Den 24.05.2020 20.35, skrev Daniel Vetter: > On Sun, May 24, 2020 at 7:46 PM Noralf Trønnes <noralf@xxxxxxxxxxx> wrote: >> >> >> >> Den 24.05.2020 18.13, skrev Paul Cercueil: >>> Hi list, >>> >>> I'd like to open a discussion about the current support of MIPI DSI and >>> DBI panels. >>> >>> Both are standards from the MIPI alliance, both are communication >>> protocols between a LCD controller and a LCD panel, they generally both >>> use the same commands (DCS), the main difference is that DSI is serial >>> and DBI is generally parallel. >>> >>> In the kernel right now, DSI is pretty well implemented. All the >>> infrastucture to register a DSI host, DSI device etc. is there. DSI >>> panels are implemented as regular drm_panel instances, and their drivers >>> go through the DSI API to communicate with the panel, which makes them >>> independent of the DSI host driver. >>> >>> DBI, on the other hand, does not have any of this. All (?) DBI panels >>> are implemented as tinydrm drivers, which make them impossible to use >>> with regular DRM drivers. Writing a standard drm_panel driver is >>> impossible, as there is no concept of host and device. All these tinydrm >>> drivers register their own DBI host as they all do DBI over SPI. >>> >>> I think this needs a good cleanup. Given that DSI and DBI are so >>> similar, it would probably make sense to fuse DBI support into the >>> current DSI code, as trying to update DBI would result in a lot of code >>> being duplicated. With the proper host/device registration mechanism >>> from DSI code, it would be possible to turn most of the tinydrm drivers >>> into regular drm_panel drivers. > > Do we have drivers with dbi support that actually want to reuse the > tinydrm drivers? Good clean is all good, but we need a solid reason > for changing stuff. Plus we need to make sure we're not just > rediscovering all the old reasons for why we ended up where we are > right now in the first place. > >>> The problem then is that these should still be available as tinydrm >>> drivers. If the DSI/DBI panels can somehow register a .update_fb() >>> callback, it would make it possible to have a panel-agnostic tinydrm >>> driver, which would then probably open a lot of doors, and help a lot to >>> clean the mess. >>> >>> I think I can help with that, I just need some guidance - I am fishing >>> in exotic seas here. >>> >>> Thoughts, comments, are very welcome. >> >> I did look at this a few months back: >> >> drm/mipi-dbi: Support panel drivers >> https://lists.freedesktop.org/archives/dri-devel/2019-August/228966.html >> >> The problem with DBI is that it has reused other busses which means we >> don't have DBI drivers, we have SPI drivers instead (6800/8080 is not >> avail. as busses in Linux yet). DSI and DPI on the other hand has >> dedicated hw controller drivers not shared with other subsystems. >> >> My initial tinydrm work used drm_panel, but I was not allowed to use it >> (at least not the way I had done it). > > Hm, do we have a summary of all the discussions/reasons from back > then? All I remember is that it's all that simple, you've done a lot > of work exploring all the options, I'm fairly sure I suggested > drm_panel even back then but somehow it didn't really work. Would be > good if we make sure we don't at least repeat history too much :-) > Unfortunately I don't have the two RFC series in my inbox anymore. I can see from this coverletter that drm_panel was removed after RFC v2: drm: Add support for tiny LCD displays https://patchwork.freedesktop.org/series/4520/ The problem is that there's no discussion in the relevant patch: https://patchwork.freedesktop.org/patch/80117/?series=4520&rev=2 What I remember is that someone said I couldn't use it, then I replied that someone suggested drm_panel to me in an earlier discussion, but I couldn't remember who. Then Emil chimed in and said he was the one that suggested it. Anyways let's see what Paul comes up with, if he finds a way to move SPI DBI over to drm_panel than I'm all for it. If not we'll just have to live with a hybrid solution I guess, one for MIPI DBI parallel bus for his hardware type and one for MIPI DBI SPI. The Pi also has a hw block for parallel DBI, downstream there's a driver that treats it as a generic parallel bus, since it's an 8080 compatible bus. If I'm not mistaken the BeagleBone Black also has a bus like this. When I started on tinydrm I had the idea to try and add a parallel bus type to Linux (even had a prototype for bit banging gpio) that I could use with DBI. This would make the bus available for things like FPGA's also, not just displays. I gave up on the idea since parallel DBI uses a lot of pins to upload a frame to display GRAM, much better to drive the panel directly through MIPI DPI (better fps), which all these SoC's also support. Noralf. > Cheers, Daniel > >> >> Noralf. >> >>> >>> Cheers, >>> -Paul >>> >>> >> _______________________________________________ >> dri-devel mailing list >> dri-devel@xxxxxxxxxxxxxxxxxxxxx >> https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
