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

["Luca Ceresoli" <luca.ceresoli@bootlin.com>]

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:
>> 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_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. 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?

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com