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Received: from AM7PR04MB7046.eurprd04.prod.outlook.com (2603:10a6:20b:113::22) by GV1PR04MB10306.eurprd04.prod.outlook.com (2603:10a6:150:1c9::22) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9745.28; Tue, 31 Mar 2026 03:02:10 +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 15.20.9745.027; Tue, 31 Mar 2026 03:02:10 +0000 Message-ID: <9a6e74ed-d4ab-4f11-ab17-25e1a2b64b2d@nxp.com> Date: Tue, 31 Mar 2026 11:03:14 +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> 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. > >>> OTOH how can a common module know the specific connector? >> >> Hmm, maybe add a module parameter or let users set the type through Kconfig > > I'm afraid none of this would work for distribution kernels, where who > configures the distribution has no idea on how many different hardware it > will run. > >> or even define an unknown type to honestly tell users that we don't know it? > > This sounds like a potentially valid idea, even though I'm not fully > convinced. Also I suspect it would be a pretty large change, and also > adding "unknown type" in the device tree seems not compliant with the rule > that DT describes the hardware (not the lack of info about the hardware). > > But definitely it's not needed for this specific case, because: > > * with current code, every imx8mp-hdmi-tx usage adds a type-A connector [0] > * with this patch the correct type will be created when described in DT, > and type-A will be used only as a fallback when the DT is lacking > > So after the patch we'd do sometimes better, never worse in this respect. Well, kind of a bit worse since the sys node exposes a potentially wrong type. > > Based on the above I'm sending v2 soon, but don't hesitate in following up > in case I may be missing something (this topic is tricky). Agreed, it's tricky. > > [0] https://elixir.bootlin.com/linux/v7.0-rc5/source/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c#L2601 > >>> 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. > Maybe pointing to a TODO entry in the documentation. To parameterize the HDMI connector type? If so, I'm okay with that. > > What do you think about this? > > Thanks again for your careful review! Thanks for your patches! Appreciated. > > Luca > > -- > Luca Ceresoli, Bootlin > Embedded Linux and Kernel engineering > https://bootlin.com/ -- Regards, Liu Ying