Re: [PATCH] media: v4l2-async: fix binding async subdevs with multiple source ports

[Philipp Zabel <p.zabel@pengutronix.de>]

Hi Laurent,

On Mon, Jan 16, 2023 at 03:08:27AM +0200, Laurent Pinchart wrote:
[...]
> To make sure I understand this correctly, you need both changes, with
> the change in __v4l2_async_nf_has_async_subdev() meant to address asds
> being added after the subdev has been registered, and the change in
> v4l2_async_register_subdev() meant to address asds that have been added
> before ?

Yes, your understanding is correct.

> The imx6 ipu drivers implement a "clever hack" to handle the
> multi-endpoint issue that was never officially supported by v4l2-async.

That belongs in parentheses all right. I think it might even have been
accidental.

> Obviously, as it has worked so far, leaving it broken isn't a very nice
> option. The fix feels a bit like a hack though, and a better solution
> would be to allow subdevs to be matched multiple times, by multiple
> consumers. That's a more intrusive change though, so I could be OK with
> this as a short term fix, assuming it doesn't break anything else.

Right, the intention was that this patch could be applied on stable
kernels, as I only had noticed the issue after the release.

> I would however want to ensure this doesn't get abused by new drivers.
> Could we add a dev_warn() somewhere to indicate that multi-endpoint
> matching is not supported and shouldn't be used until fixed ? Sakari,
> what do you think ?
[...]

pr_warn_once() in both places, perhaps?

regards
Philipp