Re: [PATCH v8 36/38] media: v4l: Add V4L2_SUBDEV_ROUTE_FL_IMMUTABLE sub-device routing flag

From: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
To: Sakari Ailus <sakari.ailus@linux.intel.com>, linux-media@vger.kernel.org
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	bingbu.cao@intel.com, hongju.wang@intel.com, hverkuil@xs4all.nl,
	Andrey Konovalov <andrey.konovalov@linaro.org>,
	Jacopo Mondi <jacopo.mondi@ideasonboard.com>,
	Dmitry Perchanov <dmitry.perchanov@intel.com>,
	"Ng, Khai Wen" <khai.wen.ng@intel.com>,
	Alain Volmat <alain.volmat@foss.st.com>
Subject: Re: [PATCH v8 36/38] media: v4l: Add V4L2_SUBDEV_ROUTE_FL_IMMUTABLE sub-device routing flag
Date: Wed, 13 Mar 2024 09:34:13 +0200	[thread overview]
Message-ID: <9265171e-b4a7-468e-83b4-51af5e8823dc@ideasonboard.com> (raw)
In-Reply-To: <20240313072516.241106-37-sakari.ailus@linux.intel.com>

On 13/03/2024 09:25, Sakari Ailus wrote:
> Add a flag to denote immutable routes, V4L2_SUBDEV_ROUTE_FL_IMMUTABLE.
> Such routes cannot be changed and they're always active.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>   Documentation/userspace-api/media/v4l/dev-subdev.rst         | 3 ++-
>   .../userspace-api/media/v4l/vidioc-subdev-g-routing.rst      | 5 +++++
>   include/uapi/linux/v4l2-subdev.h                             | 5 +++++
>   3 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst
> index 08495cc6f4a6..2f2423f676cf 100644
> --- a/Documentation/userspace-api/media/v4l/dev-subdev.rst
> +++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst
> @@ -572,7 +572,8 @@ 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.
> +on driver capabilities. This capatibility is indicated by the
> +:ref:`V4L2_SUBDEV_ROUTE_FL_IMMUTABLE <v4l2-subdev-routing-flags>` flag.
>   
>   Interaction between routes, streams, formats and selections
>   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
> index 08b8d17cef3f..cd7735f9104e 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
> @@ -139,6 +139,11 @@ Also ``VIDIOC_SUBDEV_S_ROUTING`` may return more route than the user provided in
>       * - V4L2_SUBDEV_ROUTE_FL_ACTIVE
>         - 0x0001
>         - The route is enabled. Set by applications.
> +    * - V4L2_SUBDEV_ROUTE_FL_IMMUTABLE
> +      - 0x0002
> +      - The route is immutable. Set by the driver. The
> +	``V4L2_SUBDEV_ROUTE_FL_ACTIVE`` flag of an immutable route may not be
> +	changed.
>   
>   Return Value
>   ============
> diff --git a/include/uapi/linux/v4l2-subdev.h b/include/uapi/linux/v4l2-subdev.h
> index ca543982460c..7e501cb45e4e 100644
> --- a/include/uapi/linux/v4l2-subdev.h
> +++ b/include/uapi/linux/v4l2-subdev.h
> @@ -200,6 +200,11 @@ struct v4l2_subdev_capability {
>    * on a video node.
>    */
>   #define V4L2_SUBDEV_ROUTE_FL_ACTIVE		(1U << 0)
> +/*
> + * Is the route immutable. The ACTIVE flag of an immutable route may not be
> + * changed.
> + */
> +#define V4L2_SUBDEV_ROUTE_FL_IMMUTABLE		(1U << 1)
>   
>   /**
>    * struct v4l2_subdev_route - A route inside a subdev

Is the route fully immutable? The sink/source stream ID cannot be 
changed (or any new fields we might come up with in the future)?

Hmm, or would a route with different stream IDs be a, well, different 
route...

The docs here only talk about the ACTIVE flag. Would 
V4L2_SUBDEV_ROUTE_FL_ALWAYS_ACTIVE be a better name, to be more explicit 
on the meaning?

  Tomi