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

Tue Jul 7 05:32:05 PDT 2026

On Tue, Jul 07, 2026 at 11:55:54AM +0200, Maxime Ripard wrote:
> On Fri, Jun 26, 2026 at 06:51:14PM +0200, Luca Ceresoli wrote:
> > On Fri Jun 26, 2026 at 4:38 PM CEST, Maxime Ripard wrote:
> > > On Fri, Jun 26, 2026 at 04:16:39PM +0200, Luca Ceresoli wrote:
> > >> 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_connector_manager?
> > drm_bridge_connector_manager?
> > 
> > > 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.
> > 
> > What? o_O
> > 
> > Several encoder drivers have been painfully converted to create a
> > drm_bridge_connector.
> 
> I mean, it was done at a time where bridge hotplug wasn't a thing and
> the assumption was that the bridge chain is static. You're now breaking
> that assumption, it shouldn't come as a surprise that it might break
> other things.
> 
> And I know that you have experienced it already, which makes your
> reaction even more surprising to me :)
> 
> > Now if the bridges start doing it themselves we should go back to
> > those encoder drivers and ditch all the drm_bridge_connector from
> > there?
> > 
> > I must be missing something. Can you elaborate on this?
> 
> drm_bridge_connectors bring together a (complete) bridge chain and a
> connector. If you don't have either anymore, then we shouldn't keep it
> around.
> 
> What I was suggesting before was only a suggestion. I guess we could
> also make the encoder own the hotplug handling code and create the
> drm_bridge_connector when the chain is complete, and remove it when it's
> no longer the case.

That's an interesting option. We don't have to keep drm_bridge_connector
in its current form, but I don't think we should go back to individual
bridge driver creating connectors, especially now that we have bridge
chains where the connector ops are implemented collectively by multiple
bridges.

> We can discuss alternatives too. But either way, we shouldn't have it
> stick around.

-- 
Regards,

Laurent Pinchart