Message-ID: <4D585450.2050900@gmail.com>
Date:	Sun, 13 Feb 2011 22:59:44 +0100
From:	Sylwester Nawrocki <snjw23@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	alsa-devel@...a-project.org, clemens@...isch.de,
	broonie@...nsource.wolfsonmicro.com,
	sakari.ailus@...well.research.nokia.com
Subject: Re: [PATCH v8 07/12] media: Entities, pads and links enumeration

Hi Laurent,

Please see my little comment below..

On 2011-01-27 13:30, Laurent Pinchart wrote:
> Create the following two ioctls and implement them at the media device
> level to enumerate entities, pads and links.
> 
> - MEDIA_IOC_ENUM_ENTITIES: Enumerate entities and their properties
> - MEDIA_IOC_ENUM_LINKS: Enumerate all pads and links for a given entity
> 
> Entity IDs can be non-contiguous. Userspace applications should
> enumerate entities using the MEDIA_ENT_ID_FLAG_NEXT flag. When the flag
> is set in the entity ID, the MEDIA_IOC_ENUM_ENTITIES will return the
> next entity with an ID bigger than the requested one.
> 
> Only forward links that originate at one of the entity's source pads are
> returned during the enumeration process.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Signed-off-by: Sakari Ailus <sakari.ailus@...well.research.nokia.com>
> ---
>  Documentation/DocBook/media-entities.tmpl          |    8 +
>  Documentation/DocBook/v4l/media-controller.xml     |    2 +
>  .../DocBook/v4l/media-ioc-device-info.xml          |    3 +-
>  .../DocBook/v4l/media-ioc-enum-entities.xml        |  308 ++++++++++++++++++++
>  Documentation/DocBook/v4l/media-ioc-enum-links.xml |  202 +++++++++++++
>  drivers/media/media-device.c                       |  123 ++++++++
>  include/linux/media.h                              |   85 ++++++
>  include/media/media-entity.h                       |   24 +--
>  8 files changed, 731 insertions(+), 24 deletions(-)
>  create mode 100644 Documentation/DocBook/v4l/media-ioc-enum-entities.xml
>  create mode 100644 Documentation/DocBook/v4l/media-ioc-enum-links.xml
> 
...
> diff --git a/Documentation/DocBook/v4l/media-ioc-enum-links.xml b/Documentation/DocBook/v4l/media-ioc-enum-links.xml
> new file mode 100644
> index 0000000..daf0360
> --- /dev/null
> +++ b/Documentation/DocBook/v4l/media-ioc-enum-links.xml
> @@ -0,0 +1,202 @@
> +<refentry id="media-ioc-enum-links">
> +  <refmeta>
> +    <refentrytitle>ioctl MEDIA_IOC_ENUM_LINKS</refentrytitle>
> +    &manvol;
> +  </refmeta>
> +
> +  <refnamediv>
> +    <refname>MEDIA_IOC_ENUM_LINKS</refname>
> +    <refpurpose>Enumerate all pads and links for a given entity</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 media_links_enum *<parameter>argp</parameter></paramdef>
> +      </funcprototype>
> +    </funcsynopsis>
> +  </refsynopsisdiv>
> +
> +  <refsect1>
> +    <title>Arguments</title>
> +
> +    <variablelist>
> +      <varlistentry>
> +	<term><parameter>fd</parameter></term>
> +	<listitem>
> +	  <para>File descriptor returned by
> +	  <link linkend='media-func-open'><function>open()</function></link>.</para>
> +	</listitem>
> +      </varlistentry>
> +      <varlistentry>
> +	<term><parameter>request</parameter></term>
> +	<listitem>
> +	  <para>MEDIA_IOC_ENUM_LINKS</para>
> +	</listitem>
> +      </varlistentry>
> +      <varlistentry>
> +	<term><parameter>argp</parameter></term>
> +	<listitem>
> +	  <para></para>
> +	</listitem>
> +      </varlistentry>
> +    </variablelist>
> +  </refsect1>
> +
> +  <refsect1>
> +    <title>Description</title>
> +
> +    <para>To enumerate pads and/or links for a given entity, applications set
> +    the entity field of a &media-links-enum; structure and initialize the
> +    &media-pad-desc; and &media-link-desc; structure arrays pointed by the
> +    <structfield>pads</structfield> and <structfield>links</structfield> fields.
> +    They then call the MEDIA_IOC_ENUM_LINKS ioctl with a pointer to this
> +    structure.</para>
> +    <para>If the <structfield>pads</structfield> field is not NULL, the driver
> +    fills the <structfield>pads</structfield> array with information about the
> +    entity's pads. The array must have enough room to store all the entity's
> +    pads. The number of pads can be retrieved with the &MEDIA-IOC-ENUM-ENTITIES;
> +    ioctl.</para>
> +    <para>If the <structfield>links</structfield> field is not NULL, the driver
> +    fills the <structfield>links</structfield> array with information about the
> +    entity's outbound links. The array must have enough room to store all the
> +    entity's outbound links. The number of outbound links can be retrieved with
> +    the &MEDIA-IOC-ENUM-ENTITIES; ioctl.</para>
> +    <para>Only forward links that originate at one of the entity's source pads
> +    are returned during the enumeration process.</para>
> +
> +    <table pgwide="1" frame="none" id="media-links-enum">
> +      <title>struct <structname>media_links_enum</structname></title>
> +      <tgroup cols="3">
> +        &cs-str;
> +	<tbody valign="top">
> +	  <row>
> +	    <entry>__u32</entry>
> +	    <entry><structfield>entity</structfield></entry>
> +	    <entry>Entity id, set by the application.</entry>
> +	  </row>
> +	  <row>
> +	    <entry>struct &media-pad-desc;</entry>
> +	    <entry>*<structfield>pads</structfield></entry>
> +	    <entry>Pointer to a pads array allocated by the application. Ignored
> +	    if NULL.</entry>
> +	  </row>
> +	  <row>
> +	    <entry>struct &media-link-desc;</entry>
> +	    <entry>*<structfield>links</structfield></entry>
> +	    <entry>Pointer to a links array allocated by the application. Ignored
> +	    if NULL.</entry>
> +	  </row>
> +	</tbody>
> +      </tgroup>
> +    </table>
> +
> +    <table pgwide="1" frame="none" id="media-pad-desc">
> +      <title>struct <structname>media_pad_desc</structname></title>
> +      <tgroup cols="3">
> +        &cs-str;
> +	<tbody valign="top">
> +	  <row>
> +	    <entry>__u32</entry>
> +	    <entry><structfield>entity</structfield></entry>
> +	    <entry>ID of the entity this pad belongs to.</entry>
> +	  </row>
> +	  <row>
> +	    <entry>__u16</entry>
> +	    <entry><structfield>index</structfield></entry>
> +	    <entry>0-based pad index.</entry>
> +	  </row>
> +	  <row>
> +	    <entry>__u32</entry>
> +	    <entry><structfield>flags</structfield></entry>
> +	    <entry>Pad flags, see <xref linkend="media-pad-flag" /> for more details.</entry>
> +	  </row>
> +	</tbody>
> +      </tgroup>
> +    </table>
> +
> +    <table frame="none" pgwide="1" id="media-pad-flag">
> +      <title>Media pad flags</title>
> +      <tgroup cols="2">
> +        <colspec colname="c1"/>
> +        <colspec colname="c2"/>
> +	<tbody valign="top">
> +	  <row>
> +	    <entry><constant>MEDIA_PAD_FL_INPUT</constant></entry>
> +	    <entry>Input pad, relative to the entity. Input pads sink data and
> +	    are targets of links.</entry>
> +	  </row>
> +	  <row>
> +	    <entry><constant>MEDIA_PAD_FL_OUTPUT</constant></entry>
> +	    <entry>Output pad, relative to the entity. Output pads source data
> +	    and are origins of links.</entry>
> +	  </row>
> +	</tbody>
> +      </tgroup>
> +    </table>
> +
> +    <table pgwide="1" frame="none" id="media-link-desc">
> +      <title>struct <structname>media_links_enum</structname></title>

..the above line should perhaps be:

> +      <title>struct <structname>media_links_desc</structname></title>

as "struct media_links_desc" is described above.

BTW, I was wondering how one makes use of the pads associated with
a media entity of type other than MEDIA_ENT_T_V4L2_SUBDEV*,
e.g. V4L2 device - MEDIA_ENT_T_DEVNODE_V4L.

I guess new standard ioctls should be added for per pads operations
at V4L2 device, similarly is it is done with v4l2-subdevs.
Is this right?


Regards,
Sylwester

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