Re: [PATCH v2 1/3] media: v4l: async: add helper API media_async_register_subdev()

[Sakari Ailus]

Hi Frank,

Thanks for the set.

On Thu, Feb 26, 2026 at 05:55:26PM -0500, Frank Li wrote:
> Add the helper API media_async_register_subdev(), which
> combines media_entity_pads_init(), v4l2_subdev_init_finalize(), and
> v4l2_async_register_subdev() into a single call.
> 
> Reduce code duplication and simplify error handling in drivers.

I appreciate your efforts to try to simplify registering a sensor
sub-device, but I'm not sure this gets far enough to make a notable
difference: the new function calls two functions typically needed and
requires the driver to implement a new one for registering a sub-device.

> 
> Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
> ---
>  drivers/media/v4l2-core/v4l2-async.c | 33 +++++++++++++++++++++++++++++++++
>  include/media/v4l2-async.h           | 22 ++++++++++++++++++++++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> index 1c08bba9ecb91f46b7479da613d6c1688d4b0b5c..e07173f566fbd8fa332b5e58be288e806b4c0482 100644
> --- a/drivers/media/v4l2-core/v4l2-async.c
> +++ b/drivers/media/v4l2-core/v4l2-async.c
> @@ -19,6 +19,7 @@
>  #include <linux/slab.h>
>  #include <linux/types.h>
>  
> +#include <media/media-entity.h>
>  #include <media/v4l2-async.h>
>  #include <media/v4l2-device.h>
>  #include <media/v4l2-fwnode.h>
> @@ -881,6 +882,38 @@ int __v4l2_async_register_subdev(struct v4l2_subdev *sd, struct module *module)
>  }
>  EXPORT_SYMBOL(__v4l2_async_register_subdev);
>  
> +int __media_pad_init_and_register_subdev(struct v4l2_subdev *sd, u16 num_pads,
> +	struct media_pad *pads,
> +	int (*register_subdev)(struct v4l2_subdev *sd, struct module *module),
> +	struct module *module)
> +{
> +	int ret;
> +
> +	if (!register_subdev)
> +		return -EINVAL;
> +
> +	ret = media_entity_pads_init(&sd->entity, num_pads, pads);
> +	if (ret)
> +		return ret;
> +
> +	ret = v4l2_subdev_init_finalize(sd);
> +	if (ret)
> +		goto err_entity_cleanup;
> +
> +	ret = register_subdev(sd, module);
> +	if (ret)
> +		goto err_subdev_cleanup;
> +
> +	return 0;
> +
> +err_subdev_cleanup:
> +	v4l2_subdev_cleanup(sd);
> +err_entity_cleanup:
> +	media_entity_cleanup(&sd->entity);
> +	return ret;
> +}
> +EXPORT_SYMBOL(__media_pad_init_and_register_subdev);
> +
>  void v4l2_async_unregister_subdev(struct v4l2_subdev *sd)
>  {
>  	struct v4l2_async_connection *asc, *asc_tmp;
> diff --git a/include/media/v4l2-async.h b/include/media/v4l2-async.h
> index f26c323e9c963065fd7c19d6d9835df1194bc069..220a302a626732e15452f3efb19b03bdc51e64d5 100644
> --- a/include/media/v4l2-async.h
> +++ b/include/media/v4l2-async.h
> @@ -336,6 +336,28 @@ int __v4l2_async_register_subdev(struct v4l2_subdev *sd, struct module *module);
>  int __must_check
>  v4l2_async_register_subdev_sensor(struct v4l2_subdev *sd);
>  
> +struct media_pad;
> +
> +int __must_check
> +__media_pad_init_and_register_subdev(struct v4l2_subdev *sd, u16 num_pads,
> +	struct media_pad *pads,
> +	int (*register_subdev)(struct v4l2_subdev *sd, struct module *module),
> +	struct module *module);
> +
> +/**
> + * media_async_register_subdev - Initialize the entity pads and
> + *				 registers a sub-device to the
> + *				 asynchronous subdevice framework
> + * @sd: pointer to &struct v4l2_subdev
> + * @num_pads: total number of sink and source pads
> + * @pads: Array of @num_pads pads.
> + *
> + * Returns an error on failure, 0 on success.
> + */
> +#define media_async_register_subdev(sd, num_pads, pads)			\
> +	__media_pad_init_and_register_subdev(sd, num_pads, pads,	\
> +					     __v4l2_async_register_subdev, \
> +					     THIS_MODULE)
>  /**
>   * v4l2_async_unregister_subdev - unregisters a sub-device to the asynchronous
>   *	subdevice framework
> 

-- 
Kind regards,

Sakari Ailus