Re: [PATCH 05/37] drm/display: bridge-connector: split code creating the connector to a subfunction

[Maxime Ripard]

On Fri, Jun 26, 2026 at 04:16:39PM +0200, Luca Ceresoli wrote:
> Hi Maxime,
> 
> On Fri Jun 26, 2026 at 12:09 PM CEST, Maxime Ripard wrote:
> > On Wed, Jun 24, 2026 at 05:47:10PM +0200, Luca Ceresoli wrote:
> >> On Wed Jun 24, 2026 at 1:41 PM CEST, Maxime Ripard wrote:
> >> > Hi,x
> >> >
> >> > On Fri, Jun 12, 2026 at 02:56:24PM +0200, Luca Ceresoli wrote:
> >> >> On Mon Jun 8, 2026 at 1:40 PM CEST, Maxime Ripard wrote:
> >> >> > On Tue, May 19, 2026 at 12:37:22PM +0200, Luca Ceresoli wrote:
> >> >> >> In preparation to introduce bridge hotplug, split out from
> >> >> >> drm_bridge_connector_init() the code adding the drm_connector into a
> >> >> >> dedicated function. This will be needed to be able to add (and re-add) the
> >> >> >> connector from different code paths.
> >> >> >
> >> >> > Same story here, explaining what you need later on that calls for that
> >> >> > change would be nice.
> >> >>
> >> >> Here's a more verbose version:
> >> >>
> >> >>     Currently drm_bridge_connector_init() does two things:
> >> >>
> >> >>      * allocate and initialize the drm_bridge_connector
> >> >>        (which embeds a drm_connector)
> >> >>      * initialize and register the embedded drm_connector
> >> >>
> >> >>     For bridge hotplug we need to separate these two actions:
> >> >>
> >> >>      * the drm_connector needs to be added and removed at any time based on
> >> >>        hotplug events
> >> >>      * the drm_bridge_connector is designated to create and remove the
> >> >>        drm_connector, so it must be persistent for the card lifetime
> >> >>
> >> >>     As the lifetimes of drm_bridge_connector and drm_connector become
> >> >>     different, we need to create them in different moments.
> >> >>
> >> >>     In preparation to support that, split out from
> >> >>     drm_bridge_connector_init() the code adding the drm_connector into a
> >> >>     dedicated function. No functional changes, just moving code around for
> >> >>     now. A future commit will make the drm_connector be created based on
> >> >>     hotplug events.
> >> >>
> >> >> Looks good?
> >> >
> >> > The message itself, yes, thanks.
> >> >
> >> > However, I have questions now :)
> >> >
> >> > Do we really expect drm_bridge_connector to stick around when a bridge
> >> > gets unplugged? If so, how does it cope with having, say, an HDMI
> >> > connector, and then swapping out the hotplugged part for an LVDS one?
> >> > Does the HDMI connector sticks around indefinitely?
> >>
> >> In your example, the HDMI drm_connector would be unregistered and put on
> >> hotunplug. Its allocation will stick around until the last put but that's
> >> quite irrelevant. Then, on plugging the LVDS addon, a new LVDS
> >> drm_connector will be created and registered.
> >>
> >> > *Especially* if we're using overlays for this, I'd expect everything
> >> >  after the first hotplugged bridge to be destroyed, no?
> >>
> >> As said, it would be unregistered immediately but might be freed later on
> >> if still refcounted.
> >>
> >> This is visible in patches 36+15, the path to follow is:
> >>
> >>  drm_bridge_connector_handle_event(event = DRM_BRIDGE_DETACHED) [patch 36]
> >>  -> drm_bridge_connector_dynconn_release()                      [patch 15]
> >>
> >> Does this solve your concern?
> >
> > Not really, I'm talking about drm_bridge_connector. The fact that
> > bridges are destroyed make sense to me. The fact that
> > drm_bridge_connector sticks around doesn't. It's supposed to be a
> > connector for bridges. If you don't have bridges because they got
> > destroyed, and connector, drm_bridge_connector doesn't have a reason to
> > exist anymore, unless it's drm_bridge_hotplug in a trench coat :)
> 
> It is not a hotplug-bridge in a trench coat, no :) The code is clear about
> this.
> 
> I'd say with this series a "drm_bridge_connector" is just becoming
> something more (perhaps something else too). Somewhat as "a drm_bridge is
> either a bridge or something else". :)
> 
> 
> But let's leave names aside for a moment. If just looking at the current
> code, the drm_bridge_connector is "a handler, owned by the card/encoder and
> having the same lifetime, which takes care of drm_connector
> creation/destruction at card probe/removal".
>
> What we need now is just the same plug " and on hotplug events" appended.
> 
> So in both cases there needs to be "a handler persitent with the card".
> 
> Do we agree so far?

Ish. If we go for that, then we need to update the name.
drm_bridge_connector for something that is neither a bridge or a
connector is not great.

But even then, I'm not even sure why we need to have that "manager" in
the first place. You want to make bridges be aware if they are the last
in the chain or not. Use that property in attach to either create a
drm_bridge_connector instance if you're last, or attach the next bridge
if you aren't.

And when a bridge is removed, drop everything after it in the chain,
drm_bridge_connector instance included.

And the encoder can take care of handling bridge remove and tearing down
the bridge chain itself.

Maximex

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