16]</entry>
  67             <entry><para>Name of the driver, a unique NUL-terminated
  68 ASCII string. For example: "bttv". Driver specific applications can
  69 use this information to verify the driver identity. It is also useful
  70 to work around known bugs, or to identify drivers in error reports.</para>
  71 <para>Storing strings in fixed sized arrays is bad
  72 practice but unavoidable here. Drivers and applications should take
  73 precautions to never read or write beyond the end of the array and to
  74 make sure the strings are properly NUL-terminated.</para></entry>
  75           </row>
  76           <row>
  77             <entry>__u8</entry>
  78             <entry><structfield>card</structfield>[32]</entry>
  79             <entry>Name of the device, a NUL-terminated ASCII string.
  80 For example: "Yoyodyne TV/FM". One driver may support different brands
  81 or models of video hardware. This information is intended for users,
  82 for example in a menu of available devices. Since multiple TV cards of
  83 the same brand may be installed which are supported by the same
  84 driver, this name should be combined with the character device file
  85 name (&eg; <filename>/dev/video2</filename>) or the
  86 <structfield>bus_info</structfield> string to avoid
  87 ambiguities.</entry>
  88           </row>
  89           <row>
  90             <entry>__u8</entry>
  91             <entry><structfield>bus_info</structfield>[32]</entry>
  92             <entry>Location of the device in the system, a
  93 NUL-terminated ASCII string. For example: "PCI:0000:05:06.0". This
  94 information is intended for users, to distinguish multiple
  95 identical devices. If no such information is available the field must
  96 simply count the devices controlled by the driver ("platform:vivi-000").
  97 The bus_info must start with "PCI:" for PCI boards, "PCIe:" for PCI Express boards,
  98 "usb-" for USB devices, "I2C:" for i2c devices, "ISA:" for ISA devices,
  99 "parport" for parallel port devices and "platform:" for platform devices.</entry>
 100           </row>
 101           <row>
 102             <entry>__u32</entry>
 103             <entry><structfield>version</structfield></entry>
 104             <entry><para>Version number of the driver.</para>
 105 <para>Starting on kernel 3.1, the version reported is provided per
 106 V4L2 subsystem, following the same Kernel numberation scheme. However, it
 107 should not always return the same version as the kernel, if, for example,
 108 an stable or distribution-modified kernel uses the V4L2 stack from a
 109 newer kernel.</para>
 110 <para>The version number is formatted using the
 111 <constant>KERNEL_VERSION()</constant> macro:</para></entry>
 112           </row>
 113           <row>
 114             <entry spanname="hspan"><para>
 115 <programlisting>
 116 #define KERNEL_VERSION(a,b,c) (((a) &lt;&lt; 16) + ((b) &lt;&lt; 8) + (c))
 117
 118 __u32 version = KERNEL_VERSION(0, 8, 1);
 119
 120 printf ("Version: %u.%u.%u\n",
 121         (version &gt;&gt; 16) &amp; 0xFF,
 122         (version &gt;&gt; 8) &amp; 0xFF,
 123          version &amp; 0xFF);
 124 </programlisting></para></entry>
 125           </row>
 126           <row>
 127             <entry>__u32</entry>
 128             <entry><structfield>capabilities</structfield></entry>
 129             <entry>Available capabilities of the physical device as a whole, see <xref
 130                 linkend="device-capabilities" />. The same physical device can export
 131                 multiple devices in /dev (e.g. /dev/videoX, /dev/vbiY and /dev/radioZ).
 132                 The <structfield>capabilities</structfield> field should contain a union
 133                 of all capabilities available around the several V4L2 devices exported
 134                 to userspace.
 135                 For all those devices the <structfield>capabilities</structfield> field
 136                 returns the same set of capabilities. This allows applications to open
 137                 just one of the devices (typically the video device) and discover whether
 138                 video, vbi and/or radio are also supported.
 139             </entry>
 140           </row>
 141           <row>
 142             <entry>__u32</entry>
 143             <entry><structfield>device_caps</structfield></entry>
 144             <entry>Device capabilities of the opened device, see <xref
 145                 linkend="device-capabilities" />. Should contain the available capabilities
 146                 of that specific device node. So, for example, <structfield>device_caps</structfield>
 147                 of a radio device will only contain radio related capabilities and
 148                 no video or vbi capabilities. This field is only set if the <structfield>capabilities</structfield>
 149                 field contains the <constant>V4L2_CAP_DEVICE_CAPS</constant> capability.
 150                 Only the <structfield>capabilities</structfield> field can have the
 151                 <constant>V4L2_CAP_DEVICE_CAPS</constant> capability, <structfield>device_caps</structfield>
 152                 will never set <constant>V4L2_CAP_DEVICE_CAPS</constant>.
 153             </entry>
 154           </row>
 155           <row>
 156             <entry>__u32</entry>
 157             <entry><structfield>reserved</structfield>[3]</entry>
 158             <entry>Reserved for future extensions. Drivers must set
 159 this array to zero.</entry>
 160           </row>
 161         </tbody>
 162       </tgroup>
 163     </table>
 164
 165     <table pgwide="1" frame="none" id="device-capabilities">
 166       <title>Device Capabilities Flags</title>
 167       <tgroup cols="3">
 168         &cs-def;
 169         <tbody valign="top">
 170           <row>
 171             <entry><constant>V4L2_CAP_VIDEO_CAPTURE</constant></entry>
 172             <entry>0x00000001</entry>
 173             <entry>The device supports the single-planar API through the <link
 174 linkend="capture">Video Capture</link> interface.</entry>
 175           </row>
 176           <row>
 177             <entry><constant>V4L2_CAP_VIDEO_CAPTURE_MPLANE</constant></entry>
 178             <entry>0x00001000</entry>
 179             <entry>The device supports the
 180             <link linkend="planar-apis">multi-planar API</link> through the
 181             <link linkend="capture">Video Capture</link> interface.</entry>
 182           </row>
 183           <row>
 184             <entry><constant>V4L2_CAP_VIDEO_OUTPUT</constant></entry>
 185             <entry>0x00000002</entry>
 186             <entry>The device supports the single-planar API through the <link
 187 linkend="output">Video Output</link> interface.</entry>
 188           </row>
 189           <row>
 190             <entry><constant>V4L2_CAP_VIDEO_OUTPUT_MPLANE</constant></entry>
 191             <entry>0x00002000</entry>
 192             <entry>The device supports the
 193             <link linkend="planar-apis">multi-planar API</link> through the
 194             <link linkend="output">Video Output</link> interface.</entry>
 195           </row>
 196           <row>
 197             <entry><constant>V4L2_CAP_VIDEO_M2M</constant></entry>
 198             <entry>0x00004000</entry>
 199             <entry>The device supports the single-planar API through the
 200             Video Memory-To-Memory interface.</entry>
 201           </row>
 202           <row>
 203             <entry><constant>V4L2_CAP_VIDEO_M2M_MPLANE</constant></entry>
 204             <entry>0x00008000</entry>
 205             <entry>The device supports the
 206             <link linkend="planar-apis">multi-planar API</link> through the
 207             Video Memory-To-Memory  interface.</entry>
 208           </row>
 209           <row>
 210             <entry><constant>V4L2_CAP_VIDEO_OVERLAY</constant></entry>
 211             <entry>0x00000004</entry>
 212             <entry>The device supports the <link
 213 linkend="overlay">Video Overlay</link> interface. A video overlay device
 214 typically stores captured images directly in the video memory of a
 215 graphics card, with hardware clipping and scaling.</entry>
 216           </row>
 217           <row>
 218             <entry><constant>V4L2_CAP_VBI_CAPTURE</constant></entry>
 219             <entry>0x00000010</entry>
 220             <entry>The device supports the <link linkend="raw-vbi">Raw
 221 VBI Capture</link> interface, providing Teletext and Closed Caption
 222 data.</entry>
 223           </row>
 224           <row>
 225             <entry><constant>V4L2_CAP_VBI_OUTPUT</constant></entry>
 226             <entry>0x00000020</entry>
 227             <entry>The device supports the <link linkend="raw-vbi">Raw VBI Output</link> interface.</entry>
 228           </row>
 229           <row>
 230             <entry><constant>V4L2_CAP_SLICED_VBI_CAPTURE</constant></entry>
 231             <entry>0x00000040</entry>
 232             <entry>The device supports the <link linkend="sliced">Sliced VBI Capture</link> interface.</entry>
 233           </row>
 234           <row>
 235             <entry><constant>V4L2_CAP_SLICED_VBI_OUTPUT</constant></entry>
 236             <entry>0x00000080</entry>
 237             <entry>The device supports the <link linkend="sliced">Sliced VBI Output</link> interface.</entry>
 238           </row>
 239           <row>
 240             <entry><constant>V4L2_CAP_RDS_CAPTURE</constant></entry>
 241             <entry>0x00000100</entry>
 242             <entry>The device supports the <link linkend="rds">RDS</link> capture interface.</entry>
 243           </row>
 244           <row>
 245             <entry><constant>V4L2_CAP_VIDEO_OUTPUT_OVERLAY</constant></entry>
 246             <entry>0x00000200</entry>
 247             <entry>The device supports the <link linkend="osd">Video
 248 Output Overlay</link> (OSD) interface. Unlike the <wordasword>Video
 249 Overlay</wordasword> interface, this is a secondary function of video
 250 output devices and overlays an image onto an outgoing video signal.
 251 When the driver sets this flag, it must clear the
 252 <constant>V4L2_CAP_VIDEO_OVERLAY</constant> flag and vice
 253 versa.<footnote><para>The &v4l2-framebuffer; lacks an
 254 &v4l2-buf-type; field, therefore the type of overlay is implied by the
 255 driver capabilities.</para></footnote></entry>
 256           </row>
 257           <row>
 258             <entry><constant>V4L2_CAP_HW_FREQ_SEEK</constant></entry>
 259             <entry>0x00000400</entry>
 260             <entry>The device supports the &VIDIOC-S-HW-FREQ-SEEK; ioctl for
 261 hardware frequency seeking.</entry>
 262           </row>
 263           <row>
 264             <entry><constant>V4L2_CAP_RDS_OUTPUT</constant></entry>
 265             <entry>0x00000800</entry>
 266             <entry>The device supports the <link linkend="rds">RDS</link> output interface.</entry>
 267           </row>
 268           <row>
 269             <entry><constant>V4L2_CAP_TUNER</constant></entry>
 270             <entry>0x00010000</entry>
 271             <entry>The device has some sort of tuner to
 272 receive RF-modulated video signals. For more information about
 273 tuner programming see
 274 <xref linkend="tuner" />.</entry>
 275           </row>
 276           <row>
 277             <entry><constant>V4L2_CAP_AUDIO</constant></entry>
 278             <entry>0x00020000</entry>
 279             <entry>The device has audio inputs or outputs. It may or
 280 may not support audio recording or playback, in PCM or compressed
 281 formats. PCM audio support must be implemented as ALSA or OSS
 282 interface. For more information on audio inputs and outputs see <xref
 283                 linkend="audio" />.</entry>
 284           </row>
 285           <row>
 286             <entry><constant>V4L2_CAP_RADIO</constant></entry>
 287             <entry>0x00040000</entry>
 288             <entry>This is a radio receiver.</entry>
 289           </row>
 290           <row>
 291             <entry><constant>V4L2_CAP_MODULATOR</constant></entry>
 292             <entry>0x00080000</entry>
 293             <entry>The device has some sort of modulator to
 294 emit RF-modulated video/audio signals. For more information about
 295 modulator programming see
 296 <xref linkend="tuner" />.</entry>
 297           </row>
 298           <row>
 299             <entry><constant>V4L2_CAP_READWRITE</constant></entry>
 300             <entry>0x01000000</entry>
 301             <entry>The device supports the <link
 302 linkend="rw">read()</link> and/or <link linkend="rw">write()</link>
 303 I/O methods.</entry>
 304           </row>
 305           <row>
 306             <entry><constant>V4L2_CAP_ASYNCIO</constant></entry>
 307             <entry>0x02000000</entry>
 308             <entry>The device supports the <link
 309 linkend="async">asynchronous</link> I/O methods.</entry>
 310           </row>
 311           <row>
 312             <entry><constant>V4L2_CAP_STREAMING</constant></entry>
 313             <entry>0x04000000</entry>
 314             <entry>The device supports the <link
 315 linkend="mmap">streaming</link> I/O method.</entry>
 316           </row>
 317           <row>
 318             <entry><constant>V4L2_CAP_DEVICE_CAPS</constant></entry>
 319             <entry>0x80000000</entry>
 320             <entry>The driver fills the <structfield>device_caps</structfield>
 321             field. This capability can only appear in the <structfield>capabilities</structfield>
 322             field and never in the <structfield>device_caps</structfield> field.</entry>
 323           </row>
 324         </tbody>
 325       </tgroup>
 326     </table>
 327   </refsect1>
 328
 329   <refsect1>
 330     &return-value;
 331   </refsect1>
 332 </refentry>