Hi François, On Thu, 14 Oct 2021 at 12:13, François Ozog <francois.o...@linaro.org> wrote: > > > > Le mer. 13 oct. 2021 à 20:06, Simon Glass <s...@chromium.org> a écrit : >> >> 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. > > Doesn’t that mean that the current build system is not fully supporting > boards that do provide the DT and you try to hack your way in ? As I replied > to Tom, I could accept temporarily a void.dts containing nothing to actually > uallly pass any build problem until we properly fix the build system. > (But no “close to real” fake dts in the dts section)
Can you rephrase that paragraph, particularly the first setence? I am not sure what you are getting at. >> >> 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 know but a number of people do not agree with your position. U-Boot can > leverage many DTs coming from hats and capes to finalize the DT it passes to > OS. It can also leverage a file, a FIP section (NT_FW_CONFIG in TFA) a FIT > section formatted as FDT for its own configuration. Perhaps it wasn't clear from the context, but I was talking about the devicetree for U-Boot, i.e. the control DTB for U-Boot. It's fine to merge overlays, etc. to pass to Linux, of course. >> >> >> >> >> >> >> >> 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 > > the “ABI” of U-Boot entry need more specification. Having something close to > Linux helped to get U-Boot in the RPI4 and other boards I believe. So we > could start from here. The blob list may be an extra arg (x0=DTB, x1=bloblist > in Arm). Yes that's my intent, hopefully in a few weeks. >> >> >> 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
