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Received: from AM7PR04MB7046.eurprd04.prod.outlook.com (2603:10a6:20b:113::22) by GV1PR04MB10991.eurprd04.prod.outlook.com (2603:10a6:150:206::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8511.27; Tue, 11 Mar 2025 02:37:23 +0000 Received: from AM7PR04MB7046.eurprd04.prod.outlook.com ([fe80::d1ce:ea15:6648:6f90]) by AM7PR04MB7046.eurprd04.prod.outlook.com ([fe80::d1ce:ea15:6648:6f90%4]) with mapi id 15.20.8511.025; Tue, 11 Mar 2025 02:37:23 +0000 Message-ID: <77beb311-c836-4908-bfa6-fbeda69eee99@nxp.com> Date: Tue, 11 Mar 2025 10:38:37 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] dt-bindings: display: simple-bridge: Document DPI color encoder To: Maxime Ripard Cc: Rob Herring , Alexander Stein , dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, andrzej.hajda@intel.com, neil.armstrong@linaro.org, rfoss@kernel.org, Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se, jernej.skrabec@gmail.com, maarten.lankhorst@linux.intel.com, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch References: <20250304101530.969920-1-victor.liu@nxp.com> <20250304101530.969920-4-victor.liu@nxp.com> <20250304152320.GA2630063-robh@kernel.org> <1891036.atdPhlSkOF@steina-w> <20250305163805.GA2071011-robh@kernel.org> <7d98163d-10c8-457d-92e7-6a1d6e379beb@nxp.com> <20250306-kangaroo-of-pastoral-typhoon-8aefb2@houat> <0e82c4d6-8b93-4dd0-ae34-155e537ab344@nxp.com> <20250310-hopeful-helpful-quoll-e0dee8@houat> From: Liu Ying Content-Language: en-US In-Reply-To: <20250310-hopeful-helpful-quoll-e0dee8@houat> Content-Type: text/plain; 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März 2025, 16:23:20 CET schrieb Rob Herring: >>>>>>> On Tue, Mar 04, 2025 at 06:15:28PM +0800, Liu Ying wrote: >>>>>>>> A DPI color encoder, as a simple display bridge, converts input DPI color >>>>>>>> coding to output DPI color coding, like Adafruit Kippah DPI hat[1] which >>>>>>>> converts input 18-bit pixel data to 24-bit pixel data(with 2 low padding >>>>>>>> bits in every color component though). Document the DPI color encoder. >>>>>>> >>>>>>> Why do we need a node for this? Isn't this just wired how it is wired >>>>>>> and there's nothing for s/w to see or do? I suppose if you are trying to >>>>>>> resolve the mode with 24-bit on one end and 18-bit on the other end, you >>>>>>> need to allow that and not require an exact match. You still might need >>>>>>> to figure out which pins the 18-bit data comes out on, but you have that >>>>>>> problem with an 18-bit panel too. IOW, how is this any different if you >>>>>>> have an 18-bit panel versus 24-bit panel? >>>>>> >>>>>> Especially panel-simple.c has a fixed configuration for each display, such as: >>>>>>> .bus_format = MEDIA_BUS_FMT_RGB666_1X18 >>>>>> >>>>>> How would you allow or even know it should be addressed as >>>>>> MEDIA_BUS_FMT_RGB888_1X24 instead? I see different ways: >>>>>> 1. Create a new display setting/compatible >>>>>> 2. Add an overwrite property to the displays >>>>>> 3. Use a (transparent) bridge (this series) >>>>>> >>>>>> Number 1 is IMHO out of question. >>>>> >>>>> Agreed. >>>>> >>>>>> I personally don't like number 2 as this >>>>>> feels like adding quirks to displays, which they don't have. >>>>> >>>>> This is what I would do except apply it to the controller side. We know >>>>> the panel side already. This is a board variation, so a property makes >>>>> sense. I don't think you need any more than knowing what's on each end. >>>> >>>> With option 2, no matter putting a property in source side or sink side, >>>> impacted display drivers and DT bindings need to be changed, once a board >>>> manipulates the DPI color coding. This adds burdens and introduces new >>>> versions of those DT bindings. Is this what we want? >>> >>> There's an option 4: make it a property of the OF graph endpoints. In >>> essence, it's similar to properties that are already there like >>> lane-mapping, and it wouldn't affect the panel drivers, or create an >>> intermediate bridge. >> >> I don't see lane-mapping anywhere. Do you mean data-mapping instead? >> data-mapping is not defined in dtschema. Only lvds-codec.yaml defines >> data-mapping in endpoint. > > I meant as a general concept. The properties are data-lanes and > clock-lanes in > Documentation/devicetree/bindings/media/video-interfaces.yaml This requires referenceing video-interfaces.yaml in existing DT binding docs and driver modifictions, which adds burdens. > >> With option 4, I guess you meant display sink drivers, i.e., panel and >> bridge drivers, wouldn't be affected. Then, display source drivers, i.e., >> display controller and bridge drivers, would be affected. This adds >> burdens for driver developers/maintainers(though almost no effort from >> DT's PoV), doesn't it? > > Not necessarily, panels have a phandle to the parent endpoint too so > they can do that walk and configure their format if it's any easier. I'm sorry, I don't get your meaning here. I have no idea how to support this new property in endpoint-base(graph.yaml) or video-interfaces.yaml _without_ changing existing display source drivers. > >> Moreover, why it has to be the display sink drivers which are not affected? >> DT writers might choose to set the format at the sink endpoint, e.g., setting >> RGB666 at the sink endpoint of a RGB888 DPI panel or bridge. > > Why wouldn't you run the panel at the highest bpc possible? Because hardware designers route less data signals than regular ones to the DPI panel or bridge. > > Maxime -- Regards, Liu Ying