Date:	Mon, 14 Feb 2011 13:11:48 +0100
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Sylwester Nawrocki <snjw23@...il.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 Sylwester,

On Sunday 13 February 2011 22:59:44 Sylwester Nawrocki wrote:
> 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.

Thanks for catching this. I'll fix it.

> 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?

I don't think we need now ioctls there. As DEVNODE_V4L entities are just an 
interface between the driver and userspace, applications should use V4L2 
ioctls on the video device node.

For non-V4L entities other ioctls will obviously be needed, but they will be 
defined by other subsystems such as ALSA (provided the entities have a device 
node).

-- 
Regards,

Laurent Pinchart
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