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Mon, 29 Jun 2026 17:24:00 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1782746648; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=t9HMNcmuNOgHLZxwriuw4CBow1Oqe0l3xin2DE2AG/U=; b=KyKTA+gOIjf7GpxHnA2BZSNdQhPh/FN5WhHsijEVb+j6YeAbTaPwUR777uRBDlp/buzMQ7 SuG/NJVdaYV2mUiMF4Up/pg3J7xmsNrmKcsky6rPxNXvY08Kvqg9e3q+jcMyO1PKybzXdy 0or9lnIQOd2yh88sxr109v6Vp4KrCA1g2mh8Ea7iz/YGb0WK2/GuCI6qPyEjQCHP3SfQfw ny6brEttZe39S+lrHj7pO06RZi5KGB0oPj3Ju0dvnNMJmzIimpS8a/d2W3w2l/GtqGBpn3 Xab86sgnBfUIISwfU4LEMd86fdtFmDNKzEb88tL7mndHgSLTloSm4RhuhOyu3A== Precedence: bulk X-Mailing-List: imx@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 29 Jun 2026 17:23:59 +0200 Message-Id: Cc: "Maxime Ripard" , "Maarten Lankhorst" , "Thomas Zimmermann" , "David Airlie" , "Simona Vetter" , "Andrzej Hajda" , "Neil Armstrong" , "Robert Foss" , "Jonas Karlman" , "Jernej Skrabec" , "Inki Dae" , "Jagan Teki" , "Marek Szyprowski" , "Marek Vasut" , "Stefan Agner" , "Frank Li" , "Sascha Hauer" , "Pengutronix Kernel Team" , "Fabio Estevam" , "Hui Pu" , "Ian Ray" , "Thomas Petazzoni" , , , , To: "Laurent Pinchart" , "Luca Ceresoli" From: "Luca Ceresoli" Subject: Re: [PATCH 05/37] drm/display: bridge-connector: split code creating the connector to a subfunction X-Mailer: aerc 0.21.0 References: <20260519-drm-bridge-hotplug-v1-0-45e2bdb3dfb4@bootlin.com> <20260519-drm-bridge-hotplug-v1-5-45e2bdb3dfb4@bootlin.com> <20260608-mindful-heavy-frigatebird-be9faf@houat> <20260624-proud-unbiased-pony-ecc3c3@houat> <20260626-polite-hairy-perch-25e1aa@houat> <20260626-classy-nightingale-of-romance-1cacad@houat> <20260629144443.GA3106950@killaraus.ideasonboard.com> In-Reply-To: <20260629144443.GA3106950@killaraus.ideasonboard.com> X-Last-TLS-Session-Version: TLSv1.3 On Mon Jun 29, 2026 at 4:44 PM CEST, Laurent Pinchart 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: >> >> >> > 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_connecto= r into a >> >> >> >> >> dedicated function. This will be needed to be able to add (a= nd 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 t= ime based on >> >> >> >> hotplug events >> >> >> >> * the drm_bridge_connector is designated to create and rem= ove the >> >> >> >> drm_connector, so it must be persistent for the card lif= etime >> >> >> >> >> >> >> >> 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_connect= or 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 HDM= I >> >> >> > 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 everyt= hing >> >> >> > after the first hotplugged bridge to be destroyed, no? >> >> >> >> >> >> As said, it would be unregistered immediately but might be freed l= ater on >> >> >> if still refcounted. >> >> >> >> >> >> This is visible in patches 36+15, the path to follow is: >> >> >> >> >> >> drm_bridge_connector_handle_event(event =3D DRM_BRIDGE_DETACHED) = [patch 36] >> >> >> -> drm_bridge_connector_dynconn_release() [p= atch 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 reaso= n 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_bridg= e is >> >> either a bridge or something else". :) >> >> >> >> >> >> But let's leave names aside for a moment. If just looking at the curr= ent >> >> code, the drm_bridge_connector is "a handler, owned by the card/encod= er 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" appen= ded. >> >> >> >> 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. That's my understanding of the drm_bridge_connector too. > 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. Not sure I got what you mean. Currently drivers "opt-in" by: 1. passing DRM_BRIDGE_ATTACH_NO_CONNECTOR to drm_bridge_attach() 2. instantiating a drm_bridge_connector via drm_bridge_connector_init() Do you suggest changing that, so 1 and 2 are done transparently if the driver sets a new flag? >> > 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 las= t >> > 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. I proposed that, not because I "want" that but because for hotplug we need a way to know whether a DRM video pipeline is complete in the hardware or not. This is used in patch 36: /* Add the connector if the pipeline is now complete */ if (drm_bridge_connector_pipeline_is_complete(bridge_connector)) drm_bridge_connector_add_connector(bridge_connector); In other words, on a hotplug event (some new hardware was added), check whether the card is now complete _in the hardware_, and if it is create a drm_connector. In this series I proposed implementing it via a new .is_tail callback, that has been rejected during Dispaly Next Hackfest [0]. The idea that popped up there was that bridge drivers could expose the fwnode handler to the port@/endpoint pointing to the next bridge. I liked the idea but then I realized it would hardly fly in complex cases like bridges with dual-LVDS-or-two-single-LVDS output, e.g. SN65DSI84. So Maxime proposed [1]: ) Thanks for the notes, I think I largely agree with the discussion. ) Reading through it, I thought it would be nice for a new callback called ) get_next_bridge or something that would return either an error, NULL or = a ) (refcounted) pointer to the next bridge in the chain. And have some kind ) of special error (ENODEV?) when the bridge should be there but isn't ) (and thus the chain isn't complete). To me, "Making bridges aware if they are the last in the chain or not" is not a goal. It is just a technique to implement drm_bridge_connector_pipeline_is_complete(). I'm happy to implementing it in a different way if you have better ideas, but I haven't. [0] https://lore.kernel.org/lkml/DIXTUCXAU68V.1T7X89LMEUF2F@bootlin.com/ [1] https://lore.kernel.org/lkml/20260624-vagabond-neon-gorilla-cd6487@houa= t/ Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com