On Mon, 9 Mar 2020 21:59:26 +0200 Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > Hi Boris, > > On Mon, Mar 09, 2020 at 08:55:59PM +0100, Boris Brezillon wrote: > > On Mon, 9 Mar 2020 21:23:06 +0200 Laurent Pinchart wrote: > > > On Mon, Mar 09, 2020 at 11:50:59AM +0100, Philipp Zabel wrote: > > > > On Thu, 2019-11-14 at 14:17 +0100, Marek Vasut wrote: > > > > > The bus_flags and bus_format handling logic does not seem to cover > > > > > all potential usecases. Specifically, this seems to fail with an > > > > > "edt,etm0700g0edh6" display attached to an 24bit display interface, > > > > > with interface-pix-fmt = "rgb24" set in DT. > > > > > > > > interface-pix-fmt is a legacy property that was never intended to be > > > > used as an override for the panel bus format. The bus flags were > > > > supposed to be set from the display-timings node, back when there was no > > > > of-graph connected panel at all. > > > > > > > > That being said, there isn't really a proper alternative that allows to > > > > override the bus format requested by the panel driver in the device tree > > > > to account for weird wiring. We could reuse the bus-width endpoint > > > > property documented in [1], but that wouldn't completely specify how the > > > > RGB components are to be mapped onto the parallel bus. > > > > > > > > [1] Documentation/devicetree/bindings/media/video-interfaces.txt > > > > > > Things are funny sometimes, I've run into the exact same problem with a > > > different display controller today. > > > > > > Shouldn't we use the data-shift property from [1] to specify this ? > > > Combined with Boris' bus format negotiation for bridges, I think we > > > would have all the components in place to solve this problem properly. > > > > I wonder if we shouldn't take more complex pin mappings into account > > now and go directly for a data-mapping property describing those > > mappings using a string. This way we'd have a single property that > > would work for both fully parallel buses (DPI/RGB) and serial (or > > partially parallel) ones (LVDS). > > I'm all for standardization, but I'm not sure data-mapping is the right > property, at least with its current definition. It's really meant to > describe how individual bits are mapped to the LVDS time slots. I'm fine > extending it, but we need to define it clearly. How would you envision > it being used in this case ? > Well, clearly the data-width/data-shift approach does not solve all problems: what do you do if the source R pins are connected to the sink B pins? Well, the first answer would probably be 'have a serious discussion with the HW designer responsible for this insanity' :-), but once you've passed this 'WTF' stage, you'll have to find a way to tell the source component it should use RGBxyx while the sink should use BGRxyx (or vice-versa). This is something you can't extract that from those width/shift props though. My suggestion would be to have one string per MEDIA_BUS_FMT definition, so we can force things at the DT level if we really have to. That's basically what the interface-pix-fmt property was doing, except we would standardize the prop and values and probably provide helpers so bridge elements don't have to parse this prop manually. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
