[media] v4l: v4l2_subdev userspace format API

Add a userspace API to get, set and enumerate the media format on a
subdev pad.

The format at the output of a subdev usually depends on the format at
its input(s). The try format operation is thus not suitable for probing
format at individual pads, as it can't modify the device state and thus
can't remember the format tried at the input to compute the output
format.

To fix the problem, pass an extra argument to the get/set format
operations to select the 'try' or 'active' format.

The try format is used when probing the subdev. Setting the try format
must not change the device configuration but can store data for later
reuse. Data storage is provided at the file-handle level so applications
probing the subdev concurently won't interfere with each other.

The active format is used when configuring the subdev. It's identical to
the format handled by the usual get/set operations.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Stanimir Varbanov <svarbanov@mm-sol.com>
Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 180 insertions, 0 deletions

diff --git a/Documentation/DocBook/v4l/vidioc-subdev-g-fmt.xml b/Documentation/DocBook/v4l/vidioc-subdev-g-fmt.xml
new file mode 100644
index 0000000..f367c57
--- /dev/null
+++ b/Documentation/DocBook/v4l/vidioc-subdev-g-fmt.xml
@@ -0,0 +1,180 @@
+<refentry id="vidioc-subdev-g-fmt">
+  <refmeta>
+    <refentrytitle>ioctl VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT</refentrytitle>
+    &manvol;
+  </refmeta>
+
+  <refnamediv>
+    <refname>VIDIOC_SUBDEV_G_FMT</refname>
+    <refname>VIDIOC_SUBDEV_S_FMT</refname>
+    <refpurpose>Get or set the data format on a subdev pad</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_subdev_format *<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_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT</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>These ioctls are used to negotiate the frame format at specific
+    subdev pads in the image pipeline.</para>
+
+    <para>To retrieve the current format applications set the
+    <structfield>pad</structfield> field of a &v4l2-subdev-format; to the
+    desired pad number as reported by the media API and the
+    <structfield>which</structfield> field to
+    <constant>V4L2_SUBDEV_FORMAT_ACTIVE</constant>. When they call the
+    <constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl with a pointer to this
+    structure the driver fills the members of the <structfield>format</structfield>
+    field.</para>
+
+    <para>To change the current format applications set both the
+    <structfield>pad</structfield> and <structfield>which</structfield> fields
+    and all members of the <structfield>format</structfield> field. When they
+    call the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl with a pointer to this
+    structure the driver verifies the requested format, adjusts it based on the
+    hardware capabilities and configures the device. Upon return the
+    &v4l2-subdev-format; contains the current format as would be returned by a
+    <constant>VIDIOC_SUBDEV_G_FMT</constant> call.</para>
+
+    <para>Applications can query the device capabilities by setting the
+    <structfield>which</structfield> to
+    <constant>V4L2_SUBDEV_FORMAT_TRY</constant>. When set, 'try' formats are not
+    applied to the device by the driver, but are changed exactly as active
+    formats and stored in the sub-device file handle. Two applications querying
+    the same sub-device would thus not interact with each other.</para>
+
+    <para>For instance, to try a format at the output pad of a sub-device,
+    applications would first set the try format at the sub-device input with the
+    <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl. They would then either
+    retrieve the default format at the output pad with the
+    <constant>VIDIOC_SUBDEV_G_FMT</constant> ioctl, or set the desired output
+    pad format with the <constant>VIDIOC_SUBDEV_S_FMT</constant> ioctl and check
+    the returned value.</para>
+
+    <para>Try formats do not depend on active formats, but can depend on the
+    current links configuration or sub-device controls value. For instance, a
+    low-pass noise filter might crop pixels at the frame boundaries, modifying
+    its output frame size.</para>
+
+    <para>Drivers must not return an error solely because the requested format
+    doesn't match the device capabilities. They must instead modify the format
+    to match what the hardware can provide. The modified format should be as
+    close as possible to the original request.</para>
+
+    <table pgwide="1" frame="none" id="v4l2-subdev-format">
+      <title>struct <structname>v4l2_subdev_format</structname></title>
+      <tgroup cols="3">
+        &cs-str;
+	<tbody valign="top">
+	  <row>
+	    <entry>__u32</entry>
+	    <entry><structfield>pad</structfield></entry>
+	    <entry>Pad number as reported by the media controller API.</entry>
+	  </row>
+	  <row>
+	    <entry>__u32</entry>
+	    <entry><structfield>which</structfield></entry>
+	    <entry>Format to modified, from &v4l2-subdev-format-whence;.</entry>
+	  </row>
+	  <row>
+	    <entry>&v4l2-mbus-framefmt;</entry>
+	    <entry><structfield>format</structfield></entry>
+	    <entry>Definition of an image format, see <xref
+	    linkend="v4l2-mbus-framefmt" /> for details.</entry>
+	  </row>
+	  <row>
+	    <entry>__u32</entry>
+	    <entry><structfield>reserved</structfield>[8]</entry>
+	    <entry>Reserved for future extensions. Applications and drivers must
+	    set the array to zero.</entry>
+	  </row>
+	</tbody>
+      </tgroup>
+    </table>
+
+    <table pgwide="1" frame="none" id="v4l2-subdev-format-whence">
+      <title>enum <structname>v4l2_subdev_format_whence</structname></title>
+      <tgroup cols="3">
+        &cs-def;
+	<tbody valign="top">
+	  <row>
+	    <entry>V4L2_SUBDEV_FORMAT_TRY</entry>
+	    <entry>0</entry>
+	    <entry>Try formats, used for querying device capabilities.</entry>
+	  </row>
+	  <row>
+	    <entry>V4L2_SUBDEV_FORMAT_ACTIVE</entry>
+	    <entry>1</entry>
+	    <entry>Active formats, applied to the hardware.</entry>
+	  </row>
+	</tbody>
+      </tgroup>
+    </table>
+  </refsect1>
+
+  <refsect1>
+    &return-value;
+
+    <variablelist>
+      <varlistentry>
+	<term><errorcode>EBUSY</errorcode></term>
+	<listitem>
+	  <para>The format can't be changed because the pad is currently busy.
+	  This can be caused, for instance, by an active video stream on the
+	  pad. The ioctl must not be retried without performing another action
+	  to fix the problem first. Only returned by
+	  <constant>VIDIOC_SUBDEV_S_FMT</constant></para>
+	</listitem>
+      </varlistentry>
+      <varlistentry>
+	<term><errorcode>EINVAL</errorcode></term>
+	<listitem>
+	  <para>The &v4l2-subdev-format; <structfield>pad</structfield>
+	  references a non-existing pad, or the <structfield>which</structfield>
+	  field references a non-existing format.</para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+</refentry>