Re: [PATCH v7 2/5] media: v4l: Support obtaining link frequency via get_mbus_config

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sakari,

Thank you for the patch.

On Tue, Dec 10, 2024 at 09:59:03AM +0200, Sakari Ailus wrote:
> Add link_freq field to struct v4l2_mbus_config in order to pass the link
> frequency to the receiving sub-device.

The documentation of v4l2_get_link_freq() should be expanded to explain
the new mode of operation. It should document which of the supported
methods are recommended for new drivers.

> 
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  drivers/media/v4l2-core/v4l2-common.c | 11 ++++++++---
>  include/media/v4l2-mediabus.h         |  2 ++
>  2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index 9fe74c7e064f..88fbd5608f00 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -508,13 +508,18 @@ EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_ctrl);
>  s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
>  			     unsigned int div)
>  {
> +	struct v4l2_mbus_config mbus_config = {};

Isn't mbus_config fully populated by the .get_mbus_config() operation ?
That should be documented in the .get_mbus_config() operation
documentation.

>  	struct v4l2_subdev *sd;
> +	int ret;
>  
>  	sd = media_entity_to_v4l2_subdev(pad->entity);
> -	if (!sd)
> -		return -ENODEV;
> +	ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index,
> +			       &mbus_config);
> +	if (ret < 0 && ret != -ENOIOCTLCMD)
> +		return ret;
>  
> -	return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);
> +	return mbus_config.link_freq ?:
> +		__v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);

	if (mbus_config.link_freq)
		return mbus_config.link_freq;

	return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);

I wonder if we should also add a message in case link_freq is 0, to get
drivers to convert to reporting the link frequency through
.get_mbus_config() if they already implement the operation.

>  }
>  EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad);
>  #endif /* CONFIG_MEDIA_CONTROLLER */
> diff --git a/include/media/v4l2-mediabus.h b/include/media/v4l2-mediabus.h
> index 5bce6e423e94..cc5f776dc662 100644
> --- a/include/media/v4l2-mediabus.h
> +++ b/include/media/v4l2-mediabus.h
> @@ -148,6 +148,7 @@ enum v4l2_mbus_type {
>  /**
>   * struct v4l2_mbus_config - media bus configuration
>   * @type: interface type
> + * @link_freq: The link frequency. See also V4L2_CID_LINK_FREQ control.

Not a candidate for this series, but I'd like to simplify drivers by
implementing the LINK_FREQ control automatically.

>   * @bus: bus configuration data structure
>   * @bus.parallel: embedded &struct v4l2_mbus_config_parallel.
>   *		  Used if the bus is parallel or BT.656.
> @@ -162,6 +163,7 @@ enum v4l2_mbus_type {
>   */
>  struct v4l2_mbus_config {
>  	enum v4l2_mbus_type type;
> +	u64 link_freq;
>  	union {
>  		struct v4l2_mbus_config_parallel parallel;
>  		struct v4l2_mbus_config_mipi_csi1 mipi_csi1;

-- 
Regards,

Laurent Pinchart