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V4L2 uses the enum type in IOCTL arguments in IOCTLs that were defined until the use of enum was considered less than ideal. Recently Rémi Denis-Courmont brought up the issue by proposing a patch to convert the enums to unsigned: <URL:http://www.spinics.net/lists/linux-media/msg46167.html> This sparked a long discussion where another solution to the issue was proposed: two sets of IOCTL structures, one with __u32 and the other with enums, and conversion code between the two: <URL:http://www.spinics.net/lists/linux-media/msg47168.html> Both approaches implement a complete solution that resolves the problem. The first one is simple but requires assuming enums and __u32 are the same in size (so we won't break the ABI) while the second one is more complex and less clean but does not require making that assumption. The issue boils down to whether enums are fundamentally different from __u32 or not, and can the former be substituted by the latter. During the discussion it was concluded that the __u32 has the same size as enums on all archs Linux is supported: it has not been shown that replacing those enums in IOCTL arguments would break neither source or binary compatibility. If no such reason is found, just replacing the enums with __u32s is the way to go. This is what this patch does. This patch is slightly different from Remi's first RFC (link above): it uses __u32 instead of unsigned and also changes the arguments of VIDIOC_G_PRIORITY and VIDIOC_S_PRIORITY. Signed-off-by: Rémi Denis-Courmont <remi@remlab.net> Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi> Acked-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
129 lines
3.9 KiB
XML
129 lines
3.9 KiB
XML
<refentry id="vidioc-s-hw-freq-seek">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_S_HW_FREQ_SEEK</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_S_HW_FREQ_SEEK</refname>
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<refpurpose>Perform a hardware frequency seek</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_hw_freq_seek
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*<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_S_HW_FREQ_SEEK</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>Start a hardware frequency seek from the current frequency.
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To do this applications initialize the <structfield>tuner</structfield>,
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<structfield>type</structfield>, <structfield>seek_upward</structfield>,
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<structfield>spacing</structfield> and
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<structfield>wrap_around</structfield> fields, and zero out the
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<structfield>reserved</structfield> array of a &v4l2-hw-freq-seek; and
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call the <constant>VIDIOC_S_HW_FREQ_SEEK</constant> ioctl with a pointer
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to this structure.</para>
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<para>This ioctl is supported if the <constant>V4L2_CAP_HW_FREQ_SEEK</constant> capability is set.</para>
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<table pgwide="1" frame="none" id="v4l2-hw-freq-seek">
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<title>struct <structname>v4l2_hw_freq_seek</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>tuner</structfield></entry>
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<entry>The tuner index number. This is the
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same value as in the &v4l2-input; <structfield>tuner</structfield>
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field and the &v4l2-tuner; <structfield>index</structfield> field.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>type</structfield></entry>
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<entry>The tuner type. This is the same value as in the
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&v4l2-tuner; <structfield>type</structfield> field. See <xref
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linkend="v4l2-tuner-type" /></entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>seek_upward</structfield></entry>
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<entry>If non-zero, seek upward from the current frequency, else seek downward.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>wrap_around</structfield></entry>
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<entry>If non-zero, wrap around when at the end of the frequency range, else stop seeking.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>spacing</structfield></entry>
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<entry>If non-zero, defines the hardware seek resolution in Hz. The driver selects the nearest value that is supported by the device. If spacing is zero a reasonable default value is used.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[7]</entry>
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<entry>Reserved for future extensions. Applications
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must set the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The <structfield>tuner</structfield> index is out of
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bounds, the wrap_around value is not supported or the value in the <structfield>type</structfield> field is
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wrong.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EAGAIN</errorcode></term>
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<listitem>
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<para>The ioctl timed-out. Try again.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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