Hi François, On Wed, 13 Oct 2021 at 11:35, François Ozog <francois.o...@linaro.org> wrote: > > Hi Simon > > Le mer. 13 oct. 2021 à 16:49, Simon Glass <s...@chromium.org> a écrit : >> >> Hi Tom, Bin,François, >> >> On Tue, 12 Oct 2021 at 19:34, Tom Rini <tr...@konsulko.com> wrote: >> > >> > On Wed, Oct 13, 2021 at 09:29:14AM +0800, Bin Meng wrote: >> > > Hi Simon, >> > > >> > > On Wed, Oct 13, 2021 at 9:01 AM Simon Glass <s...@chromium.org> wrote: >> > > > >> > > > With Ilias' efforts we have dropped OF_PRIOR_STAGE and OF_HOSTFILE so >> > > > there are only three ways to obtain a devicetree: >> > > > >> > > > - OF_SEPARATE - the normal way, where the devicetree is built and >> > > > appended to U-Boot >> > > > - OF_EMBED - for development purposes, the devicetree is embedded in >> > > > the ELF file (also used for EFI) >> > > > - OF_BOARD - the board figures it out on its own >> > > > >> > > > The last one is currently set up so that no devicetree is needed at all >> > > > in the U-Boot tree. Most boards do provide one, but some don't. Some >> > > > don't even provide instructions on how to boot on the board. >> > > > >> > > > The problems with this approach are documented at [1]. >> > > > >> > > > In practice, OF_BOARD is not really distinct from OF_SEPARATE. Any >> > > > board >> > > > can obtain its devicetree at runtime, even it is has a devicetree built >> > > > in U-Boot. This is because U-Boot may be a second-stage bootloader and >> > > > its >> > > > caller may have a better idea about the hardware available in the >> > > > machine. >> > > > This is the case with a few QEMU boards, for example. >> > > > >> > > > So it makes no sense to have OF_BOARD as a 'choice'. It should be an >> > > > option, available with either OF_SEPARATE or OF_EMBED. >> > > > >> > > > This series makes this change, adding various missing devicetree files >> > > > (and placeholders) to make the build work. >> > > >> > > Adding device trees that are never used sounds like a hack to me. >> > > >> > > For QEMU, device tree is dynamically generated on the fly based on >> > > command line parameters, and the device tree you put in this series >> > > has various hardcoded <phandle> values which normally do not show up >> > > in hand-written dts files. >> > > >> > > I am not sure I understand the whole point of this. >> > >> > I am also confused and do not like the idea of adding device trees for >> > platforms that are capable of and can / do have a device tree to give us >> > at run time. >> >> (I'll just reply to this one email, since the same points applies to >> all replies I think) >> >> I have been thinking about this and discussing it with people for a >> few months now. I've been signalling a change like this for over a >> month now, on U-Boot contributor calls and in discussions with Linaro >> people. I sent a patch (below) to try to explain things. I hope it is >> not a surprise! >> >> The issue here is that we need a devicetree in-tree in U-Boot, to >> avoid the mess that has been created by OF_PRIOR_STAGE, OF_BOARD, >> BINMAN_STANDALONE_FDT and to a lesser extent, OF_HOSTFILE. Between >> Ilias' series and this one we can get ourselves on a stronger footing. >> There is just OF_SEPARATE, with OF_EMBED for debugging/ELF use. >> For more context: >> >> http://patchwork.ozlabs.org/project/uboot/patch/20210919215111.3830278-3-...@chromium.org/ >> >> BTW I did suggest to QEMU ARM that they support a way of adding the >> u-boot.dtsi but there was not much interest there (in fact the >> maintainer would prefer there was no special support even for booting >> Linux directly!) > > i understand their point of view and agree with it. >> >> But in any case it doesn't really help U-Boot. I >> think the path forward might be to run QEMU twice, once to get its >> generated tree and once to give the 'merged' tree with the U-Boot >> properties in it, if people want to use U-Boot features. >> >> I do strongly believe that OF_BOARD must be a run-time option, not a >> build-time one. It creates all sorts of problems and obscurity which >> have taken months to unpick. See the above patch for the rationale. >> >> To add to that rationale, OF_BOARD needs to be an option available to >> any board. At some point in the future it may become a common way >> things are done, e.g. TF-A calling U-Boot and providing a devicetree >> to it. It doesn't make any sense to have people decide whether or not >> to set OF_BOARD at build time, thus affecting how the image is put >> together. We'll end up with different U-Boot build targets like >> capricorn, capricorn_of_board and the like. It should be obvious where >> that will lead. Instead, OF_BOARD needs to become a commonly used >> option, perhaps enabled by most/all boards, so that this sort of build >> explosion is not needed. > > If you mean that when boards are by construction providing a DTB to U-Boot > then I agree very much. But I don’t understand how the patch set supports it > as it puts dts files for those boards to be built. >> >> U-Boot needs to be flexible enough to >> function correctly in whatever runtime environment in which it finds >> itself. >> >> Also as binman is pressed into service more and more to build the >> complex firmware images that are becoming fashionable, it needs a >> definition (in the devicetree) that describes how to create the image. >> We can't support that unless we are building a devicetree, nor can the >> running program access the image layout without that information. >> >> François's point about 'don't use this with any kernel' is >> germane...but of course I am not suggesting doing that, since OF_BOARD >> is, still, enabled. We already use OF_BOARD for various boards that >> include an in-tree devicetree - Raspberry Pi 1, 2 and 3, for example >> (as I said in the cover letter "Most boards do provide one, but some >> don't."). So this series is just completing the picture by enforcing >> that *some sort* of devicetree is always present. > > That seems inconsistent with the OF_BOARD becomes the default.
I think the key point that will get you closer to where I am on this issue, is that OF_BOARD needs to be a run-time option. At present it has build-time effects and this is quite wrong. If you go through all the material I have written on this I think I have motivated that very clearly. Another big issue is that I believe we need ONE devicetree for U-Boot, not two that get merged by U-Boot. Again I have gone through that in a lot of detail. >> >> >> I can't quite pinpoint the patch where U-Boot started allowing the >> devicetree to be omitted, but if people are interested I could try a >> little harder. It was certainly not my intention (putting on my >> device-tree-maintainer hat) to go down that path and it slipped in >> somehow in all the confusion. I'm not sure anyone could tell you that >> rpi_3 has an in-tree devicetree but rpi_4 does not... >> >> Anyway this series is very modest. It just adds the requirement that >> all in-tree boards have some sort of sample devicetree and preferably >> some documentation as to where it might come from at runtime. > > That’s a very good goal. But adding files in dts make them not samples but > templates to be used and replace board provided DTB. > If you push all your DTS files in documentation, you do what you say: adding > sample files. >> >> That >> should not be a tough call IMO. Assuming we can get the validation in >> place (mentioned by Rob Herring recently) it will be quite natural to >> sync them between (presumably) Linux and U-Boot. >> >> I am also quite happy to discuss what should actually be in these >> devicetree files and whether some of them should be essentially empty. >> As you probably noticed, some of them are empty since I literally >> could not figure out where they come from! But there needs to be at >> least some skeleton for U-Boot to progress, since devicetree is >> critical to its feature set. > > absolutely. And thank you for your efforts to make that center stage. This is > also Linaro Edge group mist challenging task on the next 6 moths. Knowing > that we have lived in a floating situation for over 10 years, I just hope we > get consensus across projects and distro providers about the right end goal > and migration strategy. >> Thank you. >> >> >> It is high time we tidied all this up. I predict it will be much >> harder, and much more confusing, in 6 months. Just to set a road map here in case you can help unblock anything, here are the things I am aware of, excluding the things I have forgotten: - Ilias OF_PRIOR_STAGE, OF_HOSTFILE series - this series - the devicetree docs patch - devicetree bindings upstream for U-Boot (first patch under discussion) - bloblist as a means of passing devicetree, ACPI, tiny config info as C structs to U-Boot (needs to be written) - VPL so we can handle verification (patches pending) - bootflow / VBE v2 series (coming next week) Regards, Simon