On Wed, Jan 6, 2021 at 10:35 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > On Wed, Jan 6, 2021 at 12:21 AM Rob Herring <robh+dt@xxxxxxxxxx> wrote: > > > > On Tue, Jan 5, 2021 at 4:24 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote: > > > > > > Hello, > > > > > > Here is an attempt to make some changes in the kernel to allow building > > > of device tree overlays. > > > > > > While at it, I would also like to discuss about how we should mention > > > the base DT blobs in the Makefiles for the overlays, so they can be > > > build tested to make sure the overlays apply properly. > > > > > > A simple way is to mention that with -base extension, like this: > > > > > > $(overlay-file)-base := platform-base.dtb > > > > > > Any other preference ? > > > > Viresh's patch is not enough. > > We will need to change .gitignore > and scripts/Makefile.dtbinst as well. > > > In my understanding, the build rule is completely the same > between .dtb and .dtbo > As Rob mentioned, I am not sure if we really need/want > a separate extension. > > > A counter approach is to use an extension like '.ovl.dtb' > It clarifies it is an overlay fragment without changing > anything in our build system or the upstream DTC project. > > We use chained extension in some places, for example, > .dt.yaml for schema yaml files. > > > > dtb-$(CONFIG_ARCH_FOO) += \ > foo-board.dtb \ > foo-overlay1.ovl.dtb \ > foo-overlay2.ovl.dtb > > > Overlay DT source file names must end with '.ovl.dts' I like that suggestion as then it's also clear looking at the source files which ones are overlays. Or we'd need .dtso to be consistent. > > I think we'll want something similar to how '-objs' works for modules: > > > > foo-board-1-dtbs := foo-board.dtb foo-overlay1.dtbo > > foo-board-2-dtbs := foo-board.dtb foo-overlay2.dtbo > > foo-board-1-2-dtbs := foo-board.dtb foo-overlay1.dtbo foo-overlay2.dtbo > > dtbs-y += foo-board-1.dtb foo-board-2.dtb foo-board-1-2.dtb > > > > (One difference here is we will want all the intermediate targets > > unlike .o files.) > > > > You wouldn't necessarily have all the above combinations, but you have > > to allow for them. I'm not sure how we'd handle applying any common > > overlays where the base and overlay are in different directories. > > > I guess the motivation for supporting -dtbs is to > add per-board -@ option only when it contains *.dtbo pattern. I hadn't thought that far, but yeah, that would be good. Really, I just want it to be controlled per SoC family at least. > But, as you notice, if the overlay files are located > under drivers/, it is difficult to add -@ per board. Generally, they shouldn't be. The exceptions are what we already have there which are old dt fixups and unittests. We want the stripped DT repo (devicetree-rebasing) to have all this and drivers/ is stripped out. (Which reminds me, the DT repo will need some work to support all this. It's a different build sys.) > Another scenario is, some people may want to compile > downstream overlay files (i.e. similar concept as external modules), > then we have no idea which base board should be given with the -@ flag. > > > I'd rather be tempted to add it globally > > > ifdef CONFIG_OF_OVERLAY > DTC_FLAGS += -@ > endif We've already rejected doing that. Turning on '-@' can grow the dtb size by a significant amount which could be problematic for some boards. > > Another thing here is adding all the above is not really going to > > scale on arm32 where we have a single dts directory. We need to move > > things to per vendor/soc family directories. I have the script to do > > this. We just need to agree on the vendor names and get Arnd/Olof to > > run it. I also want that so we can enable schema checks by default > > once a vendor is warning free (the whole tree is going to take > > forever). > > > If this is a big churn, perhaps we could make it extreme > to decouple DT and Linux-arch. I would be fine with that, but I don't think we'll get agreement there. With that amount of change, we'll be discussing git submodule again. Rereading the thread on vendor directories[1], we may just move boards one vendor at a time. We could just make that a prerequisite for vendor supporting overlays. > arch/*/boot/dts/*.dts > -> dts/<vendor>/*.dts > > Documentation/devicetree/bindings > -> dts/Bindings/ > > include/dt-bindings/ > -> dts/include/dt-bindings/ > > > > Then, other project can take dts/ > to reuse for them. This is already possible with devicetree-rebasing.git. Though it is still by arch. Rob [1] https://lore.kernel.org/linux-devicetree/20181204183649.GA5716@bogus/
