Re: [PATCH v8 09/38] media: Documentation: v4l: Document internal source pads

[Julien Massot <julien.massot@collabora.com>]

Hi Sakari,
On 3/19/24 14:47, Sakari Ailus wrote:
> Hi Julien,
> 
> On Fri, Mar 15, 2024 at 04:32:59PM +0100, Julien Massot wrote:
>>
>>
>> On 3/13/24 08:24, Sakari Ailus wrote:
>>> Document internal source pads, pads that have both SINK and INTERNAL flags
>>> set. Use the IMX219 camera sensor as an example.
>>>
>>> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
>>> ---
>>>    .../userspace-api/media/v4l/dev-subdev.rst    | 145 ++++++++++++++++++
>>>    1 file changed, 145 insertions(+)
>>>
>>> diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst
>>> index a387e8a15b8d..1808f40f63e3 100644
>>> --- a/Documentation/userspace-api/media/v4l/dev-subdev.rst
>>> +++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst
>>> @@ -553,6 +553,27 @@ A stream at a specific point in the media pipeline is identified by the
>>>    sub-device and a (pad, stream) pair. For sub-devices that do not support
>>>    multiplexed streams the 'stream' field is always 0.
>>> +.. _v4l2-subdev-internal-source-pads:
>>> +
>>> +Internal source pads and routing
>>> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>> +
>>> +Cases where a single sub-device source pad is traversed by multiple streams, one
>>> +or more of which originate from within the sub-device itself, are special as
>>> +there is no external sink pad for such routes. In those cases, the sources of
>>> +the internally generated streams are represented by internal source pads, which
>>> +are sink pads that have the :ref:`MEDIA_PAD_FL_INTERNAL <MEDIA-PAD-FL-INTERNAL>`
>>> +pad flag set.
>>> +
>>> +Internal pads have all the properties of an external pad, including formats and
>>> +selections. The format in this case is the source format of the stream. An
>>> +internal pad always has a single stream only (0).
>>> +
>>> +Routes from an internal source pad to an external source pad are typically not
>>> +modifiable but they can be activated and deactivated using the
>>> +:ref:`V4L2_SUBDEV_ROUTE_FL_ACTIVE <v4l2-subdev-routing-flags>` flag, depending
>>> +on driver capabilities.
>>> +
>>>    Interaction between routes, streams, formats and selections
>>>    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>> @@ -668,3 +689,127 @@ To configure this pipeline, the userspace must take the following steps:
>>>       the configurations along the stream towards the receiver, using
>>>       :ref:`VIDIOC_SUBDEV_S_FMT <VIDIOC_SUBDEV_G_FMT>` ioctls to configure each
>>>       stream endpoint in each sub-device.
>>> +
>>> +Internal pads setup example
>>> +^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>> +
>>> +A simple example of a multiplexed stream setup might be as follows:
>>> +
>>> +- An IMX219 camera sensor source sub-device, with one sink pad (0), one source pad
>>> +  (1), an internal sink pad (2) that represents the source of embedded
>> The pixel pad is an internal pad as well ?
> 
> How about:
> 
> - An IMX219 camera sensor source sub-device, with one internal sink pad
>    (0) for image data, one source pad (1), an internal sink pad (2) that
>    represents the source of embedded
sure looks good to me!

>   
>>
>>> +  data. There are two routes, one from the sink pad to the source, and another
>>> +  from the internal sink pad to the source pad. Both streams are always active,
>>> +  i.e. there is no need to separately enable the embedded data stream. The
>>> +  sensor uses the CSI-2 bus.
>>> +
>>> +- A CSI-2 receiver in the SoC (Receiver). The receiver has a single sink pad
>>> +  (pad 0), connected to the bridge, and two source pads (pads 1-2), going to the
>>> +  DMA engine. The receiver demultiplexes the incoming streams to the source
>>> +  pads.
>>> +
>>> +- DMA Engines in the SoC (DMA Engine), one for each stream. Each DMA engine is
>>> +  connected to a single source pad in the receiver.
>>> +
>>> +The sensor, the bridge and the receiver are modeled as V4L2 sub-devices,
>>> +exposed to userspace via /dev/v4l-subdevX device nodes. The DMA engines are
>>> +modeled as V4L2 devices, exposed to userspace via /dev/videoX nodes.
>>> +
>>> +To configure this pipeline, the userspace must take the following steps:
>>> +
>>> +1) Set up media links between entities: connect the sensors to the bridge,
>>> +   bridge to the receiver, and the receiver to the DMA engines. This step does
>>> +   not differ from normal non-multiplexed media controller setup.
>>> +
>>> +2) Configure routing
>>> +
>>> +.. flat-table:: Camera sensor. There are no configurable routes.
>>> +    :header-rows: 1
>>> +
>>> +    * - Sink Pad/Stream
>>> +      - Source Pad/Stream
>>> +      - Routing Flags
>>> +      - Comments
>>> +    * - 0/0
>>> +      - 1/0
>> - 1/0
>> - 0/0
>>> +      - V4L2_SUBDEV_ROUTE_FL_ACTIVE
>>> +      - Pixel data stream from the sink pad
>>> +    * - 2/0
>>> +      - 1/1
>> - 0/1
>>> +      - V4L2_SUBDEV_ROUTE_FL_ACTIVE
>>> +      - Metadata stream from the internal sink pad
>>
>> In latest patch "[PATCH v6 05/15] media: i2c: imx219: Add embedded data
>> support"
>> we have:
>> - 0 -> source pad
>> - 1 -> pixel/image
>> - 2 -> EDATA
>>
>> This is also what you did for ov2740.
> 
> Yes, these were leftovers from the CCS example. I've fixed them.
> 
>>
>> With that fixed:
>> Reviewed-by Julien Massot <julien.massot@collabora.com>
> 
> Thank you!
>