Re: [PATCH v2] media: mali-c55: Require an enabled link to start a video node

[Jacopo Mondi <jacopo.mondi@ideasonboard.com>]

Hi David

On Tue, Nov 10, 2026 at 08:32:00AM +0000, David CARLIER wrote:
> Fair point, sorry for the shortcuts.
>
> > What does it mean "rather than through the graph" ?
> > enable_streams() is propagated by drivers along the pipeline by design
>
> Badly worded, sorry. I only meant that start_streaming() takes the
> resizer from cap_dev->rsz rather than from the remote end of an enabled
> link, so it enables it even with the link disabled.
>
> > Is this a typo ? From FR we can't go to the DS resizer.
>
> Not for data, no. I meant the media_pipeline_populate() walk: from the

Ah ok

> ISP source video pad it follows the immutable link into the DS resizer
> sink pad and, through the internal route, its source pad. A
> MUST_CONNECT on that pad would then fail FR only streaming with the DS
> link disabled.

This means (and reading Documentation/admin-guide/media/mali-c55.rst I
think it was intended) that if you link-enable the DS-pipe you will have to
start streaming on the DS capture node, otherwise streaming will never
start due to mali_c55_pipeline_ready() returning false ?

I wish I had a system with a DS pipe to test with.

What I'm after here: I'm trying to figure out if your change
introduces any requirement on how pipe have to be handled and if this
has any implication on how libcamera works on mali.

A use case is continous capture from DS while only taking seldom
pictures from FR. In this case I have to link both pipes, start both
of them and feed buffers continuously to DS and only sporadically to
FR. The key here is the requirement to call STREAMON on both capture
nodes if they're linked.

In other words, if you want to use both pipes you need to link both of them
and call STREAMON on both capture devices, even if in a session you will be
capturing from one of them.

I think it's fine and matches the documentation in mali-c55.rst and
the libcamera pipeline handler.

>
> Thanks for the reviews.
> Cheers.