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Received: from AM7PR04MB7046.eurprd04.prod.outlook.com (2603:10a6:20b:113::22) by DU0PR04MB9587.eurprd04.prod.outlook.com (2603:10a6:10:317::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9769.15; Wed, 1 Apr 2026 06:43:56 +0000 Received: from AM7PR04MB7046.eurprd04.prod.outlook.com ([fe80::4609:64af:8a4b:fd64]) by AM7PR04MB7046.eurprd04.prod.outlook.com ([fe80::4609:64af:8a4b:fd64%3]) with mapi id 15.20.9769.016; Wed, 1 Apr 2026 06:43:56 +0000 Message-ID: <246ca728-1be6-4dd9-b228-7d99f28e1abe@nxp.com> Date: Wed, 1 Apr 2026 14:45:03 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7/8] drm/bridge: imx8mp-hdmi-tx: add an hdmi-connector when missing using a DT overlay at boot time To: Luca Ceresoli , Marek Vasut , Stefan Agner , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Frank Li , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Rob Herring , Saravana Kannan Cc: "Kory Maincent (TI.com)" , =?UTF-8?Q?Herv=C3=A9_Codina?= , Hui Pu , Ian Ray , Thomas Petazzoni , dri-devel@lists.freedesktop.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, Adam Ford , Alexander Stein , Anson Huang , Christopher Obbard , Daniel Scally , Emanuele Ghidoli , Fabio Estevam , Francesco Dolcini , Frieder Schrempf , Gilles Talis , =?UTF-8?B?R29yYW4gUmHEkWVub3ZpxIc=?= , Heiko Schocher , Joao Paulo Goncalves , Josua Mayer , Kieran Bingham , Marco Felsch , Martyn Welch , Oleksij Rempel , Peng Fan , Philippe Schenker , Richard Hu , Shengjiu Wang , Stefan Eichenberger , Vitor Soares References: <20260320-drm-lcdif-dbanc-v1-0-479a04133e70@bootlin.com> <20260320-drm-lcdif-dbanc-v1-7-479a04133e70@bootlin.com> <544112ab-8ca0-4622-b680-233457198e3e@nxp.com> <5f06ea5a-5388-440f-91d6-cebb0bee0a88@nxp.com> <9a6e74ed-d4ab-4f11-ab17-25e1a2b64b2d@nxp.com> From: Liu Ying Content-Language: en-US In-Reply-To: Content-Type: text/plain; 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>>>>>>> + label = "HDMI"; >>>>>>> + type = "a"; >>>>>> >>>>>> What if a board uses another type? >>>>> >>>>> For boards affected by this patch, currently the connector is created by >>>>> dw_hdmi_connector_create() which hardcodes type A [0], so there would be no >>>>> difference. >>>> >>>> Yes, that's from driver's PoV. However, userspace may get the type >>>> from /sys/firmware/devicetree/base/fixup-hdmi-connector/type and use it >>>> to do something. >>> >>> I'd say this is incorrect, the device tree is not an API for that. The >>> connector type might be known to the driver by other means (ACPI, DP MST, >>> whatever). So I think this is a non-problem. >> >> I just feel that it's not great to report potentially wrong type to users >> through the above sys node ... >> >>> >>> If userspace needs to know the connector type, that should come from the >>> ioctl (DRM_IOCTL_MODE_GETCONNECTOR perhaps). >>> >>>> Maybe, that's trivial. >>> >>> Not sure I got what you mean here, sorry. What are you referring to? >> >> ... with the above potentially wrong type being said, I think maybe this >> drawback is not a big deal and could be ignored. Sorry for not being >> clear in my last reply. > > Ah, clear now. No problem! > >>>>> Boards with a different connector should describe the connector in the >>>>> device tree, if they need to instantiate the exact type. >>> >>> I think this is the only valid solution. It's very easy to do, nothing new >>> to invent. >>> >>> Maybe on top of that we could add a warning when the overlay is applied, >>> e.g. "imx8mp-hdmi-tx used without a connector described in device tree; >>> adding a type A connector as a fallback; please add a valid description to >>> your device tree". >> >> I'd say this doesn't sound a bad idea but I hope the message is clear and >> short. > > What about: > > Connector description not found in device tree, please add one. Falling back to Type A. Maybe: Please add a hdmi-connector DT node for imx8mp-hdmi-tx. A fixup node in type a is added for now. > >>> Maybe pointing to a TODO entry in the documentation. >> >> To parameterize the HDMI connector type? If so, I'm okay with that. > > I was meaning a TODO entry to suggest people to add a connector description > to the dts. E.g., expanding on the above suggested warning: > > Connector description not found in device tree, please add one. See https://docs.kernel.org/gpu/todo.html#<...> > > And of course adding a TODO entry describing what one needs to do (add an > hdmi-connector node and link it to port@1 of the hdmi-tx). > > The drawback of the TODO is that items in todo.rst are supposed to be > removed eventually when done in the code, but this one cannot be removed > until some kernels printing the above logging message will be around, > i.e. potentially for decades. Not a big fan of adding a TODO entry, because those DT blobs without a hdmi-connector node could be out there forever, meaning the added TODO entry can never be removed. > > So maybe the simplest solution is just the first warning message + a > comment in the code right before the warning line, so it easily found with > grep or a web search by who sees the warning. +1. > > Luca > > -- > Luca Ceresoli, Bootlin > Embedded Linux and Kernel engineering > https://bootlin.com/ -- Regards, Liu Ying