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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

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:
> >> >> > 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?

I'm fine with a rename. When developing drm_bridge_connector I've always
envisioned it as code that manages the creation of a connector for a
chain of bridges. In particular, the drm_bridge_connector object is
*not* and has never been a bridge.

Ideally all this should move to the DRM core and be transparent to
drivers. Drivers could set a flag somewhere to opt-in for connectors
managed by the DRM core.

> > 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.

I don't think bridges should be aware of whether or not they're the last
one in the chain.

> > 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. 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?

-- 
Regards,

Laurent Pinchart