On Fri, Mar 07, 2025 at 11:10:00AM +0800, Liu Ying wrote: > On 03/06/2025, Maxime Ripard wrote: > > On Thu, Mar 06, 2025 at 03:02:41PM +0800, Liu Ying wrote: > >> On 03/06/2025, Rob Herring wrote: > >>> On Wed, Mar 05, 2025 at 10:35:26AM +0100, Alexander Stein wrote: > >>>> Hi, > >>>> > >>>> Am Dienstag, 4. 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 > 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. > 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? Maxime
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