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bh=51Grhzs4J/AFDPyUowVuD4CPAJKfF+m68stnN1IxSsQ=; b=umlSJpL4AIbsgAirTydRVbGpf5107Ii+GVjOI8QitEF2dkyJuaiECJesJxtJG20O7h1k47 AZzwstqTauowTH+yizoGHwCmb3eBPK+0U7ld637Jw+ewzd9sdJllgbj6qcSqnCqbS2s4Lz e6eW6TvGnxPbW+kxe8J8Ic72akzbbqhgxWdgMSydSDeWWharfscuamENZrXsXX89bL02Xy I6bWtB2YJ158MZfbdVGtg5bpVY09ySZeqEJoeVj30xpJ8+xR2qhD8qd0xENz0DUVo/pSf3 o4bIEOLmEFGmqTin47ONTWv74aSUZ4IrDqIU5H83+MwBQaNyDu19idYFAYk7pw== Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Thu, 16 Jul 2026 10:37:24 +0200 Message-Id: Subject: Re: [PATCH 05/37] drm/display: bridge-connector: split code creating the connector to a subfunction Cc: "Luca Ceresoli" , "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" , "Maxime Ripard" From: "Luca Ceresoli" X-Mailer: aerc 0.21.0 References: <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> <20260707-warping-goshawk-of-swiftness-beea4a@penduick> <20260707123205.GB211515@killaraus.ideasonboard.com> In-Reply-To: <20260707123205.GB211515@killaraus.ideasonboard.com> X-Last-TLS-Session-Version: TLSv1.3 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260716_013742_546944_32C0C79E X-CRM114-Status: GOOD ( 47.51 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Maxime, Laurent, On Tue Jul 7, 2026 at 2:32 PM CEST, Laurent Pinchart wrote: > 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 wro= te: >> > >> >> >> >> In preparation to introduce bridge hotplug, split out from >> > >> >> >> >> drm_bridge_connector_init() the code adding the drm_connec= tor 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 cal= ls 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 r= emove the >> > >> >> >> drm_connector, so it must be persistent for the card l= ifetime >> > >> >> >> >> > >> >> >> As the lifetimes of drm_bridge_connector and drm_connecto= r 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_conne= ctor into a >> > >> >> >> dedicated function. No functional changes, just moving co= de around for >> > >> >> >> now. A future commit will make the drm_connector be creat= ed 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 H= DMI >> > >> >> > connector, and then swapping out the hotplugged part for an LV= DS one? >> > >> >> > Does the HDMI connector sticks around indefinitely? >> > >> >> >> > >> >> In your example, the HDMI drm_connector would be unregistered an= d put on >> > >> >> hotunplug. Its allocation will stick around until the last put b= ut 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 ever= ything >> > >> >> > 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 =3D 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 rea= son 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 clea= r 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_bri= dge is >> > >> either a bridge or something else". :) >> > >> >> > >> >> > >> But let's leave names aside for a moment. If just looking at the cu= rrent >> > >> code, the drm_bridge_connector is "a handler, owned by the card/enc= oder 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" app= ended. >> > >> >> > >> So in both cases there needs to be "a handler persitent with the ca= rd". >> > >> >> > >> 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 l= ast >> > > 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 bri= dge >> > > 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. Sure adding a new requirement (hotplug) breaks the existing design. Still, this can be solved either by adding a new software component or by extending the existing software component (drm_bridge_connector) as this series proposes. None of the two ideas is wrong, so let's discuss which is best. >> And I know that you have experienced it already, which makes your >> reaction even more surprising to me :) Sure, the drm_bridge allocation was not refcounted and needed to be. And we didn't ditch the drm_bridge to create a new thing, we instead extended the existing software component (drm_bridge) to also be refcounted. >> > 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. I definitely agree we don't want to add burden back on the encoder. >> We can discuss alternatives too. But either way, we shouldn't have it >> stick around. Bottom line, I roughly see three ideas mentioned: 1. (this series) extend the drm_bridge_connector to create the drm_connector based on bridge hotplug events [+rename it] 2. - keep the drm_bridge_connector (mostly) as is - let each encoder driver add/remove it based on bridge hotplug events =3D> more burden on encoder drivers -> no 3. - keep the drm_bridge_connector (mostly) as is - add a new component (what name?) that will receive bridge hotplug events and react to them by adding/creating a drm_bridge_connector - modify encoder drivers to create this new object instead of the drm_bridge_connector In principle option 3 is the same as option 1, except it is split in two components. I _think_ you both are discussing option 3. Correct? If that's correct: any name suggested for the new component? drm_hotplug_manager? drm_connector_manager? drm_bridge_connector_manager? Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com