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>
65interface and may change in the future.</para>
66    </note>
67
68    <para>For driver debugging purposes these ioctls allow test
69applications to access hardware registers directly. Regular
70applications must not use them.</para>
71
72    <para>Since writing or even reading registers can jeopardize the
73system security, its stability and damage the hardware, both ioctls
74require superuser privileges. Additionally the Linux kernel must be
75compiled with the <constant>CONFIG_VIDEO_ADV_DEBUG</constant> option
76to enable these ioctls.</para>
77
78    <para>To write a register applications must initialize all fields
79of a &v4l2-dbg-register; and call
80<constant>VIDIOC_DBG_S_REGISTER</constant> with a pointer to this
81structure. The <structfield>match.type</structfield> and
82<structfield>match.addr</structfield> or <structfield>match.name</structfield>
83fields select a chip on the TV
84card, the <structfield>reg</structfield> field specifies a register
85number and the <structfield>val</structfield> field the value to be
86written into the register.</para>
87
88    <para>To read a register applications must initialize the
89<structfield>match.type</structfield>,
90<structfield>match.chip</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
93structure. On success the driver stores the register value in the
94<structfield>val</structfield> field. On failure the structure remains
95unchanged.</para>
96
97    <para>When <structfield>match.type</structfield> is
98<constant>V4L2_CHIP_MATCH_HOST</constant>,
99<structfield>match.addr</structfield> selects the nth non-&i2c; chip
100on the TV card.  The number zero always selects the host chip, &eg; the
101chip connected to the PCI or USB bus. You can find out which chips are
102present with the &VIDIOC-DBG-G-CHIP-IDENT; ioctl.</para>
103
104    <para>When <structfield>match.type</structfield> is
105<constant>V4L2_CHIP_MATCH_I2C_DRIVER</constant>,
106<structfield>match.name</structfield> contains the I2C driver name.
107For instance
108<constant>"saa7127"</constant> will match any chip
109supported by the saa7127 driver, regardless of its &i2c; bus address.
110When multiple chips supported by the same driver are present, the
111effect of these ioctls is undefined. Again with the
112&VIDIOC-DBG-G-CHIP-IDENT; ioctl you can find out which &i2c; chips are
113present.</para>
114
115    <para>When <structfield>match.type</structfield> is
116<constant>V4L2_CHIP_MATCH_I2C_ADDR</constant>,
117<structfield>match.addr</structfield> selects a chip by its 7 bit &i2c;
118bus address.</para>
119
120    <para>When <structfield>match.type</structfield> is
121<constant>V4L2_CHIP_MATCH_AC97</constant>,
122<structfield>match.addr</structfield> selects the nth AC97 chip
123on the TV card.</para>
124
125    <note>
126      <title>Success not guaranteed</title>
127
128      <para>Due to a flaw in the Linux &i2c; bus driver these ioctls may
129return successfully without actually reading or writing a register. To
130catch the most likely failure we recommend a &VIDIOC-DBG-G-CHIP-IDENT;
131call confirming the presence of the selected &i2c; chip.</para>
132    </note>
133
134    <para>These ioctls are optional, not all drivers may support them.
135However when a driver supports these ioctls it must also support
136&VIDIOC-DBG-G-CHIP-IDENT;. Conversely it may support
137<constant>VIDIOC_DBG_G_CHIP_IDENT</constant> but not these ioctls.</para>
138
139    <para><constant>VIDIOC_DBG_G_REGISTER</constant> and
140<constant>VIDIOC_DBG_S_REGISTER</constant> were introduced in Linux
1412.6.21, but their API was changed to the one described here in kernel 2.6.29.</para>
142
143    <para>We recommended the <application>v4l2-dbg</application>
144utility over calling these ioctls directly. It is available from the
145LinuxTV v4l-dvb repository; see <ulink
146url="http://linuxtv.org/repo/">http://linuxtv.org/repo/</ulink> for
147access instructions.</para>
148
149    <!-- Note for convenience vidioc-dbg-g-chip-ident.sgml
150	 contains a duplicate of this table. -->
151    <table pgwide="1" frame="none" id="v4l2-dbg-match">
152      <title>struct <structname>v4l2_dbg_match</structname></title>
153      <tgroup cols="4">
154	&cs-ustr;
155	<tbody valign="top">
156	  <row>
157	    <entry>__u32</entry>
158	    <entry><structfield>type</structfield></entry>
159	    <entry>See <xref linkend="ident-chip-match-types" /> for a list of
160possible types.</entry>
161	  </row>
162	  <row>
163	    <entry>union</entry>
164	    <entry>(anonymous)</entry>
165	  </row>
166	  <row>
167	    <entry></entry>
168	    <entry>__u32</entry>
169	    <entry><structfield>addr</structfield></entry>
170	    <entry>Match a chip by this number, interpreted according
171to the <structfield>type</structfield> field.</entry>
172	  </row>
173	  <row>
174	    <entry></entry>
175	    <entry>char</entry>
176	    <entry><structfield>name[32]</structfield></entry>
177	    <entry>Match a chip by this name, interpreted according
178to the <structfield>type</structfield> field.</entry>
179	  </row>
180	</tbody>
181      </tgroup>
182    </table>
183
184
185    <table pgwide="1" frame="none" id="v4l2-dbg-register">
186      <title>struct <structname>v4l2_dbg_register</structname></title>
187      <tgroup cols="4">
188	<colspec colname="c1" />
189	<colspec colname="c2" />
190	<colspec colname="c4" />
191	<tbody valign="top">
192	  <row>
193	    <entry>struct v4l2_dbg_match</entry>
194	    <entry><structfield>match</structfield></entry>
195	    <entry>How to match the chip, see <xref linkend="v4l2-dbg-match" />.</entry>
196	  </row>
197	  <row>
198	    <entry>__u64</entry>
199	    <entry><structfield>reg</structfield></entry>
200	    <entry>A register number.</entry>
201	  </row>
202	  <row>
203	    <entry>__u64</entry>
204	    <entry><structfield>val</structfield></entry>
205	    <entry>The value read from, or to be written into the
206register.</entry>
207	  </row>
208	</tbody>
209      </tgroup>
210    </table>
211
212    <!-- Note for convenience vidioc-dbg-g-chip-ident.sgml
213	 contains a duplicate of this table. -->
214    <table pgwide="1" frame="none" id="chip-match-types">
215      <title>Chip Match Types</title>
216      <tgroup cols="3">
217	&cs-def;
218	<tbody valign="top">
219	  <row>
220	    <entry><constant>V4L2_CHIP_MATCH_HOST</constant></entry>
221	    <entry>0</entry>
222	    <entry>Match the nth chip on the card, zero for the
223	    host chip. Does not match &i2c; chips.</entry>
224	  </row>
225	  <row>
226	    <entry><constant>V4L2_CHIP_MATCH_I2C_DRIVER</constant></entry>
227	    <entry>1</entry>
228	    <entry>Match an &i2c; chip by its driver name.</entry>
229	  </row>
230	  <row>
231	    <entry><constant>V4L2_CHIP_MATCH_I2C_ADDR</constant></entry>
232	    <entry>2</entry>
233	    <entry>Match a chip by its 7 bit &i2c; bus address.</entry>
234	  </row>
235	  <row>
236	    <entry><constant>V4L2_CHIP_MATCH_AC97</constant></entry>
237	    <entry>3</entry>
238	    <entry>Match the nth anciliary AC97 chip.</entry>
239	  </row>
240	</tbody>
241      </tgroup>
242    </table>
243  </refsect1>
244
245  <refsect1>
246    &return-value;
247
248    <variablelist>
249      <varlistentry>
250	<term><errorcode>EPERM</errorcode></term>
251	<listitem>
252	  <para>Insufficient permissions. Root privileges are required
253to execute these ioctls.</para>
254	</listitem>
255      </varlistentry>
256    </variablelist>
257  </refsect1>
258</refentry>
259