Re: [PATCH v4 14/29] media: Documentation: Improve LINK_FREQ documentation

Laurent Pinchart
2026-04-16T15:05:09Z

On Wed, Apr 08, 2026 at 06:39:23PM +0300, Sakari Ailus wrote:
> Add a reference to the LINK_FREQ control and clarify the meaning of the
> control as for C-PHY the matter is less obvious.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> Reviewed-by: Mirela Rabulea <mirela.rabulea@nxp.com>
> Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
> ---
> Documentation/driver-api/media/tx-rx.rst | 3 ++-
> .../userspace-api/media/v4l/ext-ctrls-image-process.rst | 4 +++-
> 2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/driver-api/media/tx-rx.rst b/Documentation/driver-api/media/tx-rx.rst
> index 22e1b13ecde9..7df2407817b3 100644
> --- a/Documentation/driver-api/media/tx-rx.rst
> +++ b/Documentation/driver-api/media/tx-rx.rst
> @@ -93,7 +93,8 @@ where
> * - variable or constant
> - description
> * - link_freq
> - - The value of the ``V4L2_CID_LINK_FREQ`` integer64 menu item.
> + - The value of the :ref:`V4L2_CID_LINK_FREQ <v4l2-cid-link-freq>` integer64
> + menu item.
> * - nr_of_lanes
> - Number of data lanes used on the CSI-2 link.
> * - 2
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-image-process.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-image-process.rst
> index 6d516f041ca2..ee88933256dd 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-image-process.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-image-process.rst
> @@ -24,7 +24,9 @@ Image Process Control IDs
> .. _v4l2-cid-link-freq:
>
> ``V4L2_CID_LINK_FREQ (integer menu)``
> - The frequency of the data bus (e.g. parallel or CSI-2).
> + The fundamental frequency of the operating symbol rate (serial interfaces

While this is absolutely correct, I think it will confuse most readers
more than the existing text. Do you think that mentioning that, for
CSI-2, the frequency is equal to 1 / (2 * UI) would help ?

> + such as CSI-2) or the sampling rate (parallel interfaces such as DVP or
> + Bt.565) of the data interface.
>
> .. _v4l2-cid-pixel-rate:
>

--
Regards,

Laurent Pinchart