Re: [PATCH v9 11/46] media: Documentation: Document S_ROUTING behaviour

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Hi Sakari,

Thank you for the patch.

On Tue, Apr 16, 2024 at 10:32:44PM +0300, Sakari Ailus wrote:
> Document S_ROUTING behaviour for different devices.
> 
> Generally in devices that produce streams the streams are static and some
> can be enabled and disabled, whereas in devices that just transport them
> or write them to memory, more configurability is allowed. Document this.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> Reviewed-by: Julien Massot <julien.massot@xxxxxxxxxxxxx>
> ---
>  .../userspace-api/media/v4l/dev-subdev.rst    | 24 +++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst
> index d30dcb9e2537..de8dfd4f11a5 100644
> --- a/Documentation/userspace-api/media/v4l/dev-subdev.rst
> +++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst
> @@ -593,6 +593,30 @@ Any configurations of a stream within a pad, such as format or selections,
>  are independent of similar configurations on other streams. This is
>  subject to change in the future.
>  
> +Device types and routing setup
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +Different kinds of sub-devices have differing behaviour for route activation,
> +depending on the hardware. In all cases, however, only routes that have the
> +``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set are active.
> +
> +Devices generating the streams may allow enabling and disabling some of the
> +routes or the configuration is fixed. If the routes can be disabled, not

"... some of the routes, or have a fixed routing configuration."

> +declaring the routes (or declaring them without
> +``VIDIOC_SUBDEV_STREAM_FL_ACTIVE`` flag set) in ``VIDIOC_SUBDEV_S_ROUTING`` will
> +disable the routes while the sub-device driver retains the streams and their
> +format and selection configuration.

I still find the "retains their format and selection configuration"
quite unclear :-S

> The ``VIDIOC_SUBDEV_S_ROUTING`` will still

s/will still/ioctl will still/

> +return such routes back to the user in the routes array, with the
> +``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag unset.
> +
> +Devices transporting the streams almost always have more configurability with
> +respect to routing. Typically any route between the sub-device's sink and source
> +pads is possible, and multiple routes (usually up to certain limited number) may
> +be active simultaneously. For such devices, no routes are created by the driver
> +and user-created routes are fully replaced when ``VIDIOC_SUBDEV_S_ROUTING`` is
> +called on the sub-device. Such newly created routes have the device's default
> +configuration for format and selection rectangles.
> +
>  Configuring streams
>  ^^^^^^^^^^^^^^^^^^^
>  

-- 
Regards,

Laurent Pinchart




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