[PATCH v5 2/8] media: v4l2-fwnode: Add common helper library for 1-to-1 subdev registration

[Sakari Ailus]

Hi Frank,

Thanks for the patch.

On Wed, Jun 17, 2026 at 03:50:12PM -0400, Frank.Li at oss.nxp.com wrote:
> From: Frank Li <Frank.Li at nxp.com>
> 
> Many V4L2 subdev drivers implement the same registration and media pad
> setup logic for simple pipelines consisting of a single sink pad and a
> single source pad. As a result, the same boilerplate code is duplicated
> across multiple drivers.
> 
> Introduce a common helper library for 1-to-1 subdevs to encapsulate the
> registration, media entity initialization, and cleanup paths. Drivers
> can embed a struct v4l2_subdev_1to1 instance and use the provided helper
> APIs instead of open-coding the setup sequence.

I appreciate your efforts in trying to reduce the amount of code drivers
need simply to get things done but I think there are a few issues with the
approach taken in this patch:

- The new helpers aren't generic enough, but require two pads; one sink,
  one source. You could provide special helpers for just this case, but
  right now it looks like that if there's something you need that the
  helper assumes you don't, you can't use the helper at all. In other
  words, more modularity would be nice.

- The new helper should work with the existing types and not add new types
  (struct v4l2_subdev_1to1).

- There should be a way to provide default V4L2 fwnode endpoint
  configuration as well as to validate the obtained configuration.

I don't have a good proposal to address the above but at least one way I
can think of making error handling easier would be to use devm_() for
teardown in more places we to today. That certainly does have its own
issues though.

-- 
Kind regards,

Sakari Ailus